You don't have enough barrel length in a snubby to get use out of +P.
That's why I won't buy a .357 snubby. All it does is add recoil without increasing velocity.
And you know this how? I've got a spread sheet with all the loads I've tested.
Among the weapons I've tested are a 642 and an SP101 3". +P does better than standard pressure, all things being equal.