Actually about an hour and a half. Taking some leave and got to the range today with the M&P .40 along with the .357 Sig barrel. I could only find one box of Gold Dot 125 Gr. .357 Sig ammo locally so I only got 15 rounds down range with that particular ammo and the new barrel. I will say after shooting 180 and 165 Gr .40 loads the .357 Sig rounds do seem "Different". They have a sharper report, and a snappier recoil. You can tell that the slide is moving faster, but there seems to be less muzzle climb. So, it's not like it feels like the recoil is heaver, just different.
Kept a couple targets but can't tell you which holes belong to the .40 round and which are .357 Sig. It was shooting to the same point of impact at 15 yds as the .40 rounds. and I put the .40 barrel back in and kept blasting. I used American Eagle 180gr, Magtech 180gr, Winchester 165gr and PMC 180gr.Put over 150 round through it.
Everyone likes pictures so here you go: