Issues with Steel Case 7.62x39 AR

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I had several rounds yesterday not go off in my newly build 7,62x39 AR.

AR-Stoner upper with standard parts kit in a lower. Had 5 rounds not go off out of 30 today. Looks like it is getting good contact with the primers. Rifle worked well other than a few rounds not going boom.

Thoughts?
Upgrade hammer spring which one to buy?
Should I just chalk up to crap ammo?

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Don't have any brass ammo in 7.62x39. 25 rounds did go bang out of the mag only 5 didn't. Tried to recycle two of them and still no go.
 
Russian ammo has very hard primers meant for full auto LMG fire. Mini 30s will do the same thing with steel cased ammo. Unfortunately, you need an AK or SKS to really have good reliability in most cases with com block ammo.
 
I agree with Nodak- first, try an enhanced firing pin, and then an extra power hammer spring.

You mentioned "standard LPK" up there. Is the hammer the larger full mass ones, or one of the lighter and smaller hammers? You can tell by google image searching which is which. If it's a smaller speed style hammer, it may be lacking mass for proper whackage on the firing pin.
 
For the most part to get sure fire on steel case Russian ammo you'll have a compromise of decent trigger pull and sure fire when pulling the trigger. A heavy hammer spring will help, but you'll end up with a heavier trigger pull. If it were me I'd get one of the nickle coated trigger sets from Right To Bear and a standard weight spring set. Then add the 7.62x39 enhanced firing pin. The RTB trigger is cheap but pretty nice compared to milspec. If that doesn't help go to the heavy spring set. I did this on the few 7.62x39 uppers I have and I have no more issues with any ammo.
 
Found an enhanced firing pin and spring. Will try the pin first to see if that helps. Thank You.
 
I have the same ARStoner upper from MidwayUSA. I have only shot 1966 dated, steel cased, communist surplus ammo in it so far and it always fires just fine. In the next week I will try firing Golden Tiger steel in it.
I have a BearCreek Arsenal upper in 7.62x39 and it eats the Golden Tiger steel with no problems too.
What brand of steel ammo are you having the problem with?
 
If the primer strikes on the rounds that did not fire are the same as those on the ones that did (location, depth, etc) then I would blame the ammo, not the gun.

Do get some brass ammo as a control group, at least. Powering up the firing pin strike for the combloc ammo might be needed, but you don't want to take it to the point it pierces primers on other stuff.
 
Check to make sure your AR is going into battery all the way. Light strikes like shown are often indicative of not going into battery. Probably ammo-related (dimensions).
 
Fairly common issue with the X39 AR (AR47?) Midway even mentions (or at least used to) that it is common to have trouble with steel case mil-spec ammo. I 'enhanced' my own, it wasn't a spring issue but the firing pin needed to be able to reach just a tiny bit deeper. That said I would also not use anything but a standard hammer spring either, but its been 100% for a few thousand rounds of Wolf/Tula/Red Army fodder since the modification.
 
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