I was recently asked to create a Density Altitude version of BallisticXLR for those that like DA over absolute air density. Ok, fine. Done. It took quite a number of hours to port it over but it’s there now and it works. This new system is meant for shooters that need extremely rapid ballistics data that is easy to read under time pressure and that can deal with atmospheric changes extremely rapidly.
And here it is!
The inputs page is a very close match to the original BallisticXLR inputs page but unlike BallisticXLR does not require any atmospheric data inputs. BallisticPRS also differs from BallisticXLR in that it does not have the Primary or Secondary Functions tabs and a number of other tabs that are not relevant for DA applications. It does come with the reloading cost calculator, projectile database, reticle subtend tab, and sniper range cards.
BallisticPRS is meant for the experienced shooter while still being easy enough to use that beginners will not find it stammeringly confusing. As seen below the data tables are noted in meters or yards with data in 10yrd/m increments from 100 to 2490. Data for Drop, Wind, Movers, H-Cor, V-Cor and Spin are listed in a single row making for very fast info uptake.
There’s an included DA tab (which is experimental) that will allow the user to identify a correct DA with a non-standard temperature and a pressure altitude reading. This handy feature will assist the shooter as temperatures change throughout the day in their FFP.
This latest product is free for download and; just like with BallisticXLR, I provide free email based support. Just like BallisticXLR, BallisticPRS requires genuine Microsoft Excel for correct function. I’ll be adding a new BADEDS and B-FEDS kit with the DA tables shortly. Because of the much larger page count these kits will be modestly more expensive.
I’m very excited about this new product and I think you will be too!
P.S. – Being that it’s Memorial Day as I post this, I thought I’d leave this here. The price of freedom for some is said to be the blood of patriots and tyrants. It could also be termed the blood of our children and our parents. Dead and living soldiers bought this day off for us.
A reticle is simply a set of markings inside an optical device for use in measuring, pointing, aiming, etc… My 8″ Newtonian telescope comes with an eyepiece that you can use for aligning the telescope with the Earth properly so its drive motor programming can drive it to pre-determined stars and planets automatically. Inside that eyepiece is a reticle of sorts, there are several stars and constellations. You adjust the scope to place the legs facing north and those reticle elements on the actual image of the sky. Once the reticle and the real stars are aligned, the telescope is aligned. Nifty huh?
In weapon scopes we have quite a lot of variety. Part of that comes from the variety of weapon types and part comes from the variety of ways those weapons may be utilized. There is such a thing as a general purpose rifle scope which would tend to come with a general purpose reticle. Anything that’s meant to be general purpose can be pressed into service for most needs but it’s not going to be optimal for probably any of them. This means it’s important to select your reticle with the same pickiness that you’d select your rifle, your ammo or your boots. Make sure it’s up to the task.
Reticle designs have exploded in number and manufacture method in recent years. As people have crafted solutions to new and old problems, the number of reticles and their specialization has dramatically increased. What many will find surprising is how astonishingly old most of the technology used today is. There is some exciting technology that’s been developed in more recent years but the fundamental method for creating a reticle hasn’t changed in centuries.
Reticle Manufacture Methods:
In the oldest days you may have had a simple crosshair which would have literally been a pair of intersecting spiderwebs (which are astonishingly strong and flexible) or actual hairs (later wires) tied between posts inside the scope. Primitive and fragile though they are, they solve the first problem: The aim point. Now there is one instead of just a view of some section of the target with no identified center. Before long it was realized that there was a growing need for more sophisticated aiming points and for those points to be useful for intelligence gathering. Thankfully the technology to make such a thing had existed for a very long time already. One problem a wire crosshair will never experience is flecks of debris appearing to float on or around the reticle. That only happens with etched reticles because of gravity, which brings us to:
As early as the 1700’s crafty people were thinking of etching a reticle onto glass. This practice allows extreme flexibility in reticle design as floating elements can be very easily accommodated. This is the dominant system in top quality magnified rifle scopes today. Some have said that etched reticles are less durable than wire (Wikipedia). I would dispute the hell out of that. A genuine problem brought in by etching is that the etched bit will disperse some light thereby lessening transmission marginally more than a wire reticle. Etched reticles are more expensive and difficult to manufacture and they are going to be able to rotate which is annoying and unhelpful and requires advanced adhesive technology or mechanical impingement systems. Where wire hairs may break under the stress of a big shock (like dropping the rifle), etched reticles may also rotate after a big shock. Etched reticles also exist on their own hunk of glass. Glass isn’t going to transmit 100% of the light so you will lose some.
