You would need to remove your stock by hyper-extending your stock Lever & remove your stock "very simple" If your stock tube is 1-5/32" outside diameter O.D. if will fit if its 1/16 bigger it will not!
Tim i took off my stock and took off the buffer tube. I'm still so confused its like it has hints of both. In the pic i've post, it has the number of holes that the commercial one but doesn't have the slant back. Its flat black and has the little lip like the commercial one on the threaded part. But it measured 7.25". So i don't know. I went to the Armalite site and they said that they've started using MIL-Spec buffer tubes but they have used Commercial ones.