just my thinking: what if, at the paint shop, they had a pressed plate that fit over the rim (two halves ?) and then painted the center. Remove the shells and paint the next one and so forth. Next off to the red stripe paint station where they have two rollers with a crank handle, also a comfortable plate to rest ones hand that held the brush, spin the rim while holding your hand still and paint the termination red stripe. Job done and no awful masking tape. The stuff I remember, back in the '60s, was the white ish sticky stuff that was just awful. Just thinking out loud here...Another detail about likely masking before sandblasting and lining in the factories: What was available in 20ies and 30ies for masking tapes - if at all?? I only remember from youth these horrible texile black sticky tapes electricians had in 50ies . Not very suitable for masking in paint shops I think. So how did they apply lines or paint fields on tanks, chromed or painted ? Even today lines are painted by orientation on chalk lines or some such, no masking tapes anywhere, see YT clip at the Enfield factory in India - pure art !!
Vic
tank lining India:
tank lining
Enfield hand lining