Originally Posted by Any Cal.
I've read that quote, but have seen things work differently several times, so don't think it holds water. I also don't see how it is physically possible for the breech to open under pressure unless the extractor overrides, and then you would have a jam-o-matic.
In my food for thought thread in the 10mm reloading forum, sd dropped quite a bit with heavier loads. In the 10mm recoil spring video there was no clear trend either way using hot ammo. If the breech caused the velocity swings there should be some sort of indication in the brass, like it stretching .1" or a bulged casehead or a broken shell, since we are talking about the slide retreating a significant amount while under pressure.
A better test would be one that showed sd dropping as you went from firing without recoil spring, to stock spring, to heavy spring, to holding the breech closed, or at least a clear delineation between inadequate and proper support.
Thanks for the feedback Any Cal. You may be correct. One way to exclude the auto's operation would be to try them from a revolver or rifle or do what these guys did: http://www.ballisticsbytheinch.com/10mm.html
I have been chomping at the bit to chrono a bunch of 10mm loads, but it's tooo difficult/impossible for me to do at the range, so I need to get on some private land. The only BB loads I have chronoed was their 360gr .454 loads out of my 7-1/2" FA. I shot five rounds, and they all were between 1,488 & 1,503 fps. Perhaps that was a fluke, but if not, I would be interested to see whether their 10mm loads are as consistent.