This is for information purposes only. I am simply relaying information gathered today from two phone calls. 
KKM: M&P factory production gun barrels are from production runs intended on going into production run guns.
KKM barrels are made to a much higher level of exact tolerances.
KKM barrels should give a 30% smaller group than factory.
KKM will not give group sizes and will only quote a percentage of increased accuracy because of other components that affect accuracy such as locking block and slide tolerances from S&W on your particular gun.
KKM drop in is 175.00 including shipping.
Bar-Sto: Two M&P barrels are currently in R&D. No release date as their production keeps getting pushed back. Drop in barrel should retail for around $215. The gunsmith fit barrel price was not given. Accuracy for drop in 1.5" at 25 yards. Accuracy of gunsmith fit is 1.25" at 25 yards.
What I found interesting about these conversations is my own M&P accuracy. My M&P 9mm FS has seen 2.5 - 3" groups with factory produced ammo (sucks with plated reloads) so a 30% group reduction of that with a KKM barrel should equate to 1.5 - 2" groups at 25 yards. There is the possibility of tightening this up a bit if tolerances in locking block or slide are fine tuned. Then there is load development which might help even further for you reloaders out there. Hmmm something to ponder! 
KKM: M&P factory production gun barrels are from production runs intended on going into production run guns.
KKM barrels are made to a much higher level of exact tolerances.
KKM barrels should give a 30% smaller group than factory.
KKM will not give group sizes and will only quote a percentage of increased accuracy because of other components that affect accuracy such as locking block and slide tolerances from S&W on your particular gun.
KKM drop in is 175.00 including shipping.
Bar-Sto: Two M&P barrels are currently in R&D. No release date as their production keeps getting pushed back. Drop in barrel should retail for around $215. The gunsmith fit barrel price was not given. Accuracy for drop in 1.5" at 25 yards. Accuracy of gunsmith fit is 1.25" at 25 yards.
What I found interesting about these conversations is my own M&P accuracy. My M&P 9mm FS has seen 2.5 - 3" groups with factory produced ammo (sucks with plated reloads) so a 30% group reduction of that with a KKM barrel should equate to 1.5 - 2" groups at 25 yards. There is the possibility of tightening this up a bit if tolerances in locking block or slide are fine tuned. Then there is load development which might help even further for you reloaders out there. Hmmm something to ponder!
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