Simply that they are basically two grooves cut into the tumbler to hold the sear nose...and IMO the half-cock notch is not reliable as a true "safety" at all.Robby said:Roundball, I'm not sure what you mean in this statement "IMO, since a tumbler has two identical grooves for the sear nose...half-cock & full-cock...and the design of both notches is identical, neither one of them has any more safety designed in than the other."
As far as I'm concerned it is far safer to have it on full-cock allowing room for a good quality leather hammer stall than it is to rely on a half-cock notch with a bare frizzen.
As long as the frizzen is bare/exposed for a flint to hit it, I don't care which notch is being used, it's significantly less safe, compared to having a frizzen covered with a hammer stall.
With a hammer stall you can sit in your living room and fire it if you want to...not going to make sparks