I purposely left out any refs to the English M/C's, having owned and ridden more than a few. FWIW, the last BSA 441 Victor that I owned had a set of fancy Italian forks on it that started w/a 'C' and was still lookin' for a place to high-side itself, but wot caused my losing it to another individual who knew not squat about them, but was enamored w/it's pretty polished aluminium & yellow painted gas tank, was the last kickstarter pinion gear that I had to put in it at a cost [cost for the part alone, that's wholesale, not retail] in them days of $US 119.00 I have, to this day, a ganglion cyst on a tendon from another English bike [an Ariel 500] where it revolted at an inopportune moment and then had an AJS backfire under similar conditions at another time, just to be sure it took. My chosen Converse sneakers of the time provided zero protection from such excursions in bad timing. The 441 Victor's were prone to the the same antic's, except that they frequently broke the pinion gear as as result. And I could, but won't tell you some tales about ownership & riding older BSA Gold Stars [B34's] & doing hill climbs at places like Mineral Wells, TX in the late 50's & early 60's, but I shant.
Also: A-10 cranks in 650 unit constructed 650's made for some very competitive '650' flat trackers, that weren't quite 650's any longer, but that's a whole dif subject.
I still have no idea what a BSA 500 shotgun looks like.