I recently built a 6.5 Creedmoor and will post specifics once I iron out the best load and function. It is mostly JP and Aero precision. I have noticed others have gotten good accuracy out of 42.5 of h4350. I have found this to be a very accurate load as well but I am noticing hard ejection, extractor marks and now blowing primers. I did not notice pressure until I got to 42.5. I will admit that I am not very knowledgeable when it comes to adjustable gas blocks. It is a JP adjustable gas block but I haven't made any adjustments to it as of yet. It ejects cases at approximately 2 o'clock. Beating the hell out of my cases even with +2 gas system. These are new Hornady cases. 140 gr Hornady bthp. Also, using JP silent buffer. No evidence of pressure on factory Hornady rounds. Any advice other than the obvious of backing off on the powder? Maybe such as adjusting the gas? I really like the load regarding speed and accuracy but it's not safe the way it is.
Blowing primers on 6.5 cm JP build question
- Thread starter 10ring1
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My load with a 140 ELD-M is 42.3 of H4350. I also use a small base die. Mine is a factory rifle though. You should be ejecting closer to the 3-4 o'clock area. It seems like your gun is slightly over gassed. Reduce powder and tune the gas block to the new load.
I order to avoid beating/denting brass I used rubber bumpers on the brass deflector on the upper.
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I order to avoid beating/denting brass I used rubber bumpers on the brass deflector on the upper.
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You should turn your gas down and open it up one click at a time shooting shots in between till the bolt locks back. Now fire a 20rd string. If it feeds, ejects and locks back on last round your tuned.
Did you measure distance to loads? If so are you jammed or really close? Maybe back off the lands.. i had this very issue with rifle gas. After going +2 I haven't blown a primer yet.
Did you measure distance to loads? If so are you jammed or really close? Maybe back off the lands.. i had this very issue with rifle gas. After going +2 I haven't blown a primer yet.
Thanks for the input padom. Neglected to mention my coog is 2.255 which is max length I can get out of a pmag. When doing a seating depth test, the deeper I seated them the more primers blew. Attempted seating increments of 15 thousandths each time. Still getting blown primers.
I shoot this same exact load in my bolt and show no pressure signs at all.
I shoot this same exact load in my bolt and show no pressure signs at all.
Not at all. It's not the amount of pressure in the barrel causing the problem; it's the pressure operating the action. The higher pressure makes the rifle start unlocking the bolt before the pressure in the barrel drops. Turn the gas down until the rifle doesn't lock back on the last round. Then, load a single round into a magazine, load, and fire it. Open the gas block a little at a time, testing a single round each time, until the bolt locks back on the empty magazine every time.
Padom and Red are correct. The AGB will help tune the amount of gas working the action, you want enough gas for the system to work the action and it has to have enough gas to feed and eject reliably.
If you keep blowing primers and get swipes, reduce your handloads a couple of grains hopefully your accuracy node is maintained.
Can't really tell from the picture but are you getting flat primers too?
If you keep blowing primers and get swipes, reduce your handloads a couple of grains hopefully your accuracy node is maintained.
Can't really tell from the picture but are you getting flat primers too?
By any chance, you using a low mass bolt carrier group and/or light/std weight rifle length spring? Agree with all above about setting gas block. Are intact primers protruding at all from case head? Have three 6.5 CM AR's and run full mass carrier, Tubb flat spring, and SLR gb's in all with full reliability, but only run 41.5 H4350 with either 139 Scenar or 140 Amax. ASC Metal mags will let you run 2.835 with room to spare.
I was going to say, get some KAC or Larue mags that allow you to load out to 2.871". My 6 5cm 140 ELDM is loaded to 2.835 which is .02 off
I am running the JP LMOS bcg. And yes, out of about 10 rounds at that charge, 4 we're blown primers, 2 were protruding and 2 were intact and flattened. All had ejector swipes. Is the charge too high for the low mass bcg? I plan to adjust the gas next trip to the range
I have noticed the longer my coal, my groups continue to shrink. I have a few.metal.mags, DPMS, I think. I will have to try a longer coal once I get the gas straitened out.
Stronger recoil spring in conjunction with properly adjusted load and gas will get you there. KAC mags will let you go long, and are high quality, but pricey-certain. Have had excellent results with ASC at about 35-40% of cost of KAC's.
Yes, ASC. Pretty certain I picked up fm Midway. Tried to load pic, but with Scenar at 2.825", there is another.035 clearance, maybe a touch more.
If your blowing primers, you have way too much head space. I had the same problem with my gas gun, and no matter what i tired i was blowing primers.
It turned out that the bolt was the issue.
It turned out that the bolt was the issue.
JP barrels are available with a headspaced HP bolt-is that part of your build? If not, a set of go/no go gauges will answer that potential question. And if you're still good there, over sizing your brass? A Hornady headspace tool for your caliper will tell your how much shoulder setback you've achieved. .0025--.003 should be plenty for gas gun.
The over gas isn't going to cause your pressure problem but it will cause the gun to beat your brass up. The over pressure event is happening before the gas system is in operation and is a completely stand alone problem. Did it blow primers at lower charges? If not, reduce your load, just because it works in other peoples guns doesn't mean its good to go in yours. You may also try a touch slower burning powder to see if you get the same result. H4350 is probably going to give you the best velocity (especially in a gas gun) but it's worth trading some velocity for consistency and reliability if it's not working for you. As others have mentioned you should check headspace too and see if that could be causing your problem as well.
You should tune your gas system regardless though.
You should tune your gas system regardless though.
This... This was my initial thought with the pressure causing blown primers even before the gas cycle begins. I am going to try making changes Sunday. I am going to look for a lower node as well. No blown primers in lighter loads.
Yes. I am using the JP bolt which I was under the assumption that it was already headspaced.
Generally, I have found new brass to be much smaller in size than what your chamber is going to be. I don't think this is a headspace issue. Just do what red and others have suggested with your GB. I would also strongly favor running 42 or below grains of H4350. I know there are some gas guns that will run the 42.5, but this isn't the only time I have seen this. In fact, my LRP prefers a dialed-down load, so I run a 139gr Scenar with 41.7. Runs like a top and scary accurate too.
Finally had a chance to get it out today. Followed Padom's directions to a T. Amazing. I turned the gas off initially and started opening it each shot. It is very sensitive. As soon as it was reliable, 85 percent of the brass was falling in a nice pile at about 3-4oclock. About 15 percent going at 2oclock. The brass looks really good. Not one blown or flatened primer. The gum seems to run much smoother. Not as violent of an impulse. Very mild ejector swipe on about 50 percent of the brass but very mild.
I was under the presumption the load was over powered and the blown and flattened primers occurred even before the gas cycle occurs. That presumption was proven wrong. I am now leaning toward the primer may have been violently dislodged during the cycle
I was under the presumption the load was over powered and the blown and flattened primers occurred even before the gas cycle occurs. That presumption was proven wrong. I am now leaning toward the primer may have been violently dislodged during the cycle
