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#3244603 - 05/17/20 11:35 AM Lr 308 platform blowing primers
varminter .223 Offline
Die Hard Member III

Registered: 03/01/10
Posts: 2685
Loc: south central Illinois
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?


Edited by varminter .223 (05/17/20 12:07 PM)

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#3244626 - 05/17/20 05:09 PM Re: Lr 308 platform blowing primers [Re: varminter .223]
spotstalkshoot Offline
Die Hard Member II

Registered: 12/22/13
Posts: 1801
Loc: so.mn
Web area not supported, brass expanding allowing pockets to loosen.

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#3244632 - 05/17/20 05:52 PM Re: Lr 308 platform blowing primers [Re: varminter .223]
varminter .223 Offline
Die Hard Member III

Registered: 03/01/10
Posts: 2685
Loc: south central Illinois
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.


Edited by varminter .223 (05/17/20 05:53 PM)

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#3244634 - 05/17/20 06:15 PM Re: Lr 308 platform blowing primers [Re: varminter .223]
varminter .223 Offline
Die Hard Member III

Registered: 03/01/10
Posts: 2685
Loc: south central Illinois
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.


Edited by varminter .223 (05/17/20 07:23 PM)

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#3244636 - 05/17/20 06:38 PM Re: Lr 308 platform blowing primers [Re: varminter .223]
arlaunch Offline
Seasoned Member

Registered: 04/09/17
Posts: 479
Loc: OR
V223,

What weight bullets are you shooting?

Do you know the distance to the lands on those?

What caliber is it you are shooting?
_________________________
Be consistent with your loading, practice your shooting, speak the truth, love your family and you will be rewarded.

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#3244638 - 05/17/20 06:45 PM Re: Lr 308 platform blowing primers [Re: varminter .223]
varminter .223 Offline
Die Hard Member III

Registered: 03/01/10
Posts: 2685
Loc: south central Illinois
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.


Edited by varminter .223 (05/17/20 07:03 PM)

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#3244642 - 05/17/20 07:08 PM Re: Lr 308 platform blowing primers [Re: varminter .223]
varminter .223 Offline
Die Hard Member III

Registered: 03/01/10
Posts: 2685
Loc: south central Illinois
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.


Edited by varminter .223 (05/17/20 07:11 PM)

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#3244643 - 05/17/20 07:28 PM Re: Lr 308 platform blowing primers [Re: varminter .223]
6724 Offline
Die Hard Member III

Registered: 01/19/11
Posts: 2908
Loc: colorado
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.

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#3244644 - 05/17/20 07:31 PM Re: Lr 308 platform blowing primers [Re: varminter .223]
varminter .223 Offline
Die Hard Member III

Registered: 03/01/10
Posts: 2685
Loc: south central Illinois
That my next step is to put an adjustable GB on it. I've got one on one of my ar15's. I just need to get up and swap it out.

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#3244661 - 05/17/20 09:31 PM Re: Lr 308 platform blowing primers [Re: varminter .223]
204 AR Offline
Die Hard Member with a vengeance

Registered: 01/31/10
Posts: 4910
Loc: Nebraska
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.
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#3244662 - 05/17/20 09:42 PM Re: Lr 308 platform blowing primers [Re: varminter .223]
varminter .223 Offline
Die Hard Member III

Registered: 03/01/10
Posts: 2685
Loc: south central Illinois
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.


Edited by varminter .223 (05/17/20 09:48 PM)

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#3244663 - 05/17/20 09:48 PM Re: Lr 308 platform blowing primers [Re: varminter .223]
spotstalkshoot Offline
Die Hard Member II

Registered: 12/22/13
Posts: 1801
Loc: so.mn
So you had an adjustable gb handy to try on a Sunday afternoon.

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#3244664 - 05/17/20 10:18 PM Re: Lr 308 platform blowing primers [Re: varminter .223]
varminter .223 Offline
Die Hard Member III

Registered: 03/01/10
Posts: 2685
Loc: south central Illinois
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.

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#3244706 - 05/18/20 03:47 PM Re: Lr 308 platform blowing primers [Re: varminter .223]
Plant.One Offline
Die Hard Member with a vengeance

Registered: 02/12/15
Posts: 4345
Loc: Oakland County, MI
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)
_________________________
All reloading info shared is based on my experiences in my guns. Follow safe reloading practice and work up loads from published minimum data.
This disclaimer will self destruct in 10 seconds.


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#3244755 - 05/19/20 09:25 AM Re: Lr 308 platform blowing primers [Re: varminter .223]
varminter .223 Offline
Die Hard Member III

Registered: 03/01/10
Posts: 2685
Loc: south central Illinois
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.

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