IMO - - -> Between the 20 and the 40 you're talking less than 1.5 inches of bbl.
Just wondering if you can optimize powder for velocity . . . and if so . . . what velocity. Guessing <25fps.
My OEM Glock 6" "hunting" bbl only gained me another 25fps over the origional Glock 20 bbl. This,using a Double Tap 200gr WFNGC (hardcast) load.
I continue to use it for two debateable reasons. Less "felt" muzzle rise and quicker back on target,especially moving target. And hunting the larger boar hogs in thick cover the 25fps gives me extra energy delivered to target. And I feel that I need all I can get. --- SAWMAN