AR cycling issues

[Tisto]

I have an AR that has had problems with the bolt going fully into battery. At that point, the bolt gets stuck and is very hard to open. I always thought it was a very tight chamber causing the problem.

I replaced the entire upper with a new one from a different manufacturer. Taking it to the range for the first time, I quickly had the same exact problem. At this point, I swapped lowers with a friend, and the problem disappeared. I used the same magazine.

I will take the original upper to the range with a different lower and ammo I know it didn't like to prove my theory, but at this point I have no doubt about the lower being the cause.

What parts in the lower do you think are causing this ?

 

[dsdmmat]

The lower receiver could be out of spec. Did you build this lower from an 80% receiver.

are there wear marks on the bolt carrier tail from it rubbing on the buffer tube?

 

[Hochulsucks1234]

I have an AR that has had problems with the bolt going fully into battery. At that point, the bolt gets stuck and is very hard to open. I always thought it was a very tight chamber causing the problem.

I replaced the entire upper with a new one from a different manufacturer. Taking it to the range for the first time, I quickly had the same exact problem. At this point, I swapped lowers with a friend, and the problem disappeared. I used the same magazine.

I will take the original upper to the range with a different lower and ammo I know it didn't like to prove my theory, but at this point I have no doubt about the lower being the cause.

What parts in the lower do you think are causing this ?

Is it a carbine build? Are you using a rifle buffer and spring?

 

[Zerex]

Factory ammo, or your reloads?

 

[Mosinitis]

Had this happen. Check the lower receiver for primer stuck under the trigger. Take your time, use a flashlight. They can be well hidden. Make sure you get both anvil and the cup out.

You can make a tool from a paper clip to fish out stuck primers.

 

[repete]

Does the lower have a fixed magazine? If so I'd try a different mag.
Mosinitis has a legit point, be pretty rare but I could see it happen, especially with reloads.
Also if this is an 80% perhaps the hammer hole is a tad high? (I'm reaching here)

 

[dsdmmat]

Another question: new problem or been there from the beginning?

 

[dwa12479]

Is it a carbine build? Are you using a rifle buffer and spring?

A rifle length buffer in a carbine tube wouldn't allow the bolt to open fully. The rifle would never have run at all.

 

[kev74]

2 uppers won't work on one lower, but will work on another lower?

I think I'd start by gutting the lower, cleaning it well, looking all the parts over carefully, then reassembling.

 

[Drinkthekoolaid]

Dumb question but I'm curious
Are there any obvious defects or parts broken? Everything clean and lubed?

What length barrel?
What length gas system?
What buffer and spring?
Was it only malfunctioning with a specific type of ammo?

 

[Beerman]

What brand lower, what brand parts are in it, who built it, did you get it all new or is it used, etc? That lower is ganked. Needs to be dismantled and reassembled. Put a different trigger in it (if you have one sitting around) and run it again.

 

[Tisto]

Ok, here's the update: I took the two uppers to the range with a lower from a completely different gun. Both of the uppers ran every ammunition I fed them, although one particular load was finicky in both. The newer upper had a couple hiccups, but I subscribe them to the VERY stiff bolt needing a few hundred rounds of breaking in.

The "bad" lower is going to be stripped and given to my friend's kid. He has a Cerakote business, and will make it pretty for display. In return, I will get him to do a nice camo job on something for me.

I cannot find exactly what the issue is with the bad lower. It may be a few small issues adding up to a problem. What I can say is that it is more difficult to push the takedown pin in and out than with other lowers, and pulling the bolt back with the charging handle is also much more difficult than with other lowers. I believe the takedown pin hole is a few thousandths off, and that the buffer tube does not sit perfectly inline with the bolt travel. I'm done messing with it. This is the only one I've ever had that has caused problems. Replace it and move on. Life's too short to get all jacked up over a $60 part.

 

[FP1201]

I've had problems like you describe with 80% lowers, especially ar10 variants... usually end up using a round file (Chain saw File) to alter the take down pin hole, also have block sanded the top of the receiver to bring it closer to the upper, and with the 10's I've had to take material off the top of the extension tube for uppers to properly mate together.

 

[repete]

Ok, here's the update: I took the two uppers to the range with a lower from a completely different gun. Both of the uppers ran every ammunition I fed them, although one particular load was finicky in both. The newer upper had a couple hiccups, but I subscribe them to the VERY stiff bolt needing a few hundred rounds of breaking in.

The "bad" lower is going to be stripped and given to my friend's kid. He has a Cerakote business, and will make it pretty for display. In return, I will get him to do a nice camo job on something for me.

I cannot find exactly what the issue is with the bad lower. It may be a few small issues adding up to a problem. What I can say is that it is more difficult to push the takedown pin in and out than with other lowers, and pulling the bolt back with the charging handle is also much more difficult than with other lowers. I believe the takedown pin hole is a few thousandths off, and that the buffer tube does not sit perfectly inline with the bolt travel. I'm done messing with it. This is the only one I've ever had that has caused problems. Replace it and move on. Life's too short to get all jacked up over a $60 part.

Every thing could be in place and within spec but if several things are just barely in spec the total amount could be what you've been dealing with. Good use of the lower!