I've been reloading for over 60 years, and never had a case separation incident until yesterday. I was fire-forming a bunch of brass for my 223 Wylde, using a very conservative load of Varget with a 65 grain Sierra as the projectile. CCI BR 4 primers and brand new Lapua 223 Match brass. Shot the first 11 loads with no problem, but in the 12th load, there was this strange "pop" followed by a failure to feed. I cleared everything, opened the AR, and saw an unfamiliar glint of brass in the chamber. I tried shaking it loose but it would not fall out, so I used a cleaning rod to clear it. As you can see from the pics, the separation cut on the case was very clean. Cannot figure out what happened. I hand-weighed each powder charge; the brass was new, with only one pass through an FL resizing die. Loaded the magazine and shot another 6-8 rounds of the same batch with no problems. I then tried a few other loads that I had with me and had no problems. Any ideas on what caused it? I'm thinking it just happened to be a bad piece of brass. Very strange. . .

What is the whitish horizontal line about half way between where the case tore and the annealing color change ends?

I don't know of anything to suspect other than a damaged or bad case from the get go.

It's a scratch that I believe came from having the separated case jammed into the chamber by the next round. The lighting (and poor photography) caused it to look white, rather than like scratch. I inspected other cases from rounds that fired successfully and there were no scratch marks on them.

How much are your cases growing at the shoulder from virgin brass to fired brass?

Chad, I measured 5 cases each of "virgin" and "fired" for length:
Unfired: 1.754 inches
Fired: 1.757 inches

Appears statistically insignificant to me. And as I mentioned, these loads were not at all heavy; I was merely wanting to fire form them so I was loading them on the conservative side of the Lyman recommendations for the bullet weight. I found no pressure indications on the cases of the remaining batch that I fired.

No, it's the shoulder for the head space measurement that would help determine how much the brass is stretching. The length you gave me is the case length. It's the head space measurement I'm asking for. This will determine if your brass is stretching too much during firing and causing the case head separation. The excessive stretch is generally what causes a separation on new brass. If it were reloaded and FL sized multiple times, I'd say the brass was at it's case life and done. But virgin brass tells me it's something else.

Here's a drawing showing the head space measurement and where you measure it from. You will need a case gauge or head space gauge to measure it.

Also, what is your load of Varget for this round with the 65 grain bullet?

Or a socket that "bumps" the shoulder...

I don't have a case gauge or head space guage, so I can't make that measurement, Chad. The load I was using was 23.5 grains of Varget. The case that separated was the last of the virgin pieces out of a bag of 100 pieces of Lapua brass that I bought about a year ago. So, I've used 85 of the pieces with nary a problem, in every loading from absolute minimum powder charge suggested to maximum safe load, and with every bullet weight and configuration that I've been able to buy. I keep track of the number of times I reload the brass, and am on my fifth reloading of 20 of the original 100; all the others have been reloaded fewer times. Would I not have had some sort of indication of head space problems show up before now? And for it to happen with only one case out of the bunch?

BTW, thanks to everyone who's made suggestions on the root cause of this failure!

I'm not sure then. The 23.5 grains is right at the minimum load. Without knowing the head space difference between virgin brass and fired brass, it's hard to know. But one case out of all of them is a little strange. Just throw it away, and keep going.

If you want to "redneck engineer" a head space gauge, find a 30 caliber piece of brass, like a 308 Win. Size the case or make sure it has a perfect round case mouth and the case head is flat with no burrs. You can insert the mouth of the 308 case over the mouth of the 223 case where the mouth of the 308 case sets on the shoulder of the 223 case. Then measure the length of that. You can compare the differences of the fired vs virgin brass that away. If you do it right and do measure multiple pieces, it will give you enough measurements to see what your head space growth is. (I've done this many times for headspacing on a 308 Win case with a 40 S&W case before I got the proper tools)

How far can you safely stretch a new annealed case in fire forming?

What is the difference in headspace between a 223 rem and 223 wylde?

Thanks, Chad; I'll try the .308 case trick, and then just for grins, I may take the whole package down to Apache Rifleworks next week and let their gunsmith take a look.

redchevy, I cannot answer either of those questions. I do know that the separation occurred further down the body of the case, well away from the annealed area.

I found this on the Pacific Tool and Guage site, written by Dave Kiff, the owner. Don't know if it helps shed any light!

We sell a gauge set for $99.00 that consists of a Min Go, +.005 No-Go and a +.010 Max SAAMI and Field gauge. Otherwise, you can purchase the SAAMI, CIP or Wildcat gauge in different lengths. We also grind an 11 piece gauge set in .001 increments that have a -0 to +.0002 tolerance. I have a lot of customers calling me about their hand guns or gas guns closing on the No-Go, such as an AR-15 closing on a standard No-Go gauge. Remember most gas gun manufacturers run their headspace a little longer for rapid firing and to have the ability to perform with a dirty chamber.
If a precision gunsmith chambers a bolt action barrel or an AR for you, he will most likely ream until the bolt just closes on the Go, but a +.005 No-Go should work as a No-Go. Remember, most manufacturers chamber their AR-15’s and other gas guns to +.002 for Go from SAAMI Min to +.007 from SAAMI Min for their production No-Go. I always check my gas guns with a military 11 piece incremental set of gauges to find out the true depths of the headspace. Example: A Min 223 Rem, 5.56 Nato, 223 Wylde or 20/223 practical Go gauge is 1.4636 to .330 shoulder datum. The 223 Rem No-Go is 1.4696 to .330 shoulder datum (for most bolt actions and precision chamber barrels). The military Max and SAAMI Max Field gauge is 1.4736 to .330 datum and some chamber their gas guns to the Max SAAMI Field of +0.10.

What is the difference in headspace between a 223 rem and 223 wylde?
None. The difference in in the throat.