02-09-2015, 03:25 AM
Tman, here's one purely empirical data point for your consideration. My barrel is a 20" 1 in 9 twist. I loaded up some 140 gr Berger target bullets today. I know 140 gr is outside of the Grendel's boilerhouse, but they were available and I like Bergers.
The first 3 groups were kind of all over the page (up to 6") and keyholed most of the hits. My final group was Berger's max load. At this higher velocity, the holes were perfectly round and it put two in the same hole with the 3rd about 1.25" away. Berger's manual (and the link above) recommends 1 in 8 twist for those bullets, but I wanted to try them anyway.
The first 3 groups were kind of all over the page (up to 6") and keyholed most of the hits. My final group was Berger's max load. At this higher velocity, the holes were perfectly round and it put two in the same hole with the 3rd about 1.25" away. Berger's manual (and the link above) recommends 1 in 8 twist for those bullets, but I wanted to try them anyway.