I believe +P is NOT safe to fire in a M10-6. M10-7 aren't either to the best of my knowledge. IOW, I would use normal pressure factory spec ammunition. IF you don't care about the handgun or S&W repairs, shoot what you like. I am aware of M10-11 as being OK for +P. There were many M&P M10s that were carried for years. Many LE agencies used to use HOT 38 Special loads that were capable of 357 Magnum pressures and performance. I am simply saying that I wouldn't treat a NIB M10-6 in such a manner. If it is a used and abused example, it won't change the value. In my experience, +P loads simply accelerate wear and tear. I would buy or trade for a M65-3 or later 357 Magnum in 3" form. The M65s have some problems with hot 125 gr 357 Magnums also. If you keep the M10, stick with normal factory ammunition. Trade up if you have to have +P performance or get a 357 Magnum.