AR15 bolt tightness/sticking question

[exo]

Has anyone had issues with a brand new bolt / BCG before? I don't know what to call it, but I think the "ridge" on the bolt is a little too high which may be the cause of my problem. Comparing by feel to my other, working bolt, there is a noticeable difference.

With the following setup:
Bolt A, Bolt carrier A
Bolt B, Bolt carrier B

Bolt A works in bolt carrier A and bolt carrier B.
Bolt B does not work in bolt carrier A nor bolt carrier B.

By "works" I mean that a quick function test ("flick") the bolt moves outwards nice and easy. By "does not work" I mean that I have to really flick the carrier hard to get the bolt to move outwards.

Using bolt B in any carrier results in a significant number of failure to fire, essentially making a single shot AR15. Probably 90% of all rounds fired in that configuration are problematic. It's not the ammo as when I switch bolts it works just fine, and all the ammo I was shooting is from the same lot.

Would you think I am correct in assuming that the "ridge" is the problem? Does anyone know what the spec dimensions would be? Is it worth trying to file it down?

Update, see post #13. Everything is working now, yay!

 

[WaldoOneFive]

I had a bolt that was too long on the small end where the firing pin goes in. It would prevent the firing pin from sticking out the bolt face enough to strike the primer, and thus I was getting light primer strikes. I had to file it down a HAIR to fix the problem.

 

[jasons]

Does it still stick if you remove the gas rings?

 

[1903Collector]

Maybe a picture if possible?

 

[Steve_P]

Are you running it wet with plenty of oil?

 

[andy t]

Who makes the problematic BCG?

 

[exo]

I had a bolt that was too long on the small end where the firing pin goes in. It would prevent the firing pin from sticking out the bolt face enough to strike the primer, and thus I was getting light primer strikes. I had to file it down a HAIR to fix the problem.

That's interesting, I'll try measuring there and comparing to my working bolt.

Does it still stick if you remove the gas rings?

I'll investigate that.

Maybe a picture if possible?

I'll take a picture of each bolt and post it tomorrow, I'm probably not going to be around tonight.

Are you running it wet with plenty of oil?

Yeah it's very wet.

Who makes the problematic BCG?

I'm not sure, it is supposedly milspec though.

Thanks for the replies folks, I've got a few things to look at and I'll report back.

 

[1903Collector]

I'm not sure, it is supposedly milspec though.

A lot of companies claim there stuff is milspec and it's not even close. Doesn't neccessarily mean it's bad just not milspec. A lesson I have learned.

 

[vellnueve]

Just as an aside... it's highly recommended that you don't switch bolts between rifles once they've been worn into that rifle. The Army manual specifically addresses it as well.

 

[exo]

Well, I measured that ridge on both bolts and they're the same, so I'd rule that out for now.

I had some brand new gas rings on hand, so I tried swapping them out on the bolt B (the misbehaving bolt). I swear the bolt is even tighter now. Is a break-in period typical for new rings?

 

[jasons]

Well, I measured that ridge on both bolts and they're the same, so I'd rule that out for now.

I had some brand new gas rings on hand, so I tried swapping them out on the bolt B (the misbehaving bolt). I swear the bolt is even tighter now. Is a break-in period typical for new rings?

Brand new rings can be pretty snug but they should never be THAT snug. (Certainly not to the point of causing malfunctions.)

Do they move freely? When you run your finger around them do they sink as far into the channel as your other bolt? (And evenly all the way around?) Maybe theres some "shmutz" left over from the machining process in there that's not letting the rings seat all the way?

Did you try the bolt in the carrier with no rings at all installed just to make sure it wasn't something else?

 

[andy t]

+1. Unless you the bolt was made by a reputable manufacturer, it's suspect.

A lot of companies claim there stuff is milspec and it's not even close. Doesn't neccessarily mean it's bad just not milspec. A lesson I have learned.

 

[exo]

Update: Everything is working properly now. Unfortunately I changed too many variables at once to really isolate the problem... I was much more concerned with getting a working rifle without having to go buy a new bolt.

What I changed:

• I worked the bolt back and forth by hand a bunch of times, that seemed to loosen it up
• I checked all my magazines for proper feeding. The ones that didn't work right I fixed (feed lip problem).
• While investigating the bolt I took off the gas rings and scrubbed the area underneath
• I was also having a problem with my trigger pin walking because the hammer spring legs weren't resting on the trigger pin like they're supposed to. I fixed that.

So for anyone else with a problem like this, my apologies as I can't pin it down to any one thing

Thanks for all the input, I'm just glad my rifle is working properly now