AR Bolt Won't Lock Back

[Ninsho]

The past few times to the range, the bolt on my NES build doesn't want to lock back. The issue seems to be intermittent, and didn't exist the first time I took the rifle to the range.

Any AR15 experts want to clue me in on the possible causes for this so I can solve this problem?

Thanks!

 

[doobie]

Have you tried different magazines? Could be a bad mag.

 

[hminsky]

Maybe the magazine isn't quite locked tightly? It probably wouldn't feed in that case, but it might just be on the edge or something.

 

[1903Collector]

Did you change ammo perhaps? Does it happen with different mags or just one?

 

[Cross-X]

Try changing the mag springs

 

[BillO]

Download this. It addreses the problem, page 52. Hope it helps.

http://www.ar15.com/content/manuals/manual_bushmaster.pdf

 

[Ninsho]

Did you change ammo perhaps? Does it happen with different mags or just one?

Same ammo the whole way through.

 

[Ninsho]

Have you tried different magazines? Could be a bad mag.

It happens on several different mags.. and sometimes doesn't on the same mags.

 

[Ninsho]

Download this. It addreses the problem, page 52. Hope it helps.

http://www.ar15.com/content/manuals/manual_bushmaster.pdf

Thanks, looks like it could be the magazines or the bolt catch from this. Guess thats fairly intuitive. I wonder if there is a good way to check and ensure this is or isn't the mags... before I go and replace all of the springs and followers for all my mags...

 

[Ninsho]

Oh, just remembered, another potentially useful piece of info: after my first time to the range I noticed that my a2 stock seemed a little shaky so I loosened the screw, pushed the stock back in tighter, and put the screw back in. Could this be related to my problem?

 

[JohnFH]

My Hbar did the same thing when it was new, the bolt catch was sticking a little.

A little oil and working it by hand and loosening it up a little fixed it. 1000 rnds plus since with no issues.

 

[vellnueve]

I'd concur with JohnFH. It could very well be a sticky bolt catch. Manually operate it until it's loose.

 

[Ninsho]

I cleaned then re greased and worked the bolt catch Saturday and shot it this morning, no such luck.

It did still feel a little gritty, so maybe it just needs a little more working before it functions as I would like. Could my re tightening of the stock done it? If it impacted the travel of the buffer at all couldn't it give me problems with the bolt moving far enough back to catch?

 

[Kaos116]

Just throwing this out there. Is the proper spring in the bolt catch assy? Possible mix up between the disconnector spring and bolt catch spring?

 

[vellnueve]

I cleaned then re greased and worked the bolt catch Saturday and shot it this morning, no such luck.

It did still feel a little gritty, so maybe it just needs a little more working before it functions as I would like. Could my re tightening of the stock done it? If it impacted the travel of the buffer at all couldn't it give me problems with the bolt moving far enough back to catch?

Doubt it, if it's an A2 stock. If it were an A1 stock and you were using an A2 screw, then possibly.

I don't know how comfortable you feel doing this, but knocking it out and cleaning/polishing the contact surfaces and the recess may be your best bet.

 

[1903Collector]

I had the same probelm with my 6.8 upper, ended up being a loose carrier key. Had to remove it, clean, reinstall and restake the screws. I think that is a rare occcurance but ya never know.

 

[vellnueve]

With the upper removed, does your bolt catch move back and forth freely?

 

[Ninsho]

Just throwing this out there. Is the proper spring in the bolt catch assy? Possible mix up between the disconnector spring and bolt catch spring?

Thats an interesting theory, I did have issues with my disconnecter spring during assembly, it was already in the well with the trigger. Perhaps whoever collected the LPK put the wrong one there, and I didn't know better.

 

[Ninsho]

Doubt it, if it's an A2 stock. If it were an A1 stock and you were using an A2 screw, then possibly.

I don't know how comfortable you feel doing this, but knocking it out and cleaning/polishing the contact surfaces and the recess may be your best bet.

Considering I assembled it, I think I could pull this off. What would you use to polish it?

 

[Ninsho]

With the upper removed, does your bolt catch move back and forth freely?

Yes, it feels a little grainy at times, but it does move relatively smoothly.

 

[vellnueve]

If it moves freely, then it's probably not the catch itself... Mine did that at first but after lubing and smoothening, it was fine.

To polish you can use polishing discs/attachments like found on dremels, but you have to be careful. Progressively finer grit steel wool will also work.

I would say magazines... but it seems unlikely that all your mags would fail at the same time. Perhaps you did install the wrong spring?

 

[Ninsho]

Thats what I am betting on now. What seems weird though is that the first 200 rounds had not a single failure, and this past weekend every single magazine resulted in failure... at any rate next weekend I will try to get to at least one of the two springs (disconnect or bolt catch) and make sure it is correct. If it is then its back to the drawing board.

 

[Dirtypacman]

I had the same problem on my newest build (still yet to post a pic but I will). It happened on about the first 3-4 magazines but I swapped them out and cleaned up the gun and it has not happened again.

So clean/lube it up and mark your mags with tape or something so you can remember the trouble ones if in fact it keeps happening.

 

[Jarhead]

Replace the bolt catch they are 6 dollars and easy to replace. I had the same problem. They do get worn. I assure you that is the problem.

 

[Ninsho]

Replace the bolt catch they are 6 dollars and easy to replace. I had the same problem. They do get worn. I assure you that is the problem.

I just broke 500 rounds through the gun this past weekend, I doubt it could be worn already?

 

[vellnueve]

It could be if improperly hardened.

Can you force it to lock?

 

[Ninsho]

It locks back fine on an empty magazine when I pull the charging handle back, or without a magazine with thumb pressure on the bolt catch and pulling the charging handle. The failure only occurs when firing....

 

[Mike-Mike]

Check to see if the 3rings inside the bolt are lined up. the spaces should be off center of each other.

 

[Ninsho]

Check to see if the 3rings inside the bolt are lined up. the spaces should be off center of each other.

I don't think that is the problem. They day before my last range trip I did check and correct that (I placed the spaces approximately 120 degrees from each other). Unless I am incorrect, I think that is sufficient.

 

[Mike-Mike]

I don't think that is the problem. They day before my last range trip I did check and correct that (I placed the spaces approximately 120 degrees from each other). Unless I am incorrect, I think that is sufficient.

good work