I think BSA made barrels for Sten guns but the piece was so simple that much of the rest of the gun was put together at auto body repair shops. Probably the same for the PIAT based on what they look like. I have seen what must have been an experimental No.4 rifle which had a floorplate, triggerguard, and other fittings apparently made from sheet metal on a press brake, not like the nicer stamped parts on Mausers and Springfields.

I don't know when Miyata started making rifled bikes but I was under the impression that it was some time after they left the gun business. I always thought that perhaps they were inspired by their gunmaking past but that was the extent of it.

Not at all sure but when they were making guns, I think the state of the art was probably to cut rifling, whereas the bike tubing was probably made by drawing a mandrel through the tubes, similar to more modern "button" rifling. I guess I don't know when they came out with the tubing, when button rifling started to supplant cut rifling, or when Miyata left the gun business, if they did at all, so my suspicion may not hold any water.