Buffer tube difference

[will92104]

I just got done with my build and the bolt catch will not catch on the bolt face. It catches on the bolt carrier body. I had the wrong buffer spring and buffer so i changed it out to a DPMS 308 buffer spring and 308 buffer. I did not bother to change the buffer tube. No joy, still catches on the bolt carrier and looks to be about an inch short of catching on the bolt face.. The bolt carrier is bottoming out inside the buffer tube. buffer tube is from DPMS. Have never fired the weapon, have only had an empty mag in it. Is the ar15 carbine buffer tube the same as a 308 carbine buffer tube?

Edited September 4, 2013 by will92104

[DNP]

Tubes should be the same. Are you using a carbine buffer and spring? Snap a pic of the issue if possible(and the parts) and someone will have your solution right away.

Edited September 4, 2013 by DNP

[98Z5V]

You gotta list your specific parts, brother.  What receiver extension (buffer tube), what buffer, what buffer spring, etc. 

 

Armalite AR-10 Carbine Receiver Extensions (buffer tubes) are longer than standard AR-15 carbine receiver extensions.  That's a cause of a lot of hangup, right there, when just getting parts and assembling them.  If it's not a collapsible stock setup, but a fixed stock setup, then there are other issues to figure out.

 

Post the specs/details on the parts used, and we'll go from there.  <thumbsup>

[Robocop1051]

A picture is worth a thousand words.

[survivalshop]

AR 15 Bolt catch or 308 Bolt catch ?

[will92104]

308 bolt catch. everything is for a 308 except for the buffer tube, it is a DPMS ar15 CARBINE buffer tube. like i said above, i had an ar15 buffer spring and buffer in the tube....so i changed it out for a 308 buffer spring and shorter buffer for the 308. when i charge the weapon it feels like the buffer spring is fully compressing before the buffer gets the chance to bottom out on the buffer tube. How long is the carbine buffer spring supposed to be? 11 1/2 in?

[shibiwan]

I measured the extra (takeoff) 308 carbine spring and buffer extension tube. These are "known good" parts that I took off when I put on my PRS stock on my 308.

 

The 308 carbine spring is about 11" long (uncompressed) and the mil-spec AR15 carbine tube is 7.25" long (total length, including the threaded part). The 308 DPMS style buffer should be around 3/4" shorter than the AR15 buffer.

 

Mark the bottom of the rubber tip of the buffer with a marker or something similar (grease pencil? paint marker? paint? correction fluid? chalk?), assemble the buffer, pull the charging handle fully. Release and remove the buffer. If the mark you made at the bottom end of the buffer did not rub off (slightly) then the buffer isn't touching the base of the buffer tube, which implies the spring is too long and it's binding when it is fully compressed. At full compression, the buffer should still be able to extend beyond the spring and touch the end of the extension tube. You should be able to indentify what the issue is (i.e. spring or buffer) with this test.

 

-S

Edited September 5, 2013 by shibiwan

[98Z5V]

 

The 308 carbine spring is about 11" long (uncompressed) and the mil-spec AR15 carbine tube is 7.25" long (total length, including the threaded part). The 308 DPMS style buffer should be around 3/4" shorter than the AR15 buffer.

 

 

 

Internal depth is what matters here.  The AR-15 part is 7" internal depth.  The Armalite AR-10 carbine receiver extension is 7 3/4" internal depth.

[shibiwan]

Internal depth is what matters here.  The AR-15 part is 7" internal depth.  The Armalite AR-10 carbine receiver extension is 7 3/4" internal depth.

 

That explains the 3/4" difference between the length of the AR15 carbine buffer vs the DPMS style 308 carbine buffer. :)

[98Z5V]

Yep, Armalite AR-10 Carbine buffers come out to the exact same length as standard AR-15 Carbine buffers.    Longer AR-10 bolt carrier needs more room in the receiver extension, so Armalite uses a longer receiver extension.  DPMS-based guns use a shorter buffer instead, with the AR-15-length carbine receiver extension.