AR bolt failure to retract

[noahhh]

Every so often the bolt jams tight in the forward position. It has happened once with an empty chamber and once with a round in the chamber. Extreme rearward pressure on the charging handle eventually pops it free. When in that situation, the bolt retracts a fraction of an inch and stops. The forward assist easily pushes it back into position. Vexing to say the least. The rifle is new, with around 100 shots fired out of it. JSE 20" H-Bar upper, Anderson lower, if that matters.

 

[awptickes]

First: Check headspace, make sure the rifle is safe to shoot.
Second: lubricate everything correctly.
Third: swap the BCG to see what happens, replace individual parts as required.

 

[iH8DemLibz]

Have you done anything to the fire control group that would allow the hammer to be in the fire position with the safety engaged?

Keep in mind, too, that headspace will have no impact on an empty chamber.

Check for gas key/gas tube interference.

 

[outrider58]

Bolt group should be able to fall all the way into battery without any to very little resistance.
Take the upper with charger removed, muzzle pointing down towards the floor. Next, insert the bcg into the upper and let it drop. If it stops short of battery, the problem may lie in the gas tube or gas key.

 

[OrbitalEllipses]

Sticky/tight CH and radial deflection when you grasp the CH will also do this if tolerances aren't where they need to be.

 

[Boss94]

Could be a extractor issue.

 

[Fox123]

Mortar man up!

 

[outrider58]

...and then he was gone.

 

[cms1528]

I assume you built it. Check to make certain that the butt stock screw does not protrude into the buffer tube. That will interfere with the action causing a jam. Its a simple fix if it does, trim a little off so it's flush.

 

[msinc]

The times I have seen this it was always a problem with the gas rings not properly seated on the bolt. One or more are not seated properly in the groove. In the last month I have had in my shop two bad carriers. One was not machined properly, the bolt bore was not right which allowed the gas rings to come out of the groove. The other was not cut right where the key goes and when bolted on the key sat off to one side. Both carriers were mil-spec G.I. parts, not aftermarket. I have been workign on AR's since the early 80's and these two are the first and only bad carriers I have ever seen.
Keys and gas tubes will keep the bolt/carrier group from going all the way into battery, but they generally don't cause hard retraction. At least not what the OP is describing.

 

[noahhh]

Bare BCG drops into place slick as a whistle. Headspace checks out A-ok. Bolt rings ok. Extractor ok. Brass is all full length sized in a competition die, bullets seated just shy of leade.

I ran 300+ rounds through it over the weekend without a stutter (and consistent 3/4MOA groups with 55gr. Hornady bulk bullets and CFE-223). Ran it wet with CLP. Whatever it was, it hasn't raised its ugly head. I'm thinking there may have been a tiny burr or two that just needed to get erased with some use. Thanks to all who responded.

What a hoot this gun is!

 

[outrider58]

Bare BCG drops into place slick as a whistle. Headspace checks out A-ok. Bolt rings ok. Extractor ok. Brass is all full length sized in a competition die, bullets seated just shy of leade.

I ran 300+ rounds through it over the weekend without a stutter (and consistent 3/4MOA groups with 55gr. Hornady bulk bullets and CFE-223). Ran it wet with CLP. Whatever it was, it hasn't raised its ugly head. I'm thinking there may have been a tiny burr or two that just needed to get erased with some use. Thanks to all who responded.

What a hoot this gun is!

Glad to hear. Sometimes a little piece of junk gets jammed up in the works and good going over is all that's needed.

 

[noahhh]

Yeah, I wish all my problems were that simple to fix!!