Reflected reticles aren’t inline with the incoming light like wire and etched reticles. Reflected (called Reflex) reticles are literally projected onto a lens at an angle and the image reflected back to the shooter superimposed and collimated with the target image. The AimPoint CompM2 uses this system as do many red dot sights. The need to project light onto the lens through which the primary image is coming means that there’s a sort of minimum line width and brightness which is pretty beefy when compared to a wire or etched reticle. There’s also the potential problem of bloom. Bloom is not entirely common anymore but it consists of a scatter effect like looking into bright lights at night. Reflex reticles which are high quality will not exhibit bloom. Because there are no physical parts of the reticle you can get very creative about reticle design just like with etched reticles. Battery life with these can be ridiculously long (on the order of years of power-on running) because of the low power output needs of the illuminator. The Burris FastFire III uses this system.
Holographic reticles are much like Reflex reticles in that they use light to bring the reticle to life. Unlike Reflex sights that project light onto an interior surface to form the reticle, a holographic sight uses an etching on a lens element in the primary optical path which is illuminated by collimated laser diode. It’s a bit like a mixture of an etched reticle with an illuminated/reflex reticle. Similar to Reflex sights, holographic sights can suffer from bloom. Battery life with these can be poor compared to a Reflex sight due to increased power needs to illuminate the hologram. Eotech 512.A65’s use this system.
Reticle Focal Plane:
Focal plane is pretty simple to contemplate. First focal plane refers to the placement of the reticle element literally near the front of the scopes internals with the result of the reticle being the same angular size relative to the target or object being viewed. If I were to wear a t-shirt with a big X on it and walk towards you, you’d see the X get bigger and bigger because it’s attached to me. Second focal plane refers to the reticle always staying the same size. This can be modeled by placing a big wire X a few feet in front of you and having the target move toward you but not having the X move. The X would appear to stay the same size while the targets apparent size would continuously change. Each has its place. This only matters with variable magnification scopes. With a fixed power scope, since magnification never changes, the actual location of the reticle becomes largely immaterial.
First Focal Plane:
First focal plane reticles are necessary if you want to use a reticle for estimating range to target and to be able to do so at any of the available magnification levels of your optic without having to take additional steps in the math or actions such as setting the magnification to a specific level. FFP reticles are wildly popular in the tactical/tacticool/sniper/long-range worlds where you’re shooting for hits rather than for X’s. FFP scopes will be more expensive than second focal plane if that’s the only difference between them. The reason is simple, another lens near the front of the scope. It’s a small and necessarily finely crafted lens with an exactingly precise reticle etched into it and it’s placed very far toward the front of the system of lenses by necessity. Small things that are super finely crafted and placed deep inside complicated mechanisms are expensive. That’s how things work. The lines inside the reticle on a FFP scope are at precise angular distances from each other and can be placed over other elements in the image to compare angular size. If you know the angular size and the actual size of the thing you’re looking at you can deduce how far away it is. When you increase magnification on an FFP scope the crosshair will appear to grow in direct proportion to the apparent size of the target. At low magnifications a FFP reticle may be little more useful than a standard Duplex. At high magnifications it may occlude quite a lot of the image of the target. That’s not going to be super helpful to people shooting for X’s but it is a very fast way to range and hold-off and allows the shooter to rapidly engage targets with lower magnification and to precisely compensate for wind, movement, etc… without having to fuddle with turrets.
