papajohn wrote:DANG Hoot, that's pretty darned impressive. If I ever grow up, I wanna be just like you!
Does this mean that load development with that bullet is pretty much over?
First off no you don't want to be just like me, but there are parts worth emulating. Other parts have no scrap value and a few are classified as hazardous waste.
No, I may try some over IMR4227. Given the swiping and primer flattening, it may be going in the wrong direction. I have to admit, the recoil impulse from W296 was a little less sharp than the Lil Gun but the overall energy was about the same. Swiping is most often when there's enough pressure presented to the gas port to begin cycling the action before the pressure has dropped enough to not push the case out too hard. You want the case to be pulled out by the extractor with a little help from the residual pressure. In this test, I don't think that was entirely what was happening however. There is such a thing as so much pressure that it pushes the case back regardless of whether the action has begun cycling or not. When that happens, and the bolt begins rotating out of lock, you get a shorter (as in my case) swipe but scratching deep enough to raise a slight burr on the leading edge. I didn't see any imprinting however, so those are conflicting observations. There's a final cause of the kind of swipe I saw and that is not only are the pressures high, but in the case of W296, it took longer to get up to pressure (burn rate) than Lil Gun. There is a correlation to the rate of pressure increase and how tightly the case locks to the chamber walls before being acted upon by the pressure trying to push it back. Again, the culprit is a slightly slower powder as in the relationship between W296 and Lil Gun. Lastly, there are less likely contributors but I've already gone into enough detail to have to digest.
Perhaps, instead of using IMR4227 which I believe is more appropriate for 300 grainers, I may try some of my Aliant 300 MP. IIRC, it is ever so slightly slower than W296 but faster than IMR4227. Going the other direction, I may try Lil Gun again, but a step or two (or three) lower charge than I did in this test. Even knowing that the Brass bullets are slipperier, I'm not comfortable with any load that kicks 245gr bullets out the barrel at 2400+ fps in an AR platform. The Bartz is a beefy built action and less robust ones may not tolerate that kind of pressure = velocity. I would consider 2400+ fps more appropriate for bullets in the 200-225gr range, again in an AR platform. With the pull-downs, I'll have enough bullets to run several different experiments and God knows, I love experimenting.
Note: These loads I worked up are not appropriate starting points for a 1:16 twist bolt action, despite its edge in strength over an AR platform.
Sorry for the windy response.
Hoot