There has been a lot of discussion around the ‘net over the past few years about the poor accuracy of many of the S&W M&P 9mm pistols. Supposedly this is because of a rifling twist rate that was too fast for the lighter bullets.
Recently Hilton Yam posted on the 10-8 Performance blog that the newest, 2012 production M&P 9mm barrels appear to have a slower twist rate, closer to that of the KKM aftermarket barrels, which is resulting in great accuracy (Yam reported 2.5″ at 25 yards, my M&P9 Pro is just a hair tighter than that with 115gr ammo). You can find the 10-8 Performance blog here: http://10-8performance.blogspot.com/2012/06/s-m-barrels.html.
Today I compared the barrel rifling from my 6/2012 production M&P9 Pro to that of an early 2010 Production M&P9, and I could see no discernible difference in the twist rate between the two barrels. I’ve contacted 10-8 performance to see if we can get a couple pictures down the bore comparing the different rifling twists that they are seeing. Definitely seems that something is up, and S&W may be changing something with these barrels. Maybe some have a different twist, and others do not? I do not know.
Anyways, here’s the sub 2.5″ group that my friend Tom shot using my M&P9 Pro. Ammo was 5 rounds of 115gr Winchester white box FMJ shot at 25 yards. Pretty impressive if you ask me.