Best bullet design for long throat/freebore?
I decided to start a new thread with this specific question.
I have currently two guns with very long freebore. A 270 win with about 400 thou and a Weatherby 340 with easily 600 thou.
I cannot come anywhere close to the rifling on either rifle, and whats more, I observe that in the case of the 340 Wby, the bullet has LEFT the case neck before it has engaged the rifling, with both my recently acquired 250 gr Bergers and Nosler 225 Accubonds.
I have read that this latter scenario is a real NO-NO. The bullet is truly allowed to "skew" in the throat, potentially even allowing hot gasses to pass around the bullet till it seats into the rifling.
Interestingly, the 340 Wby shoots factory 225 Barnes TSX bullets BADLY, with 3" groups. When sent back to WBY, they shot it with 200 gr spirepoints and got a 1.5" group. Told us it was within factory spec, and we should use 200 SP bullets. Nevermind they are no longer in production.... The 340 shoots the 225 Accubonds very poorly as well. The 250 Bergers have not yet been tried.
We did shoot some factory 250gr Partitions (flat base) in the Wby. They shot under 1.5" as well
Another observation, perhaps unrelated to throw into the mix, is that my long throated 6.5x55 also prefers flat base bullets. I never bothered to measure the throat on the old swede, cause I know its a long way out there, and I have to keep COAL short for the magazine. But, now, in retrospect, I am suspicious that my troubles with the swede and boattail bullets may be related to the same problem I am seeing with the Wby -- a very long throat.
So here is my theory: When working with a long throated gun, it is VERY important to make sure that the bearing surface of the projectile is still in the case neck when it contacts the rifling, and since boat tail bullets have reduced bearing surface, they may be a poor choice for accuracy.
Moreover, if the gun has sufficient magazine length, or you are willing to hand feed, a flat base bullet can be seated further out than a boat tail of similar weight, getting your ogive closer to the rifling and potentially reducing some of the negative effect of the long freebore on accuracy.
Could I be right?