Second Focal Plane:
Second focal plane reticles are desirable any time you want a fine reticle to stay fine as magnification changes. It might seem odd to some reading this, but sometimes folks do want that feature. Because the lens is placed closer to the rear of the scope and not deep inside its guts there’s typically a little more room for using a larger lens element, or even for just stringing a pair of wires across each other (some still do that). Because it’s SFP the lens element with the reticle can more durably be installed and it’s easier to fabricate, easier to install and cheaper because of that. Just because a scope is SFP doesn’t mean it’s not as good as a FFP scope. They have their purposes, each of them. Second focal plane scopes are extremely popular in target shooting applications where group size is measured and for hunting. If you’re shooting for X’s you’re going to be best served by a SFP scope.
Fine, Duplex, Post, Mil-Dot, Circle, Target Dot, Christmas Tree, Hunter Ranging, SVD… Which one is right for you. You want the least complicated reticle that can do the job you need it to do. Having too much going on in the scope will absolutely slow the shooter down which will require more training to overcome. Below we’ll introduce some common reticles and some not so common ones and give a brief blurb about common uses for each. This is by no means going to be comprehensive because much like a screwdriver handle occasionally will become a hammer, a target scope sometimes will get used for hunting. Neither works great for off-book use cases but they can be made to work.
A fine crosshair is the simplest reticle that’s in common use. Two wires are crossed to form the X or T or whatever letter you wanna call it. They’re typically pretty fine and their width is controlled by using wider or narrower wire to make them. In low light situations these can be very difficult to use and if they’re the old school type that are actually made of hair or spiderweb or wire then breakage is a concern. Benchrest shooters, people shooting for X’s and those shooting for group size will quite often choose this layout along with extremely high magnification as it obscures the least possible amount of the target so they can see their bullet holes, even from a great distance and even with very small bullets.
Duplex reticles are a fine-ish crosshair in the center that grows to be quite wide nearer the edges. The transition is normally abrupt rather with a very short triangular taper. These are just about perfect for hunting non-dangerous big game with a rifle. Low light situations are helped by the wider lines and precision isn’t hampered because the crossing lines are still fine. The thicker lines guide your eye naturally to the center so they’ll much more easily pick up the fine hairs in low light. This is probably the most popular reticle in the USA and is used on the vast majority of hunting rifles that are equipped with a scope. Some companies have made FFP versions (the 30/30 reticle for example) but most are on SFP scopes.
Also called the German reticle provides an open field of view with minimal stuff going on and is ideal for hunting dangerous game and was heavily used in early eastern European sniping scopes. The thick center vertical post is quick to pick up even in low light. The pointed top of the post allows combat sniping precision without a temptation for the sniper to spend too much time refining their aim point. The thick horizontal bars at the edges help the sniper avoid canting the rifle. The reticle is simple to make and lacks ranging stadia. For German snipers in WWII this was very effective. When hunting dangerous game or hunting in a dangerous environment the lack of extraneous stadia makes for a very high level of situational awareness and increased speed of use. Things don’t always need to look fancy to be sophisticated. This forms the foundation of the much more sophisticated SVD type discussed further below.
Scopes with reticles with miliradian subtends can be used very easily for range estimation and provide a brilliant method of fire correction. There are 2*Pi radians in a circle which isn’t helpful for most people. In the interests of not making you do math, suffice it to say that for 1 radian there are about 57degrees of arc. That’s a huge amount of arc so we cut it into 1000 little pieces which are very approximately .3 minutes of angle each (which works out to about .36 inches at 100yards). There are 60 minutes in each degree so we’re talking about a very fine set of intervals which allows very small differences in target size to be helpful in estimating target range which makes for great precision. Why not use minutes of angle? When using Mils/MRAD everything we do is in base10 and we tend to do it with metric measurements of the target and world which makes for easy math. Minutes of angle on the other hand uses base60 (thanks ancient fertile crescent residents for the hellish system of mathematics) and the SAE measurement system (feet/inches) is base12. Base60 and base12 are compatible in places (12*5=60 right) but they’re not easy to mix in your head and few of us have 12 fingers to count on to help. Scopes with their reticles in mil-scale and with mil-scale turrets make fire corrections ridiculously simple, especially if you use metric linear measurements for target size and range. With a scaled reticle like these and turrets in MRAD you can watch where your bullet landed, measure it in the reticle, adjust exactly that much up/down/left/right and fire. There’s no converting to or from minutes of angle and no guesswork. Scopes with mil-scale reticles are wildly popular in many forms of shooting including PRS, Long Range Tactical, 3-Gun, etc.. as well as with tactical/SWAT units of police departments and military snipers. If you need flexibility between being able to deliver slow precision fire and being able to deliver rapid and effective if slightly less precise fire (precision and speed are mutual enemies).
