Monday, June 23, 2008

Warning: contents under too much pressure

Yesterday my brother Seth I got to do a little shooting to test out some new loads that I cranked out for my DPMS AP4. I had about 500 various prepped and primed .223 Remington cases that I wanted to fill with some bargain bin Remington 55 grain FMJ rounds that I had ordered from Cabela's. I consulted with my trusty Sierra V edition, 2nd printing reloading manual and my Lyman 48th edition manual to find out what would be a good all-around load for target or Armageddon.

The Sierra manual has loads that were tested on a Colt AR15A2 HBAR with 20" barrel and 1:7" twist. Looking at the 55 grain loads showed 23 grains at the low side and 26.1 grains at the high side with 3,100 fps expected from AA-2230. Works for me because I had a shiny new pound of AA-2230 sitting around for just such occasion.

The Lyman manual gave a different story, although I really didn't give it but a mandatory glance, and I should have paid more attention. The load for the 55 grain soft point was given with 25 grains of AA-2230 giving a velocity of 3,272 fps with a Colt AR15, 20" barrel, and 1:7" twist.

I wanted to load these rounds towards the hot side considering the chamber for this gun is cut for both the 5.56x45mm NATO cartridge which has more pressure, and the .223 Remington. I know, I know. I'm asking for trouble. The right thing to do is load several on the light side and then work up in powder charge until your either comfortable with the round or the ejected casings show signs of overpressure. I've been handloading for a long time, so I'm aware of the consequences, and also the rewards, of loading hot.

I went with 26 grains of AA-2230 and seated the round, after which I tried out my new Lee crimp die which gives a factory crimp. The die took about ten seconds to set up and delivered clean looking crimps on every round. I loaded 223 rounds (interesting) and then took off for my parents house for a little test and evaluation with my new Beta Chrony chronograph. I've never owned a chronograph before, and in my youth I tested my handloads by performance only. I took the reloading manual at its word, so I loaded what looked like a good performer and then checked for accuracy and pressure. It was that simple.

My goal was to shoot 23 of the rounds and then store the remaining 200 for the end of the world. My DPMS has a 16" barrel with a 1:9" twist rate, so I figured I would get about 2,800 fps out of it. I was wrong.

The first rounds clocked in at 3,278 and 3,250, and they sounded hotter than normal; like 5.56x45mm NATO judging from the muzzle blast. Looking at the first few cases (.223 and 5.56 cases - I know, I know) didn't reveal anything that would suggest that they might have too much pressure, so I let the barrel cool for awhile so I could shoot some groups. Accuracy was decent with one three shot group turning out at 7/8." Not too shabby.

Seth and I then set about shooting everything that we had on hand to find out what it was really doing. We quite literally had a blast. We fired a few different rifles: 7mm Magnums, .243 Winchester's, .22's, handguns. What a great time. Mother nature finally held out and decided not to rain on my day off, so that was a big plus.

At this point we fired off the rest of the loads for the DPMS, with Seth putting 9 rounds in the 8" Shoot-N-C targets at about 100 yards off hand, and some from a rest. Another look showed the resulting overpressure on the cases. I think the first rounds were Winchester cases which didn't seem to mind the pressure at all. The other cases were ones that I had picked up for months. Some of them were surplus, Federal, Lake City, Black Hills - you name it. The surplus cases had a crimped primer pocked which I reamed out to allow the primers to squeak by into the pocket, so it was no surprise to see that some of the primers were no longer in the case.

Other signs of over pressure were shiny or raised portions on the case head where the brass flowed into the ejector slot on the bolt face, and slightly deformed rims where the extractor had to pull hard to get he case out of the chamber. You can see this here in this picture. The case on the left is a Winchester which has been fired a few times. There's nothing wrong with it. The one in the middle is a no name case with the raised bump on the head at the 2 o'clock position, and the right case has the dent from the extractor.

I guess I'll lighten them up just a tad, and then finish loading the other 250 cases that I have sitting around.


Kevin said...

Word of advice: Don't reload Federal .223 brass. It's too soft, and has a nasty tendency to suffer case head separation, which can ruin your whole day.

Milsurp brass tends to weigh a bit more than commercial, meaning it's thicker and has slightly less volume, so it tends toward higher pressures for the same powder charge.

Bob said...

A.Using range pickup cases of unknown heritage is always a bit questionable, doubly questionable for hot loads, and triply questionably for SHTF ammo.

B. Did you only shoot 3-shot groups to test the load? I'd suggest a absolute minimum of a 5-shot group, and optimally a 10 or more shot group. A good discussion of the fallacy of shooting 3-shot groups is floating around at here:

Unknown said...

Thanks for the info. About half of the brass is from factory Federal ammo that I have been shooting for some time, and they appear to be the cases with the problems. I'm working on some softer loads, and I'll just use these for general plinking.

I was shooting off of a rickety table at my parent's house, so accuracy wasn't going to be on par. My brother and I did fire some 5-shot groups, but it was just too hard to keep the crosshairs on the target with the table wobbling back and forth.

I have some handloads that have turned out 5-shot 5/8" groups in this rifle, but they were fired from a solid bench.