Anyone played with barrel length and suppressors?

[fixin]

What would I see the boxed Hornady 123 amax in the 18” barrel with 1:8?

I have had groups as small as 3/4" at 100yds out of my Alexander Arms, and that is with myself and 2 others on the gun. Velocity wise I'm not quite sure, I do not have a chrono to give you that data.