Michael, in guessing you mean what's the highest weight bullet you can use in a S&W 9mm compact. If so any weight projectile will work from 115 grain to 147 grain. The only way to find out Wich weight it prefers is by grabbing a couple boxes of ammo in different weights and trying them out. But as long as it's 9mm ammo it will fire any bullet weight safely. Hope this helps.

Michael, that would be 9mm. Or are you talking about bullet weight? It will shoot any grain of 9mm ammo. Have a great day!

The ONLY caliber that should be shot In A 9mm chambered firearm IS 9mm.
If you're referring to bullet weight then the commons are 9mm-115gr-147gr.

Michael, you can shoot through 185gr bullets no issue. The common heavy weight is 147grs : https://aimingexpert.com/what-is-the-highest-grain-9mm-bullet/ -------- Cheers and stay safe!

9mm or the equivalent in inches ~0.355". A 9mm handgun chambered for 9x19mm should only use that cartridge/bullet diameter. A larger caliber should not fit in the first place and would be unsafe to fire in the event that it did.