While I haven't shot balls though a choke, it's no big deal. My hunting friends did shoot the undersized .685" balls through their full choked duck guns. Howard used thin cloth patches on the balls, that he could 'just' push through the choke in a test. On target, he was getting 4" to 5" at 50 yards with just the twin beads on the rib as guidance.
; Back when Winchester loaded balls for use in chokes, they used only .64" or .65" cal balls that would easily drop through a 16 bore's barrel. It is no wonder they weren't accurate at all.
; Came across an aritcle by Gil Sengal (someone might have sent this to me) in Handloader magazine, some years ago. he used the same system I did, with the cas check from a trap wad for holding the ball centered. He was using bore sized balls as well. He also used normal Fed trap wads, wth the petals cut only 1/4" to 3/8" high. These helped centre the ball as well. I had some old style 2 piece wads in which the base section acted well for centering the ball. I usupect the BPGS gas checks, if loaded upsidedown would do the same thing. It is imperative to hold that ball in the centre, somehow - if it is at all unersize. Even a bore sized ball may benefit.
; Just finished cutting off the cutt's comp. from my old pump Mossberg (full 3/4 stock with bolt-like action), sweating on a front sight and reversing a BSA elevator sight from a M30 Reminton Enfield. I haven't measured the bore yet - will check out those 'aspects' today and cast up some .725" balls in hard lead.