A2 buffer w/ spacer in a carbine buffer tube?

[QuadCam]

you can get this:

http://www.vltorstore.com/products/A5-Re...-Tube.html

and this:

http://www.vltorstore.com/products/A5-Sp...r-Kit.html

this will gie you a rifle weighted buffer with the rifle spring in a slightly longer (.75" than carbine) receiver extension.