Trom Bullets – Mythril or Myth

Joe from Australia sent me a question about Trom’s new plugs and I couldn’t help myself but to break out the calculator and start answering. I hope he’s a subscriber with a support agreement and if not, I hope he sees the light and buys himself a support entitlement so I can keep doing this kind of stuff. Suffice it to say that what we find is not what we expected.

Trom likes to bandy their bullets as some super special magical gold ninja sniper secret squirrel stuff but they’re very much not any of those things. Are they interesting? Yes, for sure on academic and martial planes. Evolutionary? Yep, to be sure, there’s some really cool technology being refined that someday may make a revolutionary change happen. Revolutionary? Nope, not at all. Wondrous and to be spoke of with awe? Certainly not. Not even remotely. Pedestrian? Nah, that’s a good bit too harsh.

You can tell it’s a brochur when it doesn’t tell you anything you weren’t expecting.

They’re actually kind of pedestrian in a few ways but, NOT all ways. The BC numbers discussed below are super interesting and are for argument’s sake only because they’re based on backing into BC numbers from drops and velocities. Barring the BC data though (which is in some ways extraordinary), these are exactly what we’ve come to expect of mono-metal bullets. Light for their physical size because there’s no lead core. Figuring out what was going on in the BC numbers… that was easy as pie for someone with a ballistics calculator they really understand and about 20 minutes on their hands. What it revealed was really very surprising but less shocking than it might have been if the effect were more pronounced. What effect? Read on.

The bullets produce (and this is very roughly arrived at because nobody’s paying for this so I’m not being super precise) exactly the kind of low BC’s you’d expect from a lead-free monometal bullet of the 135gn weight class. That trash BC is being made up for partly with a really high launch velocity which is enabled only by driving bands limiting bearing surface. So, BC’s are unsurprisingly low and velocity of launch is VERY high and the resulting trajectory matches very closely with M118LR 175gn SMK loads as a result. I can smell an answer to an unasked question looming on the horizon.

Cutting Edge Bullets… not a brochure but instead, straight unemotional facts.

Normally launching mono-metals super fast leads to pressure problems because those lead free bastards are so bloody long and long bullets generally means longer bearing surfaces which means friction which means pressures. These Trom bullets seem to be, if not inspired by, at least very similar to some other projectiles from DSG Technology that have made their way into testing with the US military. Those have a not very clearly evident wasp waist with some very interesting curves to it and some very deliberately and unconventionally shaped driving bands. Subtlety really makes those DSG pills interesting (see image below).

The secret sauce from my view and the truly academically interesting thing about Trom’s .308 135gn bullets is, their G1 BC actually increases a good bit as velocity decays and velocities for a monometal bullet of this mass are extremely high. This is likely due to their driving band shaping & shank and heel geometry leading to a much reduced drag coefficient at lower velocity regimes and also must have something to do with ogive shaping. My hunch is that they’ve leveraged something like a pointed Von Karman nose design with a custom designed live curve to it, a wasp waist, assymetric driving band geometry (think 5R rifling technology applied to a driving band) and optimized driving band layout (spacing, number, location, etc…) to create a turbulent flow area around the rear of the bullet shank from the center of gravity back to a very mildly tapered, if tapered at all, heel that’ll be close to a flat base if not an actual flat base. With the flow already turbulent, there’s a huge decrease in drag. How they’re getting turbulent flow to stick close to the bullet base itself I’m a little curious about. The curves near the base of the bullets in the pic below tell me a lot about how those are being meant to work but it seems like those would increase laminar flow which will increase drag if it’s allowed to contact the base of the bullet in laminar flow.

DSG projectiles. If you look closely you’ll see some angles that you might not expect at mid-nose and ogive and abrupt heel section with a notably lacking boat tail. Boat tails are a double edged sword sometimes.

It is important to note that G1 is a form factor based drag model, which these Trom bullets are not represented well by. It’s also important to note that the head dude over there said in no uncertain terms that doing something like I do below is not only impossible but not useful. I would care to dispute the living shit out of that. Banding isn’t perfect, it says that the model has an error and we’re setting a limit because we’re trying to not approach that limit too closely, so we use bands as the limiter of the error magnitude. That’s why the banding is necessary at all. While I can (and did) derive G1 numbers in bands which seem to generate drop numbers that match the manufacturer’s numbers, I didn’t go to great lengths to be extra precise because I was making the point that he either didn’t know what he was talking about with respect to the existence of and possible methods of use for the Pejsa-Mayewski G1 model that forms the basis of BallisticXLR or that he was being deliberately dishonest. I wouldn’t believe the latter in this case. That said, there’s a lot of something in their product descriptions:

So, are you ready for some fact-heavy truthiness? Using the numbers below will get the shooter to within about 2 clicks of dead on at any range having a velocity of 1100fps or more (900yrds) and I was able to easily track it to match advertised values out to 800fps remaining velocity (1100yrds). After that I got lazy. Trom reports fantastic performance in the transonic zone which I’ve gotten only second-hand information about and I have not seen any direct evidence beyond some marketing oriented brochure style dreck. Here’s what I get for G1 numbers based on advertised drop and velocity data.

G1 BC’s Trom 135gn .308 @ 2885fps MV:

Velocity Minimum G1 BC
1900fps .28
1600fps .35
1100fps .38

So that’s all the good stuff and the way I’m betting it works. I don’t have any to analyze and I betcha Trom will tell me to get fucked because my goal would be to shatter any marketing hype and present facts dispassionately.

  1. The 135gn Trom .308Win loading is handily matched by the good old fashioned M118LR using 175gn SMK’s at 2600fps.
  2. M118LR delivers more energy at all ranges and an almost identical trajectory while providing greater sectional density (meaning better penetrative capacity).
  3. The Trom bullets suffer from a massive initial velocity decay rate due to the lack of mass affecting the real BC negatively.

