Feeding issue, narrowed down to bolt.

[JNG3]

I will not discuss the name of the manufacturer as I have not had a chance to contact them yet and I'm willing to rack this up as 'stuff happens'. Mostly curious as to what could be causing this.

Built my third ar15 last week. Went to test fire Saturday. Cartridge feeds from magazine into chamber but stops when cartridge is 2/3rds of the way into the chamber. I would have to drop magazine, pull charging handle fully to rear and let the bolt/carrier slam the cartridge into the chamber. 90% of the time this would work. 10% of the time I would have to pull charging handle to rear a second time. Does not matter if it's the first cartridge or the last from magazine. NHMTG and Magpul gen 2 mags were used. Chamber is 5.56, catridges were M193, headspace was checked prior to test firing using Clymer gauges. I suspected it was a bolt or carrier issue. After swapping bolts and carriers in my other two ar's, I determined that something is wrong with the bolt. I just don't know what. I ended up using a new bolt that I have on hand as a spare and the carbine ran fine on Sunday. The suspect bolt will not fully chamber a catridge in my other two ar's I own. I pulled the extractor thinking maybe the extractor was faulty and it still won't chamber a cartridge. The ejector moves smoothly so I doubt that's the issue. Any ideas? For the record, no fancy coatings or finishes, no low mass carriers or other high end parts. All basic mil spec type builds.

[26 Inf]

I will not discuss the name of the manufacturer as I have not had a chance to contact them yet and I'm willing to rack this up as 'stuff happens'. Mostly curious as to what could be causing this.

Built my third ar15 last week. Went to test fire Saturday. Cartridge feeds from magazine into chamber but stops when cartridge is 2/3rds of the way into the chamber. I would have to drop magazine, pull charging handle fully to rear and let the bolt/carrier slam the cartridge into the chamber. 90% of the time this would work. 10% of the time I would have to pull charging handle to rear a second time. Does not matter if it's the first cartridge or the last from magazine. NHMTG and Magpul gen 2 mags were used. Chamber is 5.56, catridges were M193, headspace was checked prior to test firing using Clymer gauges. I suspected it was a bolt or carrier issue. After swapping bolts and carriers in my other two ar's, I determined that something is wrong with the bolt. I just don't know what. I ended up using a new bolt that I have on hand as a spare and the carbine ran fine on Sunday. The suspect bolt will not fully chamber a catridge in my other two ar's I own. I pulled the extractor thinking maybe the extractor was faulty and it still won't chamber a cartridge. The ejector moves smoothly so I doubt that's the issue. Any ideas? For the record, no fancy coatings or finishes, no low mass carriers or other high end parts. All basic mil spec type builds.

The bolt lugs should have a very slight angle at the rear (on bolt guns they are camming angles) are they present? Measure the length of ALL the locking lugs on the bolt that works and the bolt that doesn't, any differences? Could be thoes areas are just a scoosh longer on the bolt that doesn't work.

[crosseyedshooter]

Is the new cartridge fully parallel to the chamber and seated in the bolt when it hangs up? Maybe the gas tube is
misaligned or there's something on the gas key that's rubbing on the gas tube.

If the cartridge doesn't slide into the bolt face and jams before becoming parallel to the chamber, then I had similar symptoms with a new BCG and it turned out the extractor spring and o-ring combo was too stiff for my buffer spring to overcome. Or there was a burr on the extractor hanging up the brass. However, you said yours still jams with extractor removed, which sounds like a different problem than what I had.

[JNG3]

The bolt lugs never get to the extention when it jams. The cartridge is not fully parallel to the chamber in the horizontal plane when it jams. Nor is the cartridge head fully inside the head of the bolt when it jams. I'm going to try pulling the ejector and see if that changes anything. The gas tube is aligned correctly. The problem goes away completely when I simply use any of the 3 other bolts I have. No other change is needed and that includes using the same carrier. All 4 bolts and carriers I have are from the same company. Like I said I'm sure it's either something silly I'm overlooking (like a small burr somewhere) or it's a case of I got a bad bolt. Stuff happens, no biggie.

[Iraqgunz]

Just to be clear, because your post is run together. Have you taken this bolt, put into another carrier or tried to put this BCG into another AR? If so, did it also create a feed issue? Sounds like there is an issue with the bolt lugs.

[TomMcC]

You could try firing 1 round without a mag installed. Does the bolt close and lock? If it does, maybe something on the bolt is dragging on the mag, slowing the whole thing down. If it doesn't close, reach in the ejection port and see if there is any movement in the bolt or carrier. If you get no movement, something is locking the whole works up as it strokes in the receiver.

Also, when manually racking the bolt with and without a loaded mag, does it feel normal?

[JNG3]

I have tried the suspect bcg and just the suspect bolt with a known good carrier (in order to rule out the suspect carrier) in my other two ar15's. The exact same problem occurs.

My two other ar15's have been flawless in operation until I tried the suspect bolt.

I had a brand new spare bolt on hand. I used it and the newly built ar15 functions perfectly. Yes, I checked headspace before firing the carbine.

It is only the bolt, not the carrier, that is the problem.

I understand the comments concerning the bolt lugs. However most of the time when the jam occurs the bolt has not reached the barrel extension yet.

[TomMcC]

I have tried the suspect bcg and just the suspect bolt with a known good carrier (in order to rule out the suspect carrier) in my other two ar15's. The exact same problem occurs.

My two other ar15's have been flawless in operation until I tried the suspect bolt.

I had a brand new spare bolt on hand. I used it and the newly built ar15 functions perfectly. Yes, I checked headspace before firing the carbine.

It is only the bolt, not the carrier, that is the problem.

I understand the comments concerning the bolt lugs. However most of the time when the jam occurs the bolt has not reached the barrel extension yet.

Then something is really wonkie about that bolt. Have you sat down at the old workbench and really compared it to a known good bolt. This is obviously a prob none of us have experienced. There has to be something really different from a good bolt.

[JNG3]

TomMcC

I can partially answer your question right now. Without a cartridge, the bcg closes correctly. And that is with or without a magazine. It is only when a cartridge is attempting to fully feed into the chamber does it jam. I have not noticed any dragging or extra effort needed to manipulate the bcg unless a cartridge is attempting to be feed.

[JNG3]

At workbench now. May have more info soon.

[JNG3]

PROBLEM SOLVED!

I pulled the ejector on the suspect bolt. Ran suspect bolt with known good carrier. Bcg strips cartridge from mag and chambers said cartridge fully into chamber and bolt locks securely into extention.

Pulled new pin, ejector, and spring from my spare parts collection and installed them. Tried suspect bolt again and had no problems. So either the spring was too stiff and/ejector is out of spec. Threw suspect roll pin, ejector, and spring in trash.

I refuse to hassle any manufacturer over a couple dollars worth of parts. Just glad it got figured out. Thanks to all who offered advise!

[MegademiC]

Thanks for sharing, very interesting.

[TacticalFun]

Glad you got it sorted

Sent from my SM-G920P using Tapatalk

[bamashooter]

Good deal.