It'll only be shot suppressed.
Cool. I am partial to short barrels… for the last decade one of my primary hunting rifles is a 12.5” 6.8 w/7” can. I don’t like long guns. My latest bolt rifle project is a 16” 6.5CM that started with an 8” can, but moved quickly to a shorter 6” can (Scythe). That rifle killed a cow elk at 302 yards this year without issue using 130tmk at 2750 from the muzzle, and is above expansion velocity out past 700 yards… which is plenty for me.
The difference between 18” and 16” is going to be around 50 fps. If you plug your numbers into a ballistic calc, using 1800 fps as min expansion velocity for match type bullets (ELDM, EldX, TMK, etc..) or 2200 fps for monos, when you hit the number is your maximum effective terminal range. Does 50fps matter?…
This is my real 308 data from a hunting load (handload) shot through a 16” large frame AR with 7” can. It is not a max load by any stretch… mid level.
150gr Accubond at 2675 muzzle = 1800fps at 440 yards (1808 fps)
If we add 50fps of muzzle velocity, that changes to 460 (1814 fps)
This data for for my current atmospherics in the desert and will be better at higher elevation.
Point is, does the 20yard delta matter to you?
I prefer the handiness of a shorter rifle.