Jerry,
Are you suggesting in fact, he had next to no neck tension?
So that variable was somewhat removed
You have got me to thinking, we use a powder which is readily available here, ADI, Benchmark 2. Other powders are available but nearly double in price.
We have an old Stolle LV, 6 PPC with .262" neck, and it is owned by my friend, for years we have been thretening to toss the barrel, it makes a good spare barrel if another friend wants to come out for a shoot. We think it has fired close to 2500 rounds, it runs no neck tension, as my friend is too cheap to buy a smaller neck bush, when you load it you have to pull the bullet forward than insert it in the breach. just in case the bullet has fallen into the case!
Surprisingly it can shoot as well or better than our much prized BAT SV LV set ups. In this case, with the powder we use, it does not have a negative effect on accuracy!
Good Shooting!
Jim