Not short stroking now, but groups suck!

[hogwylde]

Now that I have over 1000 rounds through my DEF-10, it runs like a top.  No short stroking or FF or any other "function" problems.  Now..........it seems like I can't hit the side of a barn.  Took it out for a 3-gun match.  Thought I had it zeroed a while back, found I was hitting high and to the right (200 yds, 12in high, 4in right when I went back to the range and checked the zero).  Walked my group down where I wanted it and went to a match the next day.  Now, I'm shooting 12 inches low!  I remember one of my 5 shot groups looked like a 6 inch vertical string, and all my groups (@ 200 yds) are about 6 inches at best.  I'm using 147g ball ammo.  I get the same thing with 168 match ammo.  Groups that are 6+ inches and no consistency.  I'm thinking this thing should shoot better groups and not vary day to day where is hits.

I did have a primer failure a while back when breaking this thing in.  Blew the bottom and guts out of my magazine.  Stopped shooting, inspected everything for bulging/obstructed bore/anything unusual....found nothing.  I've had no problems with function of this rifle now, but I'm concerned that maybe the barrel might be loose or the upper cracked or something allowing the barrel to wiggle around relative to the scope?  Anything I should check that I haven't already mentioned? 

Edited October 27, 2016 by hogwylde
modification

[jtallen83]

Headspace? Scope mounts?

[blue109]

Blowing the guts out of a magazine seems like more than a minor failure...details on that?

[Robocop1051]

I've never had a primer failure due that much damage. I was present when a blown casing did that, but that blew the action and receiver apart too. 

 

[planeflyer21]

On the little brother ARs, blowing out the magazine is a symptom of casehead failure, correct? (why you don't use the magazine/magwell for a foregrip)

Were you able to check all your brass?

[survivalshop]

    Not enough info . Need to know what type ammo was used to cause this failure , very dangerous condition . 

   Has the Head space been checked on this rifle , as said above . Also it will take more then a Primer blown out top cause a Magazine to blow apart . Was the Cartridge case saved & what condition was it in , any photo's ?

 Chamber not to spec's , loose Barrel , Muzzle device issue , as said, loose scope or mount . 

Start with Head Space check & Chamber inspection , see if Barrel is loose . That blow out is kinda scary !

[Sisco]

If you can't figure it out, definitely use that Armalite Lifetime warranty. Send it back and have them go over it. Include the magazine when you do.

[hogwylde]

The ammo in question was some MILSURP 308 ammo I inherited.  Cases were stamped TZ 79, TZ80, TZ81.  I've since learned that this is surplus Israeli ammo that is prone to case failure.  Inspection of the cases from that shooting session showed multiple case "ruptures" and one with the entire primer face missing.  I'm not sure which particular case caused the steel DPMS style magazine to dump it's guts.  It bent the base plate and "ejected" the mag spring/follower/remaining rounds onto the bench.  Straightened the base plate, re-assembled the magazine and it (the magazine) functions fine.  I've since junked all that crap ammo and have been using PMC Bronze and ATI for range sessions.  NO indications of case bulging or any other abnormalities with the brass. I haven't had the opportunity to check anything on gun since the last range trip with the groups all over the place.  I'm curious about the no name muzzle brake I installed right after I got this thing.  I want to re-install the factory flash hider and see if things get better............

 

[mrraley]

something that hasn't been mentioned yet....

 

What bbl are you using?

What twist is bbl?

What weight of bullets? (I see you mentioned 147 and 168)