AR not firing..

[kAnJii]

Hello all,
A friend of mine had trouble with his AR the other day at the range. The firing pin is hitting the bullet dead center but nothing is happening. His bcg won't close completely when releasing the bolt also. But when we swapped lowers, his rifle shot fine without any problems. But when I shot with his lower onto my upper, it wouldn't go off. I'm thinking a weak spring or need a heavier buffer. Am I correct, and if so, which would be the problem? Buffer or spring. Btw, he had a dirty bcg which he tore down and clean and lubed now. Would that make a difference?

[bigpig1]

Interesting, was it an 80% lower?

Sent from my SM-N900T using Tapatalk

[jeremyro]

Buffer tube might be dirty or your buffer spring might be weak. That could be causing the FTF. I would also try swapping out the hammer spring. They are cheap. Is it at factory built lower or a homebuilt one. It wouldn't be a 80% build would it?

[kAnJii]

Home built. I believe he upgraded the trigger to alg with yellow Jo springs?

[jeremyro]

hammer spring probably too light. What kind of ammo? The military 5.56 tends to have pretty hard primers

[The War Wagon]

Let's SEE what's going on.

[CK_32]

If you are seeing dimples on the primer your getting light primer strikes.

If you don't see anything your firing pin is not hitting.

To me it sounds like he probably put the hammer spring in backwards like most people do.

If he has the mil spec spring tell him put it back in. This is why you don't change/fix things that aren't broken.

Also what is "BCG not going all the way in" mean. Was there a 2mm gap? Or a 1" gap in the front of the dust cover. A small roughly few mm gap between the dust cover and from of the BCG is normal. The BCG is not the bolt. Usually the bolt is home when the BCG has a small window still to go.

If it's more of a 1" gap then yea that's not going into battery. And how many rounds is this rifle? New? Used? Always had issues? Issues just starting?

[kAnJii]

If you are seeing dimples on the primer your getting light primer strikes.

If you don't see anything your firing pin is not hitting.

To me it sounds like he probably put the hammer spring in backwards like most people do.

If he has the mil spec spring tell him put it back in. This is why you don't change/fix things that aren't broken.

Also what is "BCG not going all the way in" mean. Was there a 2mm gap? Or a 1" gap in the front of the dust cover. A small roughly few mm gap between the dust cover and from of the BCG is normal. The BCG is not the bolt. Usually the bolt is home when the BCG has a small window still to go.

If it's more of a 1" gap then yea that's not going into battery. And how many rounds is this rifle? New? Used? Always had issues? Issues just starting?

Yes, dimples on the primer.
Like you mentioned, about 1-2mm space from being completely closed.
Thank you for these extra questions..I'll have him replace or see if the hammer spring is inserted correctly.the rifle does fire, but out of 5 shots, he may be 1-2 in.

[Kmai24]

Lighter springs, lighter strikes. Try switching back to stock springs to see. There's a lot reviews on JB yellows springs and certain primers(sorry forget which ones were the hard primers). I have yellow springs one of my builds and reloading using Remington spp with no issues.

[CWM4A1]

Very likely the hammer spring is installed backwards. I see that very often on home built AR. See below link for correct hammer spring position.

http://oi43.tinypic.com/2hd1kqb.jpg

[baih777]

Home built. I believe he upgraded the trigger to alg with yellow Jo springs?

I run this in my 3 of my AR. mine works great.
if its a 80% lower its not machined correctly.

[baih777]

Very likely the hammer spring is installed backwards. I see that very often on home built AR. See below link for correct hammer spring position.

http://oi43.tinypic.com/2hd1kqb.jpg

^^^^^^this too

[AceGirlsHusband]

Makes me wonder if the bolt is going all the way into battery. Have you checked the headspace with go and no-go gauges?

[CK_32]

Yes, dimples on the primer.
Like you mentioned, about 1-2mm space from being completely closed.
Thank you for these extra questions..I'll have him replace or see if the hammer spring is inserted correctly.the rifle does fire, but out of 5 shots, he may be 1-2 in.

Yea sounds like a light primer strike issue. Simple fix. Install the factory spring correctly just to be sure.

Then if he wants, retry the yellow spring. Problem should be solved after that.

[kAnJii]

Thx guys. Great advice.