This is more or less the same as a mil-scale but instead of using miliradians they will use minutes of angle or some fraction thereof. All the same basics in use case apply from mil-scale to moa-scale. There are reasons to use a MOA-scale reticle and it’s entirely probable that if you need one, you know it and know why. There is also a sub-type of MOA scale which is IPHY or inch per hundred hards. 1MOA is 1.05 (or 1.09 depending on how you measure) inches at 100 yards. Because different scope companies had different ideas of how to measure 1MOA some other companies decided to say the heck with it and adopted a system which is exactly 1 inch at 100yards. The math is much easier to do in your head without extraneous decimal places in the significant digits. While IPHY is by definition not MOA it’s very very similar. Both have smaller linear distances covered at any distance than MRAD with IPHY having the smallest subtended linear distance. The small value lends itself to a smaller click value and the ability to dial more precise adjustments. For target shooters an IPHY scale would probably make sense. For those that just can’t grok the metric system of linear measures, the MOA scale is probably up your alley (though you should really learn the metric system for your own benefit).
These used to be nearly exclusive residents of the realm of shotgun scopes but someone figured out that they make brilliant combat reticles because they’re super fast and easy to use. Put your target in the circle and kill it. Simple. Now we’re starting to see really clever things like circle reticles being placed in the second focal plane and a secondary crosshair or scaled reticle being placed in the first focal plane in the same scope. This in theory enables the shooter to engage long range precision targets as well as deal with high intensity combat at conversational to hollerin’ distances. That combination is finding more and more appreciation within the 3-gun world as well but still has its home in more genuinely deadly use cases. This is a case of everything and the kitchen sink. It’s not going to be perfect for most anything except for giving someone in battle a leg up if they’re well trained with it.
This may consist of a simple dot in the center of the field of view but is more commonly combined with a fine crosshair. The dot may cover anything from 1/8moa to 3moa or more. These are popular with many sorts of target and varmint shooters. The tiny dot moving over your target gives an easy to see and fast to pick up signal to the brain to pull the trigger while the fine crosshairs give an aid in not canting the rifle. In metallic silhouette competition these are wildly popular especially in very high magnification scopes. Varmint hunters seem to really like the hair:dot system as well as many target disciplines which go by X count or group size or both.
These are a more recent development which has gained popularity across the shooting sports and military world. These consist normally of a first focal plane mil-scale cross-hair reticle which is then decorated with elevation and windage stadia in something of a pyramid below the primary horizontal cross-hair. While pretty busy in the eye these reticles allow for the user to hold off from the center of the target to account for range, wind and movement without having to twist the turrets. That makes these a potentially incredibly fast scope to use particularly on ultra challenging PRS courses because you can transition from close targets to far targets without having to tinker with your scope. Horus has come up with a pretty big selection of this type of reticle. There are also many proprietary reticles of this type. When selecting this type of scope reticle for use it’s important to know about how much training you’ll need to do to be proficient with it as well as picking the exact design that well suits your needs. These make a pretty poor scope for shooting for groups or X’s in competition, they’re not ideal for most hunting situations either. They’re fantastic for speedy target acquisition and engagement in tactical and simulated tactical pursuits.
