How To Use Ballistic_XLR: Table 100
Table 100 is designed to provide a single page with all the data you need to get your rifle on target out to 1700m. Beyond 800m most rifle rounds are going to be coming down pretty sharply and it’d be better to use Table 10 for your data. This gets into danger space and swept space and if you’re not familiar with those please watch this before deciding to use the Table 100 data instead of Table 10 data:
Now, provided that Table 100 is suitable to your needs the usage is pretty straightforward. The table is keyed for your normal station pressure and includes wind and drop deltas for -1inHg. The reason for that is, it’s not entirely unlikely that you’ll have a hill to climb or descend or that one day could be cloudy and cold while the previous day might have been warm and sunny. These are barometric pressure changes that need to be accounted for. Those data are there to be used and they should be used by subtracting the values listed in those blocks from the data you calculate AFTER your final firing solution has been calculated. The reason to do it afterward is just to keep all these numbers from confusing the hell out of you (and me).
I mostly use Table 100 for hunting purposes or informal target shooting where first round hits aren’t a priority. I also use it at High Power Metallic Silhouette matches at ranges I haven’t been to before to get my initial DOPE settings (these get refined during the sighter period before the match). I do not use it in competition unless the way the match is shot doesn’t lend itself to using Table 10.
Moving on: Let’s assume we’re proned out behind the rifle and we’ve got the 12×20″ iron maiden target on-sight and ranged using the mil-scale reticle. We range the target at 815m. First thing first, it’s not at an increment of 100m. Assuming a 6.5×284 performing at 2900fps and coin with a 140gn slug, we look up our 800m elevation and see 5.65MRAD in the 800m slot at our temperature regime. Above that we see 4.55 at 700m and 6.85 at 900m. This means that over this 300m range we’re adding approximately .1mrad per 10m. This is called interpolation and that’s how it works. It’s nothing but simple quick averages. 800m indicated 5.65 + 15 yards worth which would be about .15 we’re at 5.8MRAD elevation. Write that down somewhere or just enter it in your calculator (or head).
Now we need to finish elevation. That happens at vertical coriolis. So we look at V-Cor for 800m we get .05MRAD being full value. We need to get our compass heading now and find that we’re pointing 10deg north of due East. We need to find our degrees away from North from that and we find that it’s 80deg. Look now at the compass rosette and find the 80deg mark near the East point. The cosine is just outside the rosette for each bracket of angle.
In this case the cosine is .985 which is close enough to full value and full value is so small that we’ll just take the full value number and (because we’re facing East) subtract that from the elevation setting for range (for westward shots you add the V-Cor value to elevation). This gives us 5.75MRAD and if we round up we end up back at 5.80MRAD.
Now to the windage correction. It is vital to keep track of which direction you’re adjusting windage since it will get adjustments in both left and right in many circumstances. If you lose track of which direction things are moving then you need to assign little arrows or something on your calculation sheet or find a way to keep that data sane. Windage is the source of most misses for the new long range shooters and seasoned ones that I play with in the real world. Assuming that you’re going to dial for wind and not hold for wind (holding wind is arguably better for a number of reasons but beginners should learn to dial things and hold steady until they can read the wind a little, then start holding off for wind). Also realize that windage and wind are different words. Windage refers to the adjustment we put into the sighting system and wind refers to the air moving.
Get a wind reading in whatever way you can. If you’re at ground level and using a meter like a Kestrel then you should verify that reading against flags, trees, brush, mirage, etc… Why? Well because of the way air moves over the surface what we end up with is lower wind at ground level than at 10m. Similarly when you fire from 10 inches off the ground at a 800m target you’re looking at the bullet being 4ft or more off the ground at the maximum ordinal. Wind will be stronger at 4ft than at 10 inches.
We take a wind reading and look at the range flags and we’re seeing the Kestrel read 7mph and the flag is showing 10-12mph. We’ll call it at 10mph for simplicity. Look up the value on the windage sheet for our temp regime and we get 1.54. The wind isn’t directly against us though, it’s coming from 5 o’clock so we look at the compass rosette and get the cosine for winds coming from 5 o’clock (so wind is to the left) which is .5. So we multiply that cosine by the indicated wind adjustment and get .77MRAD right. Now find the Horizontal Coriolis which is always full value and requires an adjustment to the left in the northern hemisphere and we get .2MRAD. Since one is to the right and the other to the left we subtract and get .57MRAD right.
Look over at the Spin Drift which is always full value (and we’ll assume left adjustment from a right twist barrel) and we get
.13MRAD left. So subtract .13 from .57 because they’re opposing directions again and we get .44. Round that and we get .4 right total windage.
Now for the fun part, dial 5.8MRAD of up and .4MRAD right. Hold center of the target, get a natural respiratory pause and let fly. Wait the 1.1 seconds for the bullet to get there and another 2.5 seconds for the sound of the impact to get back to you (via distance-in-ft / 1050 = time of sound propagation) and revel in your awesome. You can even use the time of flight chart to figure out the time it’ll take for the bullet to get there, how long before the target hears your rifle boom, how long between the bullet strike and the target hearing the boom and lots of other fun and tactically interesting uses.