I've watched all those videos and no where does it say you can use .38 Special, or mention this 'rim locked' issue. That's why I was hoping you could point me to where you saw an official video say it was able to fire .38 Special. Because from reading the manual I would say they don't advise it.
I would hazard a guess the the only issues would be feeding from the magazine, as people have been shooting both cartridges in rifles and revolvers without issue for decades. .38 probably just wont feed reliably from the rotary mag so Ruger advises to not use 'em.
I would hazard a guess the the only issues would be feeding from the magazine, as people have been shooting both cartridges in rifles and revolvers without issue for decades. .38 probably just wont feed reliably from the rotary mag so Ruger advises to not use 'em.