Ballistic Drop Compensating / Hunter Ranging:
Ballistic Drop Compensating (BDC) reticles come with additional intersecting lines on the vertical post that correspond to various ranges based on your muzzle velocity and bullet choice. These are fine for short to intermediate ranges but rapidly lose veracity as range increases. Up to about 400 yards they’re great but after that actual ballistics should be referred to to assure a humane harvest of your target animal. Some of these reticles like the Bushnell 30/30 (which appears to be a regular duplex until you find out it’s first focal plane) are meant specifically for deer hunters so they can quickly range their target. There’s a long running debate in some circles about whether including ranging and distance compensation features in a hunting scope is really worthwhile or if it’d be better to either not have them or to get a scope with those features fully implemented, like a mil-scale scope. While mil-scale reticles and MOA scale reticles have their secondary line intersections at precisely equal angular distances, BDC type reticles almost uniformly do not place the secondary aim points at even intervals. This makes them more difficult to train on, memorize and apply to new situations and environments. BDC reticles are generally limited to .5km distances and should be as things like air temperature and barometric pressure really start to matter around there. For people with a small area of operations and a mission profile that allows for shots being limited to 500m or under these are pretty good options for shooting at meat. For target use, they’re generally inappropriate but like a screwdriver handle can become a hammer, a BDC scope can be pressed into service as a target scope with some performance consequences.
A fairly unique reticle that’s more or less limited to eastern bloc Soviet aligned countries’ sniper rifles. This reticle is actually a series of them. There’s a ranging box meant for use with human and human sized targets to provide rapid range estimation. There are chevrons which provide hold-overs and there is a horizontal mil-scale for hold-offs and whatever else you find you need them for. While being possibly the foundation of the ideal universal reticle the SVD reticle just hasn’t caught on with western shooters like those above have. It’s not meant for precision but instead; and in a very Soviet way, for combat. It’s meant to allow poorly trained designated marksman to put reasonably accurate fire against human and materiel targets with the least amount of hassle (training) possible. Where western armies developed doctrine that used snipers as force multipliers and intelligence gathering resources, the Soviets were less interested in having front line troops reporting intel back up and seemed happy to have them just go ahead and engage the enemy. Again, pretty standard Soviet thinking. They did understand ever since WWII that effective use of large numbers of designated marksman does sap the heck out of your enemies will to fight and their ability to freely move around and this sort of reticle is ideal for that. It’s not very good at all as a target reticle for any pursuit where you’re counting group size or X’s but like everything, can be pressed into service with consequences.
Choosing the Right Reticle for You:
First: remember that a fine crosshair is about the standard minimum. Every reticle feature or element after that that you add in after that will either increase the cost of your final product, orient your scope for use in one pursuit or another or force the manufacturer to reduce its quality to maintain profitability. So, keep it as simple as you can and don’t buy what you won’t use. We all want the whizz-bang-est scope in the world. It’s nice to own the best when the best is measured by its cost. In this case though the best is that which accomplishes the mission without costing you anything extra.
While you’re shopping around decide if you need first or second focal plane first. This will be the thing that limits your available selection the most. If you shoot competitions at unknown ranges then first focal plane is almost dictated if you want to not have to lug around a laser rangefinder. If you shoot in competitions where group size is important then you’ll probably be best served by second focal plane. That’s a good rule of thumb but not gospel so think about it and see what others are using before you make a purchase. Other competitors are going to on average have a set of features in common and are your best source of comparative shopping especially since they’ll usually be pretty generous about letting your look through and compare different brands and models. Hunting at close to intermediate (<500yrds) ranges won’t make any dictates about FFP vs. SFP but anything further you’ll want to consider the environment (vegetation, terrain, species) carefully as well as lighting. Fine crosshairs in low light can be difficult to use. Broad crosshairs against a small target are just as hard to use.
After you’ve figured out which focal plane you want the reticle in and what purpose you’re putting this gun to we can start figuring out if you need ranging capability and from there if you need advanced features like hold-overs and hold-offs and if they need to be in even intervals or not. If you don’t need ranging capability, don’t get it. It’s just a distraction in the image if you’re not using it. If you don’t need BDC, don’t get it. If you need a target dot, get one. Below is a list of some of the reticles of my scopes and what guns they’re on and some of my reasons for choosing them. These are representative of the world at large in most cases and will hopefully provide some context.
Woods Big Game Hunting Rifle, .30-06: <1960 Weaver K3 3x fine crosshair.
