Meine Damen und Herren,

Much cogitation has sapped the consciousnesses of more than a few shooters when it comes to bullet-weight-variation and its effects on Point-of-impact, POI. To set my mind straight, I undertook a series of tests from the 1,000-yd line down at the Coalinga Gun Club back in 2004. Granted, the test was done using a BPCR; but, the results still apply to HP Silhouette, And, I might add, gravity is always on and it affects random vertical dispersion by the square of the bullet's time-of-flight. So, the BPCR tests from the 1K-line are much more extreme than a high-velocity, high BC bullet fired over just 500 meters. TOF for the BPCR bullets fired from the 1K-line is in the 3 second range. A HP round fired to 500 meters has a TOF of less than 1 sec. OK, I need to get some real results...back in a Flash, Jack...a 6.5, 140 A-Max launched to 2,800 fps has a TOF of just 0.694 secs when shot at rams, a 7mm, 168 SMK launched to 2,400 fps has a TOF of about 0.854 secs. To be clear, the effects of gravity on random vertical dispersion caused by bullet-weight-variation is not linear, that is, the BPCR bullet takes 3 seconds to travel 1,000-yds while the 168 SMK takes 0.854 secs to traverse 500 meters; so, 3/0.854 = about 3.5 times the effect, NO, that is not how gravity works. The actual effect is that the BPCR load is about 14 times more affected than the SMK load by bullet-weigh-variation with respect to random vertical dispersion, because random vertical variation goes by the time-of-flight squared.

So, here's the skinny. A method of casting "underweight" bullets was developed to cast lead-alloy projectiles for the test. When the bullet mold is bathed in a propane flame until all of the surface moisture is driven-off, high-quality bullets can be cast that will be underweight. As the mold warms from the hot alloy, the bullet weighs will increase. The result was that bullets that had a 5-grain range were used for the test. The "normal" bullet weight is 404 grains. It was launched from a 38-70 rifle sporting a 10-twist barrel. The powder charges were carefully weighed as well the brass properly annealed. The result, completely unexpected by this riflecrank, was that the target didn't care how much the bullets weighed. All bullets went into the same group from the 1,000-yd line.

Now, for BPCR's, carefully controlled powder-charge weights do have a substantial benefit in reducing random vertical dispersion at long-range.

So, the takeaway from that testing is, who cares if your high BC, high velocity bullets have a grain or two variation in weight, as long as they are not deformed.

Thanks for the good info Dan.

I agree with this completely. Also, another way to look at it is if you have a 7mm 168 SMK and it varies +/- 1 grain, you are looking at only a little more than one HALF of a percent of variation.

Add to that, I haven't seen any of my SMKs, Lapuas or Hornadys vary by that much. Generally I see more like a variation of 3/10ths of a grain. You are looking at a little less that 0.2% variation there. I don't see how we can realize that variation on target when shooting offhand.

Consider the effects of atmosphere and the variation of center of gravity vs. the center of moment. Rotational forces from a twist that is tighter than necessary ( that this faster than absolutely necessary to stabilize) just increase the disparity and destabilization of the the center of moment v. center of gravity conundrum. Additionally time in flight adds its issues. So a projectile that is traveling slow with a wide gap between centers (of moment v. gravity) yawing its way to vertical target from an steep approach angle probably won't deliver it energy efficiently....ain't that some bull Velocity will only increase the yaw although it may less the approach angle. Aside from atmospheric conditions ... those pesky targets tend to develop a bow which will deflect the projectile downward and not rearward enough....