People maybe now have access to a new tool in determining this BC v LR stability balance - electronic targets giving terminal speeds and ES/SD data for strings. There is a thread somewhere on the forum that followed the use of Silver Mountain e-targets at Lodi for the US FCNs in 2017, their first major event outing in the USA I believe, and it has a very interesting post from a competitor who used both 223 and 308. Having suffered problems with his 308 he had to switch mid-tournament to 223 and found that despite starting with very similar ES values at the muzzle for the cartridges that the 223 terminal speeds ES at 1,000 (shooting 90s IIRC, but cannot be 100% certain on that) was double that of the 308. This struck me forcibly at the time as significant in that the 223 with 90s is known for elevation fliers at long ranges and there has long been a suspicion that these bullets' stability lack 100% consistency so that a small minority generate different levels of drag from their fellows. The e-target data appeared to support that hypothesis.
So ..... if there are doubts about whether some bullets 'work' at 1,000, I would suspect that similar problems could well show up on the e-targets' retained speed ES / SD sizes. If all 20 rounds in a match are recorded as being within the same size of range as those from bullets known to be very stable and consistent LR performers, that would suggest that any problems they have are not as a result of variable stability. Any increase in yaw, precession etc should increase drag / reduce terminal speed.
Of course, if every bullet were to suffer the same amount of yaw and increased drag, the terminal speed ES could still be apparently satisfactory. However, given mutters about some models behaving inconsistently that outcome seems very unlikely, and even if it did apply, the effective average BC would be affected across the board.
Laurie - I would think that using consistency of ES/SD at the target as a measure of stability and by extension, precision, would depend almost wholly on the exact cause of any instability that might be observed with a given projectile. If instability was evidenced soon after exit from the bore (i.e. typical pitch/yaw), you can easily envision that it could create measurable differences in ES/SD values over a 1000 trajectory. However, if the instability was due to some other factor that didn't materialize as a significant factor until late(r) in the trajectory, there may not be sufficient travel distance remaining to create a noticeable difference.
I point this out because over the years, I have observed numerous references to "abnormal" ballistic behavior from the 90 VLDs at longer distances (800+ yd). Having fired many thousands of rounds of 90 VLDs, I have never observed any phenomenon that would lead me to believe the 90s start behaving erratically at some distance past 600-800 yd. Further, it is beyond clear that they can perform extremely well out to 600 yd, as numerous F-TR shooters have found in MR matches over the years. Together, those two observations would suggest that there are unlikely to be any unusual and significant instability issues with 90s straight out of the bore. If there were, it is unlikely that it would show up only after 800 yd or so.
Along that line of reasoning, I can imagine a couple reasons why you might observe greater ES/SD values with 90s at 1000 yd than with a high BC 30 cal bullet. The first would be that they generally start out with much greater ES/SD than good .308 Win loads. In my hands, achieving ES values of 10-15 fps with .308 loads is usually not too difficult. In contrast, I rarely observed ES values like that with 90 VLDs loads; more typically 18-25 fps (or even slightly more) ES values are the norm. I attribute this in part to the fact that the case volume of the .223 Rem is just over half that of the larger .308 Win case. Even small variance in charge weight, case volume, neck tension, etc., would be predicted to have a much larger effect on velocity.
The second possible reason is merely speculation, nothing more. I point that out because, as I mentioned above, I have never observed "anomalous" behavior from the 90 VLDs from 800 to 1000 yd. Nonetheless, it is possible there could be some design factor inherent to the 90 VLD that renders it less stable, or perhaps, more "sensitive", to external factors, but only after it has traversed some minimal distance (i.e. 600-800 yd). Such a factor, if it exists, would be akin to the dynamic instability caused by the boattail design of the 168 Matchking, in that it has a negligible effect on precision at shorter distances, but shows up quite readily at distances past 600-700 yd, or so. As I mentioned, I have never personally observed such behavior from the 90 VLDs, but acknowledge it as a possible explanation for certain behaviors others have reported.
The only other observation I have that might deserve mention at this point is with respect to the latest generation extremely long, short bearing surface, high BC 30 cal bullets such as are the topic of this thread. I have talked to a number of individuals that have had similar experiences to mine in terms of tuning loads with these bullets. The bottom line is that some aspect of their behavior seems very different than other bullet designs. Despite significant effort, I have been unable to find a consistent tune. I have fired plenty of groups where you might put two or three in a row into the same hole, all of a sudden, one shows up 3/4 of an inch out of the group, at a distance of ~100 yd. There is no apparent rhyme or reason for this: velocity data appear normal, the rifle has a sufficient twist rate (9.0) and shoots quite well with other bullets. Basically, I am at a loss to explain the inconsistent grouping, other than as some possible design factor inherent within the bullet itself. I don't know if you can call this a "stability" issue, per se, but they are apparently not all flying consistently straight out of the bore. As you can imagine given the inconsistencies, I would not attempt to shoot them in a match at this point. I mention this behavior only to compare/contrast it with observations regarding 90 VLDs at 1000 yd. My impression that the two behaviors are completely different in that I've never had a problem getting the 90s to print tiny bughole groups.
) And .... I increasingly rely on Viht N100 series powders whose lot to lot consistency is very good indeed. BUT ... even so, I'm always very reluctant to rely on a load where some minor variation or other can push it into producing three quarter or even MOA verticals.