I use this for hunting in dense woods for deer, elk, bear and hog. Low magnification and a fine crosshair make for a rifle easy to use in bright light but not so much in low light. I walk hunt when I hunt the woods so I don’t spend much time in low light.
High Power Metallic Silhouette Match Rifle, 7mm BR: Weaver T24 24x44mm AO fine crosshair & 1/8MOA dot.
Super high magnification (24x), fixed power and adjustable objective with target turrets. The thin crosshair helps me avoid canting the rifle. The target dot makes for instinctive trigger pulling when the dot covers some section of the metal target. Silhouette competition is done standing up without shooting aids like glove/jacket/sling and we have to knock the target over so a hit anywhere on it is all we really care about. Super high magnification helps me keep only 1 target in the scope at a time. Lots of downsides makes this a bad choice for a beginner and a catastrophic choice for things like deer hunting in the woods. This is not for everyone but is popular in target sports. They’re super popular with long range varmint hunters as well.
Long Range Precision Match Rifle, .223rem: US Optics ST-10 TPAL MPR reticle.
This rifle is used from 200-1000m to engage metal gongs at known distances under time pressure. The MPR reticle has extreme flexibility in the reticle without getting to be a Christmas Tree. There are subtends in there that aren’t actually listed, they’re implied, and so this reticle takes a bit more training than a simple mil-dot system. Fixed 10x magnification is easy to use when scanning along a ridge line for concealed targets. I have also used a 16×42 on this rifle and found that that was often too much magnification when you’re moving from target to target.
Long Range Precision Match Rifle, .308Win: US Optics ER-25 5-25x58mm MPR reticle.
This is the big brother to my .223 match gun. If winds are too heavy for .223 I use this rifle. Having the same reticle as my ST-10 equipped .223 rifle means I have less to train for. The ER-25 is a 5-25x58mm while the ST-10 is a 10x37mm so the ER-25 is a FFP which is an irrelevance for the ST-10 since it’s a fixed magnification scope. Being able to drop the magnification on the ER-25 to 5x makes targets in the distance easier to find (greater field of view) and then you can just zoom in to 20-25x. 25x is too much magnification for most things so it rarely sees full magnification. This scope is best left to tactical and tacticool sorts of pursuits. This scope occasionally will see my big 7mag for shooting up to a mile against 2MOA steel gong targets but that’s mostly because it has the adjustment range and the magnification, not because it has the perfect reticle for that.
Plains Deer Rifle, 7mm Rem Mag: Vintage 3-9x37mm 30/30 Duplex FFP.
This rifle is explicitly for shooting at deer in open grasslands. Shots can be from 10yrds to 600yrds. The 30/30 reticle is a standard duplex reticle in the first focal plane. It’s meant to match a 30 inch width regardless of magnification which is about the same size that an adult deer is long from neck to butt. You can tell by what portion of the reticle is taken up by a deer about how far that deer is from you. It’s handy and light and gives a feature I find useful while having snag free low capped turrets, fixed parallax and an uncomplicated reticle. Uncomplicated scope, uncomplicated rifle, uncomplicated reticle.
Alpine Big Game Hunting Rifle, 7mm Rem Mag: Leupold VX2 3-9x33mm Duplex SFP.
This rifle is explicitly for shooting at deer in the California hills. Shots can be from 10feet to 500yrds. The duplex reticle is in the second focal plane. It’s just a basic rifle scope on a basic rifle. I find it useful to have snag free low capped turrets, fixed parallax and an uncomplicated reticle. This rifle gets walked over rocky terrain in high mountains so it needs rugged and simple with a crosshair that works high and low light and doesn’t needlessly obscure the image.
I was asked a question recently about shooting a firearm in space, specifically on the Moon but we’ll treat it as space generally and hit some specifics about the moon that are different. We’ll focus on normal “Earth guns”. That is guns that are designed to work on planet Earth within all of the environmental conditions present on the planet.
