AR 15 Bolt Will Not Lock back?

[illinoisburt]

If at this point if the gun is running with carbine buffer and spring without issue then maybe the solution is already at hand?

Do we know for sure the tube you were sent was actually a rifle tube and not a carbine tube? I agree the internal depth measurement is called for.

 

[rsrocket1]

While I have successfully shot my 20” upper rifle on my carbine lower without problems, that was with a carbine buffer and spring in the shorter carbine tube.

If you put carbine parts into a rifle buffer tube, the carbine spring with the shortened buffer will be in a buffer tube 2” longer than it was designed to work in. The spring will be less compressed and probably provide less return force. While it would certainly fix the lock back problem, it might lead to short stroking or a weak bolt closure.

Best thing is to make sure the right parts work properly together. While it may be nothing more critical than an annoyance when you’re just putting holes into paper at the range, it can become tiresome dealing with it every time you take your gun to the range.

 

[bfoosh006]

As mentioned earlier, If some how a A2 length buttstock screw was used in a A1 stock ( shorter ) the longer A2 screw would limit travel.

Measure the internal depth of you buffer tube.
And measure the OAL of your rifle buffer.

And Better yet, pics of the buffer and recoil spring ( Maybe a 308 recoil spring ? )

 

[bfoosh006]

I checked out the bolt travel. With the charging handle pulled back, the bolt stops just before the back side of the locking lugs reach the bolt catch.

After switching out the buffer and spring with the one from the carbine, now it will lock back with an empty magazine.

Something certainly off.

And do not fire your AR15 with a carbine recoil setup in a rifle length buffer tube.... the BCG will smack the lowers receiver threads and damage them.

 

[kcofohio]

Take out your buffer and spring and measure the inside depth of your buffer tube. My rifle length buffer tube is 9.5” from the back of the tube to the spring loaded retention pin. My carbine tube measures 7.5” so when you put your carbine spring and buffer into the A2 tube, you have 2 more inches of depth and can easily pull the bolt back to where it locks.

When you put your rifle spring and buffer into that same tube, something is preventing that spring and buffer to compress enough to get the bolt all the way back.

Either the spring dimension is wrong (unlikely) or there is something wrong with the buffer tube. It could be an obstruction or a bend. You should get a flashlight and examine the inside of your buffer tube. Also measure the inside depth just to make sure.

I took the buffer and spring out. The tube measured 9".

Then I removed the screw for the stock. And it measured a little over 9 1/2".


And looking at the buffer, I can see where it has been hitting the screw. Now to cut the screw down.

 

[kcofohio]

The buffer tube, buffer, and spring came as a set, with a spacer for A1 style stocks. Not sure why it didn't come with a separate shorter screw.

 

[kcofohio]

I cut about a half inch off the screw and reattached the stock. It now locks back on an empty magazine. Mystery solved.


Thank you all for your input! And I did learn a few more things.