Yeah I think your barrel was extended, welded and threaded. I think thats why its thicker there. What I meant was to order a non-threaded factory M&P9 full size barrel and have it threaded at ADCO. I'm trying to figure out if the M&P9 full size barrel would function correctly in a compact M&P9
UNless thats how every barrel is made....
All M&P barrels are machined by the factory in this fashion. They have a bulge at the muzzle that facilitates lock up with the slide.