Shooting in space generally:
We’re going to ignore things like calibre, bullet weight and velocity and just focus on the most trivial bits here first. Shooting a pistol in space would probably not be very mundane but for a few microseconds if we assume that the weapon isn’t exposed to direct sunlight. It could get downright deadly to the shooter though. Space is not just big but super cold. It’s about the coldest environment you could think of. Not much of anything in the universe is much colder, especially if the sun isn’t shining directly on you. Assuming that it’s not then the gun is going to be something crazy like -400 degrees F and change.
At these kinds of temperatures the metal in the gun itself would tend to be very brittle and upon firing it would almost certainly explode unless made from an alloy designed to be flogged near absolute zero. The exploding pieces would be moving at approximately 2/3 of the burn rate of the powder and would certainly wound, if not chew up very badly, the astronaut as well as his space suit so he’d be hurt generally and exposed to the vacuum of space in short order and have his blood likely sucked from his body from any holes that managed to get poked in his skin. Perfect way to ruin a space suit and a day and a pistol.
If the gun was not in the shadow but instead exposed to the sunlight then the side of it that’s lit would rapidly heat while the other side soaks the heat. This would result in some parts of the gun reaching over 200 degrees Fahrenheit and other parts reaching -200 until equilibrium was reached. There’s no air in space so the cool side of the gun wouldn’t conduct and transfer the heat effectively to anything else which means the whole gun will soon be ridiculously hot. This will almost certainly cause malfunctions of the mechanism. Some parts would swell while others might contract. Slide rails and cylinder hands and all the little bits inside the gun that fit so tightly would begin to fit too tightly or not tightly enough and there’s a strong probability that the gun just would not fire. If it did fire there’s a near certainty of some kind of malfunction for anything semi-auto. Revolvers would probably fare pretty well though and single shots might be physically unaffected depending on how robustly they’re constructed.
If it did fire while sizzling hot then the ammo is going to be hot from baking in the chamber and you’re going to find a dangerously overpressure round as your first one and they’ll get worse as you keep (if you can) firing. Eventually you’ll see a kaboom and the brass case will open up and things will get 20 kinds of bad suddenly, very similarly to shooting the gun when it’s -450F and it explodes but this will be higher energy but also probably less destructive to the shooter. Metal is still pretty darned strong when heated to modest temps of a few hundred degrees and so the gun probably wouldn’t explode so much as you’d see the mag launched from the gun, the slide stop broken, a burst cartridge case and that sort of thing. The same sort of thing you’d see from a kaboom on a range on Earth. For a revolver, a loose cylinder gap could be utilized to accommodate the potential for large over-pressures.
Special ammo could be created that’s ultra-high temp compatible but because space is burning hot in the light and freezing cold in the shadow it would almost certainly be either very inconsistent or not very powerful. If something isn’t consistent you don’t want to make it very powerful. Makes hiding from the blast when necessary a harder thing to identify as being necessary.
There’s also the problem of inertia. In space proper, you hold a pistol and shoot directly away from you. Well, unless you’re braced against something that can provide counter thrust then you’re going to be pushed backwards away from the direction the bullet was launched. The bullet will continue forever in a straight line until acted on by a force like gravity or impacting something. So will the shooter. The bullet will move hugely fast but you will not unless the gun you were using was a howitzer. You’ll move backwards from your firing position at a speed relative to the total energy being projected. The bullet will get half and you’ll get half. So if the bullet has 300lbs/ft/sec of energy, so will you and you’ll move away at a speed reflective of that input energy which would be fairly slow even by terrestrial standards.
Shooting On The Moon:
So we’ve dealt with the bits of shooting while floating in space which is where the danger really resides. All of those problems are present on the moon. Light at 250F and dark at -400F is one thing. Micro-gravity is another problem of its own.
