Tam says (referring to the RAA PDS) …

Look, if you’ve just gotta have a gun with a piston in it so your friends will know you’re cool, get a gun designed from the ground up to use a piston, not some kludge affixed to a Stoner-type bolt carrier assembly that was never intended to have a foot-long lever torquing it from the top.

Read the full post and the comments here.