AR 15 Bolt lock back

[RussellC]

Just finished my 3rd AR 15 project and noticed something about this gun theat's different from the other two. When I pull back the bolt on an empty magazine, it locked open. My others dont do this, they lock back after the last round wwhen actually firing the gun, but not just pulling back the charging handle.

A co worker just completed 2 builds, and noted one of his did and one did not lock back when the charging handle was used. Both of his lock back fine after the last shot. I have stared at these receivers for a long time and am not seeing a difference, what am I missing?

Wondering,

Russellc

 

[ClickClickD'oh]

Just going to hazard a guess not having seen the rifles, but I'm going to guess that it's one of three things:

1) The charging handle may be out of spec causing you not to be able to retract the bolt far enough to engage the bolt hold open.

2) Buffer of buffer spring may be causing you to not be able to manually retract the bolt far enough, but firing allows the full range of motion.

3) Pull harder.

The rifle should lock open on an empty magazine by operating the charging handle. It's the other two rifles that aren't functioning properly.

 

[GunnyUSMC]

The follower in the magazine pushes up the bolt catch to lock the bolt to the rear. Your gun is fine.
Now if the bolt is not locking to the rear with an empty magazine, you have one of two problems. One could be that the magazine spring is weak and not pushing the follower up high enough to engage the bolt catch. Or you have a problem with the bolt catch. You could have to heavy a spring in your bolt catch or the bolt catch is binding.
Take your upper off and with the mag well empty, push on the lower part of the bolt catch. It should move in depressing the spring and the spring should push it back out. If it is binding a little just apply some oil and work it back and forth.

 

[RussellC]

Thanks. Oddly, the one that holds back uses a piece of crap charging handle until a better one can be had. As for the "misbehaving" rifles, they shoot perfectly, tons and tons of rounds with never a hickup (except this)

Pulling back on the charging handle farther and that isnt it, exchanging charging handles between the two made no difference, The one that locks back locked back the other still did not.

Now, I try both the bolt carrier assembly and the charging handle, and still no difference, "lock back" gun locks back, other does not.

I inclined to go with the idea that it has something to do with the buffer springs position. Since there is no other function problem with either gun, I am not going to bother with exchanging the buffer, springs and buffers. Since I see no way to adjust it, they both have the same buffer tube, buffer and spring.

Russellc

 

[RussellC]

The follower in the magazine pushes up the bolt catch to lock the bolt to the rear. Your gun is fine.
Now if the bolt is not locking to the rear with an empty magazine, you have one of two problems. One could be that the magazine spring is weak and not pushing the follower up high enough to engage the bolt catch. Or you have a problem with the bolt catch. You could have to heavy a spring in your bolt catch or the bolt catch is binding.
Take your upper off and with the mag well empty, push on the lower part of the bolt catch. It should move in depressing the spring and the spring should push it back out. If it is binding a little just apply some oil and work it back and forth.

You hit it right on the head. When I exchanged magazines, the non locking gun locked! All are P mags, but there you go! The gun that locked back from the beginning works either way.

Russellc

 

[GunnyUSMC]

Most problems with ARs come down to two things. Magazines and Operators.

The mag that is not working may just need cleaning. Remove the floor plate ane remove the spring and follower. Use a toothbrush or AP brush and scrub the inside with warm soapy water. Clean the other parts too. Dry everything and wipe the spring with a oil rag. Use a dry rag to wipe the spring off. Put it back together and see how it works.

 

[Jackal]

Its supposed to lock back on an empty mag.

 

[DougW]

Never had that issue on the 28 rifles I have built.

 

[RussellC]

They all lock back now. They always had in actual firing. I don't even know which mag was the culprit as they all seem to function fine now.

Russellc

 

[LUCKYDAWG13]

They all lock back now. They always had in actual firing. I don't even know which mag was the culprit as they all seem to function fine now.

number your magazines to find the bad one