Since the "smooth" version of the control load had shot surprisingly well on January 13, I decided to try a couple more versions of the control load.
The uncoated version of the 180 gr. BB did "OK." If you disregard the one wild flier, the average group drops to 3.53", practically the same as the control load's 3.52".
However, velocity variation was significantly worse than the control load -- 67 ES uncoated vs. 43 ES coated, and 1.8% SD uncoated vs. 1.3% coated. Bear in mind that these loads were not crimped. The no-crimp loading worked satisfactority with the coated control bullet, but it's possible that the uncoated bullet is more slippery and would benefit from a crimp?
FYI there was a 5 - 10 mph wind quartering across the range when these groups were shot, and that may have contributed to the horizontal dispersion in two of the groups.
A borescope inspection revealed no leading with the uncoated bullet. At the beginning of this project there was light leading with uncoated plain base bullets, but that was in a different barrel with a different forcing cone and a different bullet. My guess is that this barrel's improved alignment and improved forcing cone are responsible for the reduction in leading.
The unlubed but coated version of the control load did not do well. Perhaps it was the shooter's fault or perhaps it was the 5 - 10 mph wind quartering across the range, but the unlubed bullet did not even try to shoot nice groups. I have no explanation because the smooth bullet was also unlubed yet it shot OK. Summary of results:
-- the uncoated bullet had worse velocity variation, while the other 3 were about the same.
-- the unlubed bullet may have had worse accuracy while the other 3 were about the same.Recent lessons learned:
-- reducing the jump to the rifling by adding a 0.357" band at the tip of the nose did not help accuracy.
-- this particular barrel / cone combination does not lead with plain base bullets, at least not at 26 ksi.
-- it did not like the Keith designs, but I can't explain why.
-- accuracy was mediocre with the the bevel base bore riding design, but I can't explain why.What's Next?
-- do an alloy shootout with the 180 gr. BB control load, using both coated and uncoated bullets.
-- try a GC version of the 180 gr. bullet? I have tried GC's previously but so many things have changed since then.
-- try a smaller meplat?
-- try 300MP powder? It may be too slow to hit the desired velocity, but the slower burn rate might be gentler on the cast bullets.