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 Adams Arms bolt not locking (carbine)
Shooter_Mc_Gavin  [Member]
1/20/2012 1:53:03 PM
I have an Adams Arms upper on an M&P 15 SW AR-15 and when you pull the charging handle back (collapsible stock) the bolt lock will not catch in front of the bolt, it will catch the bolt receiver causing the gun to misfire and having the actual bolt sit over the rounds in the magazine causing improper feeding.

I took out my buffer spring and noticed that it is actually a rifle spring that measured around 13 3/4", so I cut about 4 rings off of the spring, now the bolt does go back further, but the spring is just over 10" now and it still will not lock in front of the actual bolt.

My question is, would an actual Carbine spring (i.e. dpms carbine spring) make the difference because it is made for a carbine and not a rifle? The dpms measures in at 11 1/4". Will there be enough spring tension to pull back the charging handle and lock the bolt in the correct position?

On a side note with this upper installed on another AR with a rifle stock it works fine, also with the original SW upper it works fine also.

p.s. Adams Arms has the worst customer service. I sent in an email and called 2 times with detailed voice messages and it is going on 3 days with no reply. I would not purchase another item from them again just due to poor customer service.
Dano523  [Moderator]
1/20/2012 3:42:17 PM
The back of the carrier should be flush with the back of the upper receiver.

If that is right, than you have problems with the math/distance/lenghts of the buffer length, and/or the depth of the receiver extension back of tube void to the face of the front face thread ring on the lower receiver.


So on that note, details on the butt stock on that receiver since as stated that the spring was the wrong one (never clip a recoil spring),and it comes down to either the wrong buffer in play, or you have a knock off receiver extension tube that was not milled/produced correctly depth wise for an AR rifle.
Note,there are two different inner void tube lengths for the AR. The first is the telescoping receiver extension, which takes the carbine spring of around 10.5" (is made of thicker wire), and uses the shorter buffer, then the standard fixed stock tube, which uses the 11.75" spring, and the longer standard buffer. Longer buffer spring in a carbine stock, the spring coil binds up before back of stroke. longer standard buffer, and it maxes out against the back of void before the back can retract the needed distance. Carbine buffer in a full length fixed stock, kill the lower receiver good by, since the B/C will not be limited out correctly on the back of stroke, and the back of the key is going to crash into the lower receiver at the tube threaded section to crack the thread ring in half.

http://www.biggerhammer.net/ar15/buffers/
Shooter_Mc_Gavin  [Member]
1/20/2012 4:51:41 PM
This gun came from SW with a carbine buffer tube, carbine buffer and a rifle (fixed stock) spring on the inside. It worked fine stock, but once I put the Adams Arms upper on the lower receiver the problems I stated above started to happen.
If there is some "knock off" as you state buffer tube on the gun, then it came from SW like that, and that would make me feel like that is another company not to trust to buy from again in the near future.

I 100% understand the difference in size between the actual buffer on a fixed stock and collapsible stock AR-15, what I am asking is if you think the spring tension from the the "correct" carbine spring will make the difference on pulling the charging handle back and locking the bolt into place rather than the problems I am experiencing now.
Dano523  [Moderator]
1/20/2012 11:37:36 PM
Try this,

With a standard gas type upper receiver, and your adams upper allone, pull back on the standard gas system carrier until the back of key is at the back face of the receiver, and then the same on the adams to the back of the pistol block on the carrier, and check to verify that both come about the same distance.

Next, Pull the charging handle all the way back, then reach into the ejection port window and see if you can take the bolt face farther back with your finger to allow the bolt catch to raise in front of the bolt face (while slightly moving the charging handle slightly forward encase it's causing the binding problems).

If you can take the bolt face back farther with your finger than the charging handle, then you have a problem with the charging handle causing wedging problems, or just the charging handle not engaging the carrier on the forward top flat correctly. Here, if you have an extra charging handle, then try to swap it out with the one in the unit.

If you can not take the bolt face farther back by hand, then pull the hammer out of the lower and try again with the charging handle alone. if the charging handle now take the bolt face all the way back correctly, then the Adams carrier may be a tad more rounder/thicker, and the tail of you hammer causing wedging problem between the bottom of the carrier and the top of the trigger and not allowing the carrier to come all the way back to allow the back of the buffer to touch the back of the receiver extension back edge. In cause like this, you can remove metal from the tail of the hammer to solve the wedging problem.


And yes, you need to replace the recoil spring that you clipped.



Shooter_Mc_Gavin  [Member]
1/21/2012 2:03:01 PM
*Fixed*

Measured the inside dimensions of the extension tube from S&W and it was 6 3/4", stopped at the local gun show this morning and bought an extension tube that measured 7 1/8" inside dimension. Replaced the S&W extension tube with the new one and now the bolt locks in place perfectly. It came with a carbine spring/buffer that was pretty cheaply made but I have a DPMS buffer and spring coming to replace it.

What was happening was at 6 3/4" the buffer was bottoming out against the S&W extension tube, if you look inside a stock S&W extension tube it has a beveled cap at the back of the tube making its dimensions just a bit to short for the bolt to travel all the way back.

All in all, replaced extension tube with one that doesn't have the beveled cap on the inside and the 1/4" + I gained made the bolt work perfectly.