Whose barrel?
You can check the buffer weight by just opening up the upper / lower and looking at the face of it. Unmarked is carbine weight, everything else will be stamped "H", "H2", etc. It depends on the LPK but it's probably a carbine weight.
A cyber guess would be to try an H buffer if you wanted to change it out. Get it dirty, load some mags with one round each and see if the bolt will lock back on an empty chamber. Use the weakest ammo you ever plan on shooting.
Shoot it back to back with the carbine buffer and see if you can feel a difference. Try it offhand and see if you can SEE a difference between the two while looking through your sights at the target (as it fires and recoils).
