Primarily the suppressor will be attached to an MPX-K. ideally Id like the ability to shoot it on a G19, but if it doesnt make any sense, then so be it.

What is the go-to recommendation for something like this? I previously built my own 7.62 titanium can (legally with a F1) using 1.625" diameter and OAL of 8", and its worked really well. I think I plan to make a 9mm one, but am trying to determine what diameter to work with.

suggestions?

For pistols, 1.37 seems pretty standard, though subgun cans often go quite a bit larger, 1.75 or so.

How much do you care about being able to use iron sights on the pistol?  If you dont care, go for as large a diameter as you want.  My Rex can at 1.7 exceeds the performance to the naked ear of my dead air wolfman at 1.6ish on my MPX.  No experience running these on a browning style pistol.