Philip, you need to try out the 375 AB raptor suppressor. The over the barrel component is awesome, but it has a flush mount too. You can get it from 4 inches up to 9 inches long. The over the barrel portion can be 3 inches or 5 inches. you can have a 9 inch long suppressor, with only 4 inches extending past the tip of the barrel.
I also had Justin sip make me a dedicated 416 caliber suppressor, also over the barrel. It will have 5 inches over the barrel, with only 4 inches extending past the tip.. He did it for $1000. I have not received it yet, but there are a few dedicated, large, caliber suppressors, most are meant for 45 handgun, ammo, or either meant for 50 caliber, BMG‘s.