Lr 308 platform blowing primers

varminter .223

Active member
Reasons an auto loader will blow out a primer?
Excessive head space? How much?
Over pressure?
Lube in chamber causing pressure?
I'm not convinced lack of friction on case walls will cause a blown "out of pocket" primer.
Likewise too smooth of a chamber?
I believe cratering is from firing pin hole slop.
Chronographs right on with published load date figuring 30 fps per inch loss.
This barrel has a reputation for blowing primers and it seem to show up for me after applying a liberal dose of wd40 to the bcg chasing a cycling issue which ended up being the stoner mags. The rear of the follower sticks down no pushing case head up against feed lips. Magpul works flawlessly.
Biggest issue was with some hand loads for my axis that has a shorter head space with shoulder bumped back more.....about .009" shorter that a fired case.
Both of my bca barrels ran this same dogtown lot great. Previous own had issues as well but with a suppressor.

One other thought....excessive gas?
 
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I prepped all the brass that had been fired through that chamber and all pockets seem to be tight. I threw the ones that blew the primers away so they didnt get measured but over pressure with swell cases there as well.
I chronographed 2 dogtown rounds this morning and while the crater was there the primers still had a round edge and no major swipes.
 
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Did a bit more measuring and the area just forward of the extraction groove seem to be out of round by .001" or a bit more
New case .4665
Case fired in bca barrel .4695ish
Case fired in this barrel .471ish and out of round .001" to .00125"
Resized case .4685 to .471, Case with less head damage apparently are the small once since the die doesnt go down that far.
Cases fired through savage axis .469ish.
The ish is due to a 15$ caliper that reads .0005s.
The hand loads that blew primers the worst had huge swipes as well. I dont think the dogtown had much swipe just blew one primer and had some horrid cratering which could all be due to a big firing pin channel.
They chrono 3430 ish in this 20" barrel.
Original owner chronographed them at 3395 over his magneto speed. These speeds dont suggest over pressure imo.
Out of round brass and an extra .002s growth concerns me.
I also wonder if bolt timing could cause blow primers. Obviously big swipes means pressure is up and or bolt thrust is high and the bolt is unlocking. GB is non adjustable and barrel has been run suppressed for maybe 350 rounds of fairly hot dogtown ammo.
Resized cases that measure .470 still have nice tight primer pockers.
 
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V223,

What weight bullets are you shooting?

Do you know the distance to the lands on those?

What caliber is it you are shooting?
 
It chambered in 243 winchester and 70 varmageddon are what the dogtown are. Hand loads are 70 ballistic tip. I reduced them to 39 grains of varget and ended up with an accurate load at 38.7 and 2.690 oal which also seats a 70 varmageddon at the same 2.680 that the dog towns are. Its only 6x6.8 speed though at 3280 so that's not gonna work.

I have not measured to the lands.
 
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I should also add the primer blowing load was 55 bt and 44 h4895 at 2.650 that is what shoots in my Savage.
Being that's a different powder I'm not sure if that could significantly affect bolt timing with the 55s versus the 70s in the dogtown which looks like imr 4895 to me.
 
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My ar10 in 308 did that a lot. Armalite said there was nothing wrong with it. It sat for years as it destroyed brass. I finally modified the gas block to reduce the gas, works fine now.
 
Sounds like too much gas, at least that's where I'd start. Suppressors definitely multiply the problem, but since you don't run one you should be able to get this sorted out a little easier.

I struggle with getting good speed out of a 243, it just seems like it's a round that shows pressure before it should. I fought with my G2 243 all day today, never did get a consistent load under moa at 200 yards.

So yeah I'd start with the adjustable gb and see where that gets you.
 
The adjustable gas block seems to reduced swiping by half or better, eliminates blown primers and cleaned up most of the swiping. Very light ejector mark with gas off and some primers are fairly flat and some with a nice round edge. I have pulled a few of these dogtown loads and they are off by quite a bit though. Case heads with gas off look pretty much like the rounds with my final 2.25 rounds open.
My best guess is that it was already running on the ragged edge of too much gas and after I had sprayed WD-40 on the BCG it might have dripped on the next round in the mag and got into the chamber causing a slick chamber wall and heavy bolt thrust.
 
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I had one Joe Bob's that I had put on a 6x45 just because that's what I had at the time. Needless to say it wears a non adjustable now. I have no idea what I would do without a 100 yards range in my front yard. I would have a lot of unfinished projects that is for sure.
 
please tell us more about the load you're having trouble with and your load developement procedure you're following.

please provide as much info as possible, including but not limited to

Powder (and how much)
primer
bullet
brass
OAL
crimp info (if any)


without that information a lot of what we're doing is playing W.A.G..... (wild @$$ guess)
 
Issue was resolved with the adjustable gas block... atleast so far.
Only loads I tried were factory 70 grain dogtown from midway besides the 55 grain 44 h4895 load I had developed for my savage bolt gun. Primers are cci 200 and RP brass in that load.
I did find an accurate load when reduce to 38.7 grain of varget with 70 bt's and cci 200s in dogtown brass at 2.680.
It was slow as heck but still had cratering and primers flat with a round corner. The chronograph tells the tale that my problem is not excessive pressure though because all of the velocities are right online with load data If I subtract 30 ft per second per inch barrel since it is a 20 inch tube.
I think all of this information was in a previous post.
 
Original barrel owner also shot 70 grain Dogtown through it and the first 300 were fine. When ordered more the 2nd lot was blowing primers he sent them in the Nosler and they told him they had some that had excessive headspace. He also found online where other people were having the same problem. The two lots of ammo that I had had no issues whatsoever in multiple Bear Creek Arsenal 243 barrels.

Once again it looks like my problem was excessive gas speeding up the bolt unlocking and I think a little WD-40 must have been drugged into the chamber because the problem became more pronounced at that point. I had sprayed some on the BCG trying to figure out what I thought was a short cycling issue which turned out to be bad magazines which were stoners. The rear of the follower and the rear of the cartridge where hanging down in the mag so the lugs wouldn't catch it and it would slip by. I switch to a PMAG and the problem disappeared.
We often put a little shot of WD-40 on a AR-15 bolts and never had an issue but apparently this platform doesn't like that.
 
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Got the rifle back out the other day to check for poi on the first cold barrel shot after sitting for a while and it was back to blowing 3 out of 10 primers. Pulled the barrel and will be contacting the manufacturer. Cases are growing .004" to .006" just forward of the extractor groove even with gas shut off.
 
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Look into a high pressure bolt. JP sells them, but they can be pricey. A cheaper option is Aero Precision. Any of their non NiB bolts and carriers are high pressure.
 
But what doesn't make sense is that I have had 2 different BCA 29" 8 twist .243 barrels on this upper shooting the same ammo with zero issues. My other BCA upper shoots this ammo fine as well.
 
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