So i'm trying to find good loading data for 147gr Frontier CMJ RN bullets with N320 powder for suppressed usage with pistol caliber carbines, Form 3 auto guns as well as supressed Glock 17s.

The issue is when i put in the data that seems to be popular for 147gr RN bullets that is 3.4grain of N320 powder into reloading calculators like "QuickLoad" and "GordonsTool" it tells me that the load is deemed barely safe.

Again what i want to load is:

Bullet: Frontier CMJ 147gr round nose
OAL: 1.135"
Powder: 3.4gr VV N320

Can anyone here confirm that 3.4 grain of N320 along with a 147gr RN bullet at a OAL of 1.135" will be a good choice for making a reliable and quiet subsonic 9x19mm load, should i consider going 3.5 or even 3.6 for the sake of having enough force to cycle the action more reliably?

I know this is an old post but I've had great results with 3.6 grains of Titegroup behind 147 grain Xtreme plated HP. 100% reliability in my XDm with 2 different full size cans and very quiet. So far it doesn't seem overly sooty or dirty at all, though I've heard titegroup doesn't do as well with exposed lead i.e. a little bit more smoke and fouling

Personally I would go with a slower burning powder, if staying in the Vihtavourri line, like the N340/350. Allows you to load closer to the speed of sound while staying safe. Not familiar with the software you are using so can’t guess why its giving you “barely safe”. In any event, you should measure velocity achieved with your barrel at 3.4 grains before upping the powder.