Wednesday, April 27, 2016

Sorting out the P250, Part I...

So I took the P250 to MCF&G yesterday morning and ran some chronograph tests.

The Armscor was not as weak as I would have supposed..
Armscor .380ACP 95gr FMJ
LO: 881.7
HI: 950.4
AV: 919.7
ES: 68.75
SD: 21.16
That's actually fairly warm for .380 FMJ range ammo. Thinking back carefully to those few strings of fire in Topeka, did I actually have any failures to eject? Or were they all failures to feed? Was I just superimposing memories of the Canik test and automatically assuming underpowered ammo was the culprit?

I have to say that I honestly do not remember any failures to eject. They were all failures to feed, and of a very specific kind, to boot.

See the picture above? Notice that the extractor claw is not popped fully out of the frame?

In a tilting-barrel recoil-operated gun, the slide moves forward and pushes the top round in the magazine forward. The nose of the bullet bumps into the angled feed ramp, which points the nose of the cartridge up and toward the chamber. At some point in its forward travel, the cartridge is freed from the feed lips of the magazine and the rear of the cartridge slides up the breechface, allowing the cartridge rim to slip under the extractor claw and the slide to close on the chambered round.

(I warned you that this was going to get nerdy and to tape up your glasses, didn't I?)

The first part of the travel is pretty easy. It's almost comical the way most folks have a knee-jerk reaction to "Polish the feed ramp!" as though this were the cure for every feeding ill. A polished feed ramp is pretty but doesn't have a ton to do with feed reliability. All the feed ramp needs to do is bump the cartridge in the right direction.

What is happening here is that the cartridge has made it around the "first corner", in that the nose of the round has been bumped into the correct upward orientation by the feed ramp, but it hasn't made it around the "second corner": The rear of the cartridge has not slid smoothly up the breech face and under the extractor claw.

The Armscor round is on the right, and a round of CCI Blazer Brass FMJ is on the left. Note that the Armscor round is a tiny bit longer, has a much pointier ogive to the bullet, and the rim appears to be a smidge thicker, too.

This pistol has been stone cold reliable over the course of 2,000+ rounds with everything fed it except the Armscor. The solution is obvious:
Patient: "Doctor, it hurts when I do this."
Doctor: "Then stop doing that."
While I was at the range, I also ran a chronograph test on Speer's 90gr Gold Dot hollowpoint load for the .380ACP. To say I was surprised by the results would be an understatement...
Speer .380ACP 90gr GDHP
LO: 1052
HI: 1099
AV: 1080
ES: 47.80
SD: 14.45
That's smokin' hot for major label .380 ammo. That's 160fps faster than Hornady Critical Defense and 240fps faster than Barnes TAC-XPD fired from the same pistol. I hope to do some ballistic gel testing on this load soon.