Seating depths

[Sialan]

I have just fired the first shots out of my new Cooper MVT in 6BR & things look good so far. I used some loads roughly based on items on this site. I tried 60 GN Sierra HPs and 75 Vmaxs to start with in front of AR2208 and BM2,,your Varget & Benchmark respectively). The 60 Sierras shot 2 good groups of.257" and .320". The 75 Vmaxs didn't do too good until I got up into the higher velocity loads, one of them shot .380",These are all 3 shot groups. The tighter ones I will shoot 5 shotters with later to prove them up.)The 75s are mostly key holing but seem to start to stabilize as the vel. increases.The starting loads were BAD, 4" groups & badly keyholed. This is a 14" pitch barrel. My question is what seems to be the best seating depth ? If there is a best. I have seated all of these up into the lands but not hard. I have no previous experience with this calibre.

 

[SnakeEye]

Sounds like the 75 doesn't like the 14 twist. A 12 twist or faster would be better. Some 14 tw barrels will shoot them tho. The vmax seems to shoot better with about .010 or better jam, for me anyways. Also are you shooting over a chronograph, you need to know what velolcity you are getting.

Varmints For Fun

 

[Sialan]

Thanks for your comments. I have a chrony but didn't bother with it on the first day. But it will get used all of the time. As I said as the powder charge increased the 75 Vmaxs tightened up. The smallest they shot was still not a hot load just ADI's suggested max. The bullets were still showing slight signs of keyholing.
I will check the .010" jump as you suggest & work from there.