The only benefits to the Trom stuff I can see is that on a 200 round combat load-out the carry-er saves just a hair over half a kilogram of load and there’s no lead in the bullets so they’re useful for hunting in the California Condor habitat zone in California (no lead allowed). They’re otherwise looking like a gimmick with some real, but unrealized, potential.

When you look at their advertisement materials you might notice the use of special definitions of “Maximum Effective Range” or MER. A rifle’s maximum effective range is the maximum distance where the weapon may be considered to be both accurate enough to engage the target at hand and powerful enough to be capable of entirely defeating that target. In military circles the accuracy requirement is for 50% of rounds fired to impact a particular standard target at the tested distance. For our purposes right now as civilians we’re using hoards of deer, overbearing government officers, and lawless British tea importers as the hypothetical targets.

One important factor is that many bullets destabilize in the transonic zone which destroys accuracy and shuts off the “effective” part of MER for them early on. I break things into 2 levels… Maximum Effective Range and Maximum Dangerous Range. One is about defeating a target utterly. The other is about trying to not defeat a non-target inadvertently. That means you have to compare apples to apples and not cherry pick an orange that is explicitly meant for 0-300m use. I use a .30Carbine at 300m VERY effectively and up to 500m I can still make a man sized target very concerned for its safety. A .300BLK is no real advantage to me there. They should otherwise be thought of as very much the same class of weapon. Short range, with just a little more poop than a pistol. What you get from the .30carbine that you don’t from a .300blk is the energy dump is in the core of the target body, not inefficiently burned mostly at the surface.

If you could literally navigate a specially designed bullet’s crossing from supersonic to subsonic you’d maintain accuracy by making sure the center of pressure is always moving true into the direction of flight without large departures in the angle of repose and then to have enough power to defeat a flesh & blood target at the end of the flight. Flesh and blood are fragile as hell and don’t respond well to bullets.

Most things in here don’t respond well to bullets. – Capt. Ramias

Nothing in here responds well to bullets. – Slim Goodbody

So the argument they make that .300BLK is commonly effective only to 400m is based on the bullets being used in those loads being SPECIFICALLY MEANT to be used really from 300m and in. If they use a bullet meant for longer times of flight and transonic stability (ok, like the Trom bullet) so they retain their original cone of fire dispersion without increased dispersion inside or after the transonic zone they’d be effective out to any distance they’re still capable of inflicting a lethal wound at, which would be easily up to 900m or substantially further against a meat target. It doesn’t take much for a bullet to be lethal but this kind of “well it’ll do this one thing marginally but it will do it” thinking is nothing short of me saying that because I’ve made a sequential pair of hits with a .22lr at 1500m, that my .22lr Ithaca X5 rifle is effective to a mile. No. It’s dangerous to a mile, I’m effective to a mile. Important difference.

What Trom has done is take the military rating of .300BLK of 400yrds; I guess because that’s where the supersonic 147gn loads go transonic and flip out, and simply decided that as their ammo is stably transonic traverse capable that it’s “effective” to 900 yards where it would have something very similar to the energy and velocity and bullet weight of a 9mm at the muzzle. Sorry, that’s just not going to cut it. Just because you might nearly reach some goal doesn’t make you effective at attaining it.

For my purposes I set a floor of 500lbs of energy for non-predator (a predator has teeth and claws and is not an omnivore) animals in the 100-300lbs class. I also don’t consider penetration of the transonic region to be characteristic of a modern high velocity rifle that is being used effectively. If the bullet starts at or near transonic like some .22LR, heavy 9mm’s, heavy .40S&W’s, most .45ACP and other low power arms then it’s meant to be used at distances where the bullet is more or less still transonic (.8mach – 1.2mach). If it starts out subsonic then it’s meant to be subsonic when it hits its target. If it starts out supersonic then to my mind you really want it to impact the target at supersonic velocities or at the very minimum just as it starts to tickle the high end of the transonic. When we stopped using black powder rifles as primary combat arms we stopped needing to penetrate the transonic region basically at all. Black powder can only get bullets moving just a bit over supersonic so we’d use HUGE projectiles in them because there was no limit to mass and we’d get them just into early supersonic and shoot them with the intention that they’d be transonic or even subsonic at impact but be able to defeat the target because of enormous momentum from the giant projectiles being used.

500gn bullet at 1400fps, good to a mile. Massive bullets were needed to carry energy since maximum burn velocity of black powder is kinda low.

So what has Trom done in the marketplace? They’ve not been entirely clear with their potential customer base. They’re being businessmen first rather than members of the shooting community. Trying (obviously too) to hype the hell out of something that’s otherwise not much more than spitting distance from plain-jane to reap the maximum ignorance-sourced cash flow is unethical in my view. They’ve made claims which are simply spun talking points that ordinary folks can’t discern from unbiased truth. They’ve used some customized facts and careful phrasing and massaging of definitions and done their level best to obfuscate an otherwise pretty unexciting truth of the matter and completely ignored the ridiculously exciting part. Instead of trying to market a sow’s ear to Tiffany & Co purse customers, how about just noting what you actually get which is substantial: An increasing ballistic coeffiient. It’s in the shape so ditch the light monometals and get with the lead programme. Give us some flat base bullets that we can run stupid fast and that has an increasing BC.

Here’s a trick: When my .50cal black powder rifle doesn’t reach far enough with enough energy to defeat a tank, I don’t redefine the goal as defeating a jeep and then congratulate myself on having achieved it with a .50cal black powder rifle. I pick a different gun and defeat the tank.