Apart from the fact that shooting a firearm on the moon would be a violation of international treaty it could be pretty dangerous too depending on the gun. Since gravity is weaker there the bullet will drop slower meaning if you’re not careful about weapon and ammo selection you might just shoot forward away from yourself and end up with the bullet hitting yourself in the back a few hours later. That would require a nasty fast bullet and is really borderline hyperbole but it’s still potentially true. The bullet’s maximum horizontal range – the distance it travels before gravity pulls it to the ground – is given by the equation:
R = v2 × sin (2a) / g
g is a measure of the strength of gravity. On Earth, it is 9.8 m/s/s. To find g on the Moon, we need another equation:
g = G×M/R2
G is the gravitational constant, M is the mass of the Moon, and R is the radius of the Moon. So, on the Moon:
g = 1.6 m/s2
Acceleration of gravity on earth is 9.81m/s/s. On the Moon it’s 1.622m/s/s. On earth with air resistance a bullet leaving at 3K fps will slow to 1.5K fps by .7KM and will have been flying for about one second meaning it’s fallen 9.81m (darn near 30 feet). On the moon it’d not slow down due to air resistance because there is none and so would fly at 3K fps (~1KM/sec) until acted on by something else to slow it down.
The moon being 10K and change kilometers around a bullet would need 10K and change seconds of flight time to make it around the Moon and hit you in the back if launched at 3K fps. This means that you’d have to launch the bullet from an altitude of over 1.6kilometers and then nearly 3 hours later be standing on the surface to get hit. Like I said, it’s possible technically. The bullet would not fling off into space. Even if you shoot it vertically, it’ll probably still be captured by the Moon’s gravity and eventually return instead of zinging across the solar system.
Truth be told, ballistics on the Moon is massively simple compared to ballistics on the Earth. The Moon rotates on its axis so slowly that vertical coriolis drift are essentially non-factors. Spin drift would also be reduced or nearly eliminated. Horizontal Coriolis drift would continue to be a problem because the Moon is still not a cylinder but instead an oblate spheroid. That makes it so there are really no straight lines when you engage in free flight over the surface. When you fire a gun on the surface of the moon you might get scooted back a tad from where you were standing but not far because there is some gravity there. Just enough gravity to be useful.
Once you’ve made it past the temperature and gravitational effects and the lack of atmospheric drag you get to the other problem: What the hell are you shooting at. There’s nobody there gunna rob you and you can be certain that if you leave your shit there that it will definitely not get stolen. There is also a distinct lack of any sanctioned firing range so the target practice excuse kinda kicks its legs up and dies.
Shooting on the Moon brings with it nearly all the problems of shooting in space (all of them that are problems because of a lack of gravity) and brings with it brand new problems unique to an environment with some gravity, though not much, and with all of the problems of heat/cold and a lacking atmosphere. The benefits of no atmosphere are to be had too. Consider what would happen to a groundhog on the moon if hit by a bullet from 10K kilometers away that was still going 3K fps. You think they fly into the air when hit with a .223 bullet still doing 2K fps after flying 400yrds across a field in South Dakota, wait’ll you see how high they fly when you hit them at 3Kfps from 10,000,000 yards and change. Betcha that surprises the shit out of them.
The ideal gun to shoot in space would be the Gyrojet. The projectiles fired are actually rockets and don’t have a lot of initial thrust (takes a few feet to get really sizzling) so recoil would be minimal and because they’re rockets meant to burn over a respectable amount of time instead of powder meant to burn more or less all at once the shooter is unlikely to be sent whizzing in the opposite direction with much energy.
May 5th 2016 marks the official launch of BallisticPRS. BallisticPRS is my new Density Altitude based ballistics spreadsheet. Just like its sister product, BallisticXLR, it uses the Pejsa model in the back end to do the calculations. Unlike BallisticXLR it’s meant very much for experienced shooters, particular those doing PRS shooting, that want field expedient printed data and a super simple system to create them.
BallisticPRS is implemented using Microsoft Excel (only genuine Excel is supported) and is massively simple to use. It provides drop, wind, movers, horizontal and vertical coriolis and spin drift data in 10m or 10yrds increments for every 500ft of Density Altitude between -4,000ft and +11,000ft. Data for each DA zone is contained on a single 8.5×11 size page and each page comes with a handy angle cosine table, compass rosette with cosines, conversion formulae and a mil-dot reticle subtend chart (there are dozens of other reticles already stored for easy update from companies like S&B, USO, Khales, Vortex, SWFA, Leupold and more).
As always, the download is free and I provide free email based support.