I was pretty surprised to see a 3-point jam in a Sig P320 (4.7 barrel, .40 S&W). The jam happened when I hand racked the slide to load the first round with a RCBS 10mm-200-SWC boolit (50:50 COWW:SOWW +1%Sn + 0.3%Cu). The brass case was deformed when the slide crashed into it. I measured the COAL after the fact and this one was 1.140 (book calls for 1.135). I had 10 rounds in the 14 round magazine, and the next 9 rounds all fed flawlessly. Brass was fired once before, in this same barrel. My next rounds will be 1.130-1.135 OACL, which I hope will fix this problem and meet the front driving band from touching the feed ramp. I cant afford to give up much on the OACL before I run out of case volume with this huge boolit.
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Ill give an update later as I figure out if this boolit will feed reliably or not. Max book velocity is 1,032 fps, so I really want this to work. 15 rounds in .40 S&W that matches .45 ACP energy & momentum is pretty attractive. My velocity at starting charge was 945 fps (True Blue).
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This picture shows where the tip off the boolit and the front driving band hit the feed ramp.
This picture shows the damaged brass and boolit, where the slide crashed.