Pressure signs - JRC 40S&W

[Forgetful]

The other night I crafted a block for holding brass for cutting the primer pockets to Large Rifle Primer width and depth. Made it nice and snug, using a 1/4" punch to push cases out from the bottom after cutting. So I deprimed the first case, and cut the pocket, and as I was putting it in the tray I realized all of these cases are showing signs of overpressure. I think. I never looked for it before because I always used factory loads in this. Here's a photo, and the first case has the large primer pocket I just cut. It also has it's flash hole uniformed for large rifle brass. (explanation and reasoning is in another thread)

Do I have a pressure problem, or is this just a result of soft small pistol primers? Some are cratered, some are cratered so badly that the divot is swelled out of the primer. They don't seem to be flattening but I didn't compare with a loupe or anything.

[Pinsnscrews]

edited-found your other thread.

I would measure the headspace. It might be loose enough to be causing the primers room to flow. I would also measure the case head, .40SW tends to bulge at the head in unsupported chambers, or loose supported chambers. Redding makes an exceptional die to remove the Bulge. I use one for my 10mm loads.

[Forgetful]

Cases aren't bulged or marred. This semi-auto tends to chew them when it spits them out, these were the once-fired that weren't mangled.

They were all AE 180gr FMJ-TC.

[tazman]

My 40S&W Taurus leaves primers looking like that with everything. New factory and reloads alike. Light loads and heavy loads both. I think the hole around the firing pin is slightly too big and leaving a cratered look to the primer. If you notice, the edge of the primer is still nicely rounded. This suggests there was no over pressure.
The primers are not punctured so I wouldn't worry about it any further.

[Forgetful]

I think the hole around the firing pin is slightly too big and leaving a cratered look to the primer.

It does look like it flowed into the firing pin hole, sometimes pushing back the firing pin itself.

I'll make some cat sneeze loads using the LRP's and see how the JRC likes them before I get too deep, and before I cut 1000 brass for LRP's.. 25 should be enough to start testing with.

[popper]

FP hole for the 'blaster' is probably designed large so it doesn't stick when dirty. Design changed the buffer & spring? Not ready for prime time yet.

[243winxb]

The JR Carbine is a direct-blowback design. http://www.justrightcarbines.com/FAQs.html Poor choice for a 35,000 PSI + cartridge. IMO.

The bolt is entirely inertial and does not lock when in battery, and the barrel breech does not depress upon firing, so there is no mechanical action to absorb some of the recoil energy as there is in the 1911 or Glock, for example.

Note that the 10mm at 37,500 PSI can not be made to work in the JRC. Not good if handloading 40 S&W ammo for it, without pressure testing equipment.

[brown bass hunter]

I have one of the JRC's in 40 and have been shooting an upper end load of Titegroup with Lee 180TC cast boolit and have not experienced any issues of yet. I just started using my M &P 40 load and it cycles perfect and is fairly accurate in the little carbine. Look forward to seeing updates on your progress on the LPP in your brass.

[Forgetful]

Note that the 10mm at 37,500 PSI can not be made to work in the JRC. Not good if handloading 40 S&W ammo for it, without pressure testing equipment.

They couldn't get a heavy enough buffer to get enough value out of the 10mm.

[Wise Owl]

See if the end of the hole at the place the firing pin exits
has a small radius. ( chanfer )

[fcvan]

I have 2, 9mm carbines (AR, Marlin Camp 9) and of course, both are blow-back. I was thinking of building up a locked breach 40 S&W. I figured it would require a pistol length gas system, probably piston driven with an adjustable gas block. Then I got to thinking that a .357 SIG would be a fun try as well. After much consideration I started adding up the projected costs of the endeavor. Yes, I still want to do it but the 9mm AR shoots my standard loads (125 PCd over 5 grains of Unique) so darned well, why bother? Sure, a heavier slug like the 40 would have quite the whollop and the .357 would have more case capacity with the same 125 boolit and likely much greater velocity. The 9mm through a 16" barrel is scooting right along at about 1550 fps. That is plenty enough to put the hurt on tin cans.