Gun is a Larue OBR 7.62 w/ 18" barrel. Cases are once fired military brass pulled off my range military range. Bumped the shoulders back and loaded to OAL of 2.80. Powder is RL-15. I went out today to do my ladder test. Start charge was 35.8g and final charge was 44.0g. Distance I did the test at was 200yds. Wx was light breeze, 60 deg, low humidity. The question I have is about the last 2 charges in the test. At 43.7g and 44.0g, the bolt did not lock back on the shot. It overran the follower on the back and pushed the follower back down so it was stuck about 1/2" nose down in the magazine. The mag was a PMAG that has a total off about 100rds through it. The cases did not show any signs off failure, and following the test we shot about 30rnds of factory FGMM in single shot and no problems with the magazines. I have not heard of this as being a sign of overpressure, but maybe it is. The problem is that those powder charges are in the most accurate node for the day, but its a show stopper if its overriding the follower.
Is this overpressure?
- Thread starter Munson
- Start date
Re: Is this overpressure?
You didnt mention the weight bullet, 168 maybe? 44grs will be too much, with military brass 42grs RE15 should be about right.
You didnt mention the weight bullet, 168 maybe? 44grs will be too much, with military brass 42grs RE15 should be about right.
Re: Is this overpressure?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: JGorski</div><div class="ubbcode-body">You didnt mention the weight bullet, 168 maybe? 44grs will be too much, with military brass 42grs RE15 should be about right. </div></div>
+1 44 is a bit hot in a gasser, my bolt likes 46, gas likes 42
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: JGorski</div><div class="ubbcode-body">You didnt mention the weight bullet, 168 maybe? 44grs will be too much, with military brass 42grs RE15 should be about right. </div></div>
+1 44 is a bit hot in a gasser, my bolt likes 46, gas likes 42
Re: Is this overpressure?
Sounds good to me. Like i said, i wasnt getting any overpressure signs from the cases, just the deal with the bolt not locking back after the last round. Thanks for the help gentleman
Sounds good to me. Like i said, i wasnt getting any overpressure signs from the cases, just the deal with the bolt not locking back after the last round. Thanks for the help gentleman
Re: Is this overpressure?
Munson,
I believe what you experienced is a sign of over-pressure.
I too shoot ARs in 308, and encountered the same phenomena you describe...in my case, I was doing load development with AR-Comp powder in LC brass. When i went 0.4gr above max, every primer was pierced, and the bolt failed to lock back on the last shot...that has never happened before.
It is odd though that your cases showed no visible signs of pressure...your primers ought to be flat, but more importantly, cases should have extractor/ejector marks.
You should post up the groups you shot for review, along with your cases. Since RL-15 is a temp sensitive powder, i would look for charges closer to 90% of max as a summer load, and 95-98% of max for a winter load...That said, i hate temp sensitive powders, and i'm willing to give up 50-100ft/s in order to have a consistent accuracy node and dope year round.
I disagree with the other two posters who make blanket statements such as "those charges are pretty hot for a gas gun". High pressure is High pressure, and it varies from rifle to rifle depending on the actual chamber dimensions and other factors.
I have two ARs in 308, and one is far more tolerable of hot loads than the other...as it turns out, my AR with a factory barrel is more tolerable of hot loads than my custom AR with a Bartlein barrel.
Best of Luck...
Munson,
I believe what you experienced is a sign of over-pressure.
I too shoot ARs in 308, and encountered the same phenomena you describe...in my case, I was doing load development with AR-Comp powder in LC brass. When i went 0.4gr above max, every primer was pierced, and the bolt failed to lock back on the last shot...that has never happened before.
It is odd though that your cases showed no visible signs of pressure...your primers ought to be flat, but more importantly, cases should have extractor/ejector marks.
You should post up the groups you shot for review, along with your cases. Since RL-15 is a temp sensitive powder, i would look for charges closer to 90% of max as a summer load, and 95-98% of max for a winter load...That said, i hate temp sensitive powders, and i'm willing to give up 50-100ft/s in order to have a consistent accuracy node and dope year round.
I disagree with the other two posters who make blanket statements such as "those charges are pretty hot for a gas gun". High pressure is High pressure, and it varies from rifle to rifle depending on the actual chamber dimensions and other factors.
I have two ARs in 308, and one is far more tolerable of hot loads than the other...as it turns out, my AR with a factory barrel is more tolerable of hot loads than my custom AR with a Bartlein barrel.
Best of Luck...
