AR only fires every other round

[sraiford]

Ok, here we go... My wife's friend brings me their AR that she bought at a gun show before the 1996 gun ban from a guy that built it. She bought it, never oiled it, never shot it, and has had it in a shed "hidden from her children" for 14 years. She brought it to me to clean and sight I'm for her. I cleaned it up, and the metal sucked up every bit of Hopps I put on it and it's still dry. I took it to the range and it only fires every other round at best. I've taken this thing down and compared it to my Bushmaster. Everything is in place, all the springs are installed correctly. I wicked my lower and upper with her's and this is what happened.

My upper and her lower worked perfect.
Her upper and my lower fired every other round at best

With this I figure it's her bolt assy. I tore it down, and it was bone dry.

What are yalls thoughts to fix the issue???

Thanks

 

[SGT_Kramer]

Is it a failure to fire failure to eject or failure to feed?

 

[kz45]

How about her whole rifle with your BCG

 

[hdfinder47]

Leave it alone - costs only half as much to shoot.

 

[Sesameball]

This ^^ (aggh, I meant to try your BCG in her upper).

Also, if it is not cycling properly (you were not clear on what the rifle was actually doing), check the gas block and tube. After 14 years there might be a dirt plug (eg. dirt dauber) or spider nest in there.

 

[sraiford]

I didnt try her rifle and my bolt, but will try that next. And it's a failure to fire, I do see light primer indents though.

 

[Crimson]

Clean the gas tube take the site block off and clean it really good, and check the gas rings on the bolt they may be lined up or wore out. It sounds to me your not getting enough gas to the bolt for it to completely chamber the second round. Try using the forward assist after every shot. I think its something with the gas if its not in the lower.

 

[sraiford]

When the rifle fires, it cycles as it should, but on the next trigger pull it clicks but no bang. I charge it and sometimes it fires and sometimes not.

 

[SGT_Kramer]

her upper may not be headspaced and you might be playing with fire. if you have alot of exesive headspace it can do exactly what your saying and may blow up in your face. Some guy put it together before youtube taught him how. Might be bad fireing pin also make sure take bolt completly apart and inspect thoughly.

 

[SGT_Kramer]

It's always a bad idea to go swaping BCG's without a headspace guage in hand. Once you see one blow up you'll never do it again.

 

[#1bambam]

Spiderwebs or beetles in the gas system from long term storage in a shed.

 

[Sesameball]

"It's always a bad idea to go swaping BCG's without a headspace guage in hand"

Crap. forgot about that.

Do you have a go/no go gauge*?
*disclaimer--I've swapped them (BCG/uppers in MY rifles which are assembled and headspaced properly) without problem--but, because the status of this upper(whether or not it was ever asssembled/headspaced correctly) is unknown, I'd gauge it first.

Good idea with the worn rings. They could also be lined up.

Anyway, now that we know you were getting weak/shallow strikes (ruling out bad LPK by prior swapping of the lower) and that the upper cycles properly:

Check that the firing pin is in good shape. I've heard of some that were blunted or "mushroomed" slightly, which can give inconsistent strikes. Good news: firing pins are cheap.

For interest, a discussion on headspace is given here: http://www.gunandgame.com/forums/general-military/38829-ar-15-barrels-self-headspacing.html

 

[Sin-ster]

My money is on headspace issues, and I'd recommend you don't put another round down the tube until you check it out.

There is of course also the possibility that the firing pin is warped, but that typically leads to consistent failures and not intermittent operation. That's where I'd look second.

You might also have some type of obstruction in the firing pin channel/bolt face, but a cursory visual inspection and thorough cleaning would address this. There's the outside chance that the bolt itself is out of spec in this regard. When you say you're getting light strikes, are they centered or closer to the outskirts of the primer?

The hammer might also be hanging up on the BCG somewhere, which could happen on two Lowers that were properly specced and assembled if the upper/BCG were to blame. Look for any new-ish shiny spots, chips, dings, etc. on both hammers, and the BCG itself. Also, does the charging handle move the BCG fluidly, or is there any extra tension/sticking/scraping?

 

[SirIsaacNewton]

When the rifle fires, it cycles as it should, but on the next trigger pull it clicks but no bang. I charge it and sometimes it fires and sometimes not.

If this is true it definitely has nothing to do with the gas system and I am almost positive you can rule out anything in the lower considering your upper and her lower worked flawlessly.

I think everyone who mentioned headspacing and/or firing pin issues is right on....

 

[headshot]

Leave it alone - costs only half as much to shoot.

LOL

 

[SGT_Kramer]

on a serious note I try and try to tell this to troops all the time. Never ever mix BCG this means everything from 240 B M249 and M16= AR 15 never swap bolt never try to trouble shoot yourself this way. A BCG may in fact headspace fine on same reciver and not another just like that BCG may headspace fine on another and not on that rifle. This is why we require every barrel taged on Crew serv and never a swap on personal weapons without aproval by DS GS maint. It may work fine or it may blow up in your face. I stress anyone that buys a built weapon from individual head space for own savety. I always do just to keep from having reciverver parts in my face forever and ever. Most parts made today are in spec but if you build a rifle with parts is't alot cheaper then plastic surgurey to buy a quality headspace guage!!!

 

[SGT_Kramer]

M2 50 cals will sometimes headspace fine on some guns and not others. It's fully adjustable on those but we still reuire tags to keep times quick and gun mounting fast.

 

[Sin-ster]

Bolt ≠ BCG

But sound advice for those without the technical understanding or proper tools to do it safely. Putting a used bolt into a different rifle can be VERY bad juju, and it's a good idea to check new items as well. Although if you stick to quality manufacturers, you're more likely to hit the lottery than find one that slipped through QC. In an emergency, I wouldn't hesitate to drop a new bolt into a rifle and go to town. But given even a few minutes with the gage, I'd definitely wanna check for simple peace of mind.

On a side note, it's possible to encounter problems with a BCG swap, but it takes a LOT of wear (i.e. rounds sent through the rifle). Don't try to rotate a single BCG through all of your rifles, and you'll be fine.

I can think of several dozen reasons (on top of these listed) why the military would not want parts mixed up, although I've heard from a few sources of the "solvent bucket" approach to soaking the BCG-- which never resulted in problems.

So how does this apply to the OP? I'd get a headspace gauge, find as many bolts as possible and give them all a shot (to headspace correctly; not at a live round). If the majority don't pass, whoever put together the troublesome rifle borked up on the barrel extension.

 

[sraiford]

I believe I found the issue. I can see two threads of where the barrel nut threads on. If so then I would say it is the headspace since the barrel is not completely seated.

 

[sraiford]

I have already fixed the rear sight because of shoty workmanship and now I see they installed the dust cover pin wrong. I don't have the tools to fix everything so I'll have to find someone in Mobile, Al to help.