So, when Sierra announced their new 20-caliber bullets, I was most interested in the 32-grain version, for the same reasons. However, preliminary testing with these new bullets in a 1/12 twist barrel of proven accuracy potential demonstrated that the lighter Sierra bullet was evidently not up to the stresses imposed by launches in excess of about 4400 fps. While, the 39-grain bullet showed exemplary accuracy – I am confident that I can find a combination that achieves 4200 fps with five-shot groups consistently in the 4s or even better – the 32-grain bullet produced patterns – groups in the 1½ MOA range were the best I could do.
For this reason, I was most anxious to test the 32-grain Sierra in the 1/16 Pac-Nor barrel that Chris Dichter had send me. This twist will not stabilize any bullet heavier than about 33 grains but it is reported to work well with lighter bullets, which are what I am most interested in.
To date, I have only been to the range twice with this barrel to test loads using the 32-grain Sierra in the 5/35 but the results are encouraging. The load that looks most promising is a top-end BenchMark charge with the bullet seated about 0.020-inch off the rifling. Muzzle velocity exceeds 4650 fps with a standard deviation hovering near 10! Accuracy of the one five-shot, 100-yard test load at this overall length was well under 0.4 inch, on centers. Other loads tested at similar lengths provided sufficient accuracy so that I am encouraged that I can probably find a combination that will routinely beat the one-half MOA standard, which I consider to be sufficient for a 400-yard prairie vermin combination.