Choke is a reduction of bore diameter,at the muzzle,which is oft touted by Purists. It's never made a fhuqk to me and I'll happily chop spouts well shy of same and never not for the better. Hint.
That being said,I've shortened from the chamber end too,in order to retain said constriction,but will never not bank upon rigidity,which is simply a function of the relationship of length to contour. Hint.
Chamber chopped. Hint.
18" for me. Hint....................