Rifle is in .223AI. Had approximately 800-900 rounds on it when it started having problems. ARC CDG action. Barrel was chambered by a local smith who does great work, and he used a known good reamer.
Beginning around the 900 round mark, I've starting getting the occasional round that appears to be WAY over pressure. It's deforming the unsupported part of the case and popping the primers. The case is so deformed I have to really work at it to get the bolt back. I've checked everything I can think of that might be a potential cause.
Started with virgin Lapua .223 brass. Fireformed 300 pieces, then started load development.
All bullets (88 ELDM's) from the same box of 3,500
All powder from the same 8# jug of Shooters World Precision (varget copy)
CCI 450 SRM primers, all from two boxes
The barrel has been speeding up steadily since completion of load development. My original load of 24.1 g has sped up almost 200fps in 700 rounds. Accuracy has always been good, shooting into 1/2" consistently. SD's weren't great, but acceptable for my purposes in the high teens.
I had my first popped primer with that original load. Primers were starting to get a little flat, but I didn't think too much of it. I dropped the charge back to 23.2g to get back to my original velocity. It has continued to pop primers, roughly 1 in every 25 shots. The other 24 of 25 fired cases look perfect.
I've checked everything I can think to check:
Powder is being thrown by an auto trickler. I accept charges that are right on or one kernel low. If it's a kernel high, I re-throw. The scale gets recalibrated regularly and has shown no signs of drift.
I measured about 200 bullets for diameter with a micrometer, weight, and base to ogive. No anomalies detected.
Seating depth is consistent to about plus/minus 0.002" Bullets were 0.030" off the lands when I did the original load development. I haven't check for throat erosion, but I'm sure the lands are farther away now.
I've scrubbed the bore and cleaned thoroughly for carbon several times. The borescope shows firecracking where you would expect, but no carbon build-up.
Here's my loading process:
Deprime
Clean the brass in SS pins
Anneal on the AMP annealer
Neck sized for the first two cycles on the brass, went to full length sizing on the 3rd cycle (the one I'm on now)
Charge with powder and seat the bullet.
The switch to full length sizing MIGHT correspond to the start of the problem. I don't track round count well enough know for sure. I'm bumping the shoulder back only 0.001" when full length sizing.
I'm at wits end. Out of desperation I loaded up 15 rounds with Varget, same 23.2 charge and shot them Saturday. Velocity was within 10fps of the Shooter's World Precision load. Slightly less pressure though as the edges of the primers were "rounder", if that's a word. No popped primers. I dunno what else to check and am hoping someone here has a great idea.
