Its funny, but I forget if I found any repros that floated, but most likely not. I never found that repro you pictured James.
But even without the float test, there are no Leia Blasters without the circle on the magazine.
Even the first shots had that mark.
So far, knock on wood, I haven't see a Leia repro with that marking, but there is some grumblings I heard over on FB that there may be some new ones on the horizon. I will only believe that when I see it.
All that said, it could be possible that there was a short shot blaster out there where the circle never formed properly, but I would expect there to be a sign of a short shot being a depressed area.
dienstuhr, I'd say 99.9% that without a circle it is a repro. But post a couple pictures if you want to be 99.99 to 100% sure.