RCBS 10mm-200-SWC Jammed a P320 .40 S&W

[justindad]

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 can’t afford to give up much on the OACL before I run out of case volume with this huge boolit.
*
I’ll 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).
*
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.

[GooseGestapo]

Check your sized diameter and brand (head stamp) of brass.
Looks like not enough clearance in the chamber.
Try sizing smaller and seating slightly deeper.

[justindad]

My 2nd batch of rounds resulted in 1 out of 40 jamming.
Changes from first batch:
1. Virgin Starline brass (vs once used Starline)
2. OACL is 1.132” +/- 0.002”.
a) previous jammed sample was 1.140”
b) jammed sample from this batch is 1.132”
3. Crimped slightly tighter.
4. True Blue powder worked up from 5.8 to 6.4 grains.
a) Fired cases with 6.3 grains passed easily through the Redding bulge buster.
b) Fired cases with 6.4 grains took a lot of force to go through the bulge buster. Gave 1,008 fps & SD=4 from a 4.7” barrel.
c) Bulge was present in the web, not higher like a Gen 4 Glock 22.

[justindad]

My 3rd batch will consist of these two options:
1) RCBS #10mm-200-SWC
a) 1.125” OAL
b) Cast boolit length is 0.717” as-cast (50:50 COWW:SOWW + 1% Sn).
c) 5.7 grains True Blue
Note: GRT says 5.7 grains @ 1.125” gives similar pressure to 5.8 grains @ 1.135”.
2) Saeco 047 200 grain TCBB
a) 1.135” OAL
b) Cast boolit length is 0.702” and weighs right at 200 grains as-cast (COWW + 1% Sn).
c) 6.0 grains True Blue
Note: GRT says the Saeco boolit at 6.0 grains gives similar pressure to the RCBS boolit at 5.8 grains.
*
The two reasons for the Saeco boolit are:
1) Smaller meplat, which is good for feeding.
2) TC instead of SWC, so no shoulder to snag on anything while feeding.
*
RCBS (1) on left.
Saeco (2) on right.


*
Here is a picture of the 2nd jam, which was not as severe as the first. It does not appear that the ejector claw is grabbing the case rim soon enough. I have had no jamming issues with a 175 grain Lyman #401638 boolit (1.100” OAL), nor 155 grain & 200 grain Hornady XTP (both 1.135” OAL).

[popper]

No crimp? Or optical illusion. Do they drop in and out of the barrel OK? Seems like they need to be deeper. My 165 & 180 TC seated just with a smidge (maybe 20 thou) of band sitting above the mouth work OK. TC hits top of chamber and slows down cycling. Not familiar with that mold but if the meplat is larger then the TC part angle is different. Yup, looked at the pics, meplat is much larger. You may need to seat with the body entirely in the case.

[justindad]

There is a taper crimp, but just very slight. I loaded the 3rd batch and left town. I’ll try to remember to get a pic of the crimp before I shoot them. Still gotta do the plunk test and these latest rounds.

[softpoint]

I have that same RCBS mold. I load it in two different 10mm autos. I load it flush with the front edge of the band. I haven't had any trouble with it either in my Glock or my custom 1911.

[justindad]

Turns out to be the gun, not the ammo. The issue exists on the full size (4.7” barrel) and not on the carry size (3.9” barrel)… at least for me. The shorter barrel moves more freely in the slide, and the round can actually tilt the barrel as it feeds (actually, it straightens the barrel as it is already tilted up). The barrel on the full size model does not budge when the round hits the feed ramp. This difference puts an axially load on the cartridge, forcing it against the slide. The round in the full size does not get pushed against the slide, so the ejector claw fails to grab the rim of the case. This can all be seen by slowly hand cycling the slide with dummy rounds.
*
So, the RCBS boolit is good.

[GONRA]

Picky (PITA) GONRA sez - change "ejector claw" to "extractor claw".