Problem with new AR build

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tRidiot

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So my buddy and I built a new AR this weekend for his dad, and they took it out today to test it and get it dialed in.

Problem is, he said about 30 rounds in, it started getting lots of light strikes. He said probably 1 out of 3, then about 2 out of 3. He took the BCG out of his own rifle (which we also built and functions flawlessly) and it seemed to have a few less lightstrikes, but still having problems.

Ammo was plain ol' .223, not military 5.56 with hard primers, which was my first thought.

He took it all apart and soaked it with CLP, ran it super wet, no real improvement.

So...

I am sure cutting the hammer down would probably fix the problem, but I'm trying to figure out what the problem IS? I mean... if it were a problem with the firing pin or BCG, swapping in the other one from the alternate rifle should have fixed the problem. If it were a problem with the upper being gunked (most all of the parts have sat in my safe or closet for probably a year), cleaning it all out should have made a difference. He said the BCG was seating properly, using the forward assist made no difference. Mag was run through the other gun with normal function, no failures.

So the only thing I can think of is a weak hammer spring? I mean, cutting the hammer down should allow it to accelerate faster and strike harder, even with less mass. Sort of like you often have to do with the JP Low Power spring kit. But I've never really run into an underpowered hammer spring. I suppose we could have overtorque or stretched the hammer spring when applying it on the hammer, but... I dunno, that doesn't seem likely. It is applied properly with the more forceful direction of the legs pressing down on the trigger pin, not backwards like can result in walking of the trigger pin and malalignment of the FCG. I made a point to check this when we installed it.

I don't know, just looking for some ideas. I've been kind of wracking my brain since he called me earlier today to let me know about it.


<edit> Oh, components. Standard poverty pony lower, enclosed trigger guard. Same Anderson LPK. Generic buffer tube and spring, Bear Creek 16" nitrided barrel, mid-length gas, non-adjustable gas block, Primary Arms (I think) nitrided BCG, etc. I mean, I just can't see how anything other than the hammer or spring could have anything to do with this, can it? I'm no expert by any means, and failure to cycle, failure to eject, all those I could see being related to BCG, gas system, buffer system, etc. But not light strikes.
 

tRidiot

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I don't know, I'm gonna have him bring it back over in a little bit, the more I keep thinking about it, the more I think we HAVE to have put the hammer spring in backwards. I gotta pull it apart and check that first. There's just not many other possibilities.

I'll update when I know more.
 

swampratt

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Buddies Ar was doing that and we did the same as you did and no dice.
I built the same gun as his in fact I built 2 of them with the same parts and No issues.
I finally figured out the issue.

The shoulder Ogive on the brass was not set back far enough. Yes handloads.
My gun and the wife's gun run just fine never miss a lick.
Look really close at how far the bolt is going in .
Yes forward assist did not help even pounding it.
I ended up making cases for his chamber that have the shoulder set back .004" more than what my guns like.

Now I do have a bobbed hammer on mine and I also bent one leg on the hammer spring to remove a lot of tension and the other leg is tweaked some also that is my gun. and no light strikes ever I use hard cup primers CCI 450.

When I measured the firing pins on his vs mine his actually stuck out .003" more than mine.
So it was not the firing pin.
It was just case shoulder was bottoming out in the chamber before the bolt fully closed.

Know what sucks is a huge 10 point in front of you as you are laying on your belly in knee deep wet grass and the gun goes CLICK!.
Happened just like that and he chambered another and CLICK and another CLICK and then pounding and rechamber and deer decided to bolt.

SUCKKKKKK!
 

tRidiot

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Yeah, just talked to him on the phone, he can't bring it tonight, we'll check it this weekend. I talked him through it but I may not have been watching closely enough on the installation. I was letting him do the build, even pin and spring by himself, as it was for his father, I was just guiding him along and holding stuff here and there. I'm pretty sure that's gotta be it, I just didn't make certain.

We'll see in a coupla days.
 

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