Can the S&W 659 shoot 9MM +P ammunition safely?
The S&W manual says not to use +p. But from what I have read a small amount of +p wont damage your 659. I myself only use +p ammo in the firearm that I carry for self-defense. I practice with regular 9mm full metal jacket ammo But I always fire a few rounds of the +p ammo to insure that it functions in my carry guns. I hope this is of use to you.
Welcome to the S&W Forums. The Model 659 has a stainless steel slide and receiver, it was the predecessor to the Model 5906. The Model 5906 can digest lots of +P ammo, so can the Model 659. Even the aluminum alloy receiver models will hold up to +P ammo, but will suffer receiver damage sooner than those with carbon or stainless steel receivers.
I would recommend frequent replacement of the recoil spring, using either genuine S&W springs or those from Wolff. With +P, I would not run more than 3000 rounds of +P before replacement. Springs are cheap, cracked receivers are expensive to repair and sometimes cannot be repaired or replaced.
Does one really need +P 9x19mm ammo these days? My answer is that with modern bullets like the Federal HST, Remington Golden Sabre, Speer Gold Dot, and Winchester Ranger-T, the answer is no. Higher velocity with these bullets usually results in faster expansion, but sometimes less penetration. The extra recoil simply does not result in better performance from modern self-defense ammo. Older hollow point designs from the 1980's through about 2000 do benefit from the extra velocity.