Siringo wrote:Wildcatter -- you are correct in that the bolt seemed to be trying to open too soon. I have not shot anymore 400's, but as in my post, the heavier buffer seemed to help quite a bit.
I was using 25 grs of LG. Velocity was in the 1550 fps range. The heaviest charge I have used was 27 grs. That was about 100 fps faster and the rim bending was not as bad as with the lesser charges -- so your theory would be correct -- I got the bullet out the barrel faster to allow the pressure to drop before the bolt unlocked.
Ok, I really think you are way slow for that bullet. But, if you up the speeds, the thing will open the bolt even sooner, causing the rims to peel all the way off and things will get even worse, if you go to a slower powder, which you will need to do to proficiently up the speeds (My test are suggesting LG for medium weight bullets, the slower powders for the heavies and maybe even blue dot/2400 area, for the really light-weights, more on this latter this spring).
If I remember right you've got a 16" model. If you want to go to a rifle length gas tube, you'll need to block off the existing gas port, install the new rifle length gas tube, gas block, and of course drill a new gas port. To block off the carbine length gas port, any of a number of ways are exceptable. I my self, just turn the existing gas block 180 degress and reattach. Of course hand guard considerations must be addressed.
When you are working up the new load, possibly with slower powders, 296/1680, etc., it might be better to do this with out the new gas port being drilled in the barrel. Work up the load, without the port and then when you get the load you like, then drill a hole quite a bit smaller than .093, say in the .075 area, using a center drill to locate the first drill, just barely dimple the barrel, this will keep the small drill from wandering. Then, using the Numbered Drills, keep increasing the port size, one drill at a time, until the bolt holds open, make sure you are using the magazine and single feeding the rounds, looking for the bolt to "Just" hold open. At this point it is my rule of thumb, that after I the bolt/carrier is reliably holding-open, then increase the drill size, four(4) number sizes, now you are reliably working the action without over working it..
Hope this helps and spurs other thinking..t