Originally Posted by m&p45acp10+1
. . . the only times I have seen bridging it was in the powder funnel.
Same here. Though I've got ample evidence of having had it happen inside a powder measure, I just can't see it inside there when it does.
Seriously, though, there does seem to be bridging or log jams in some measures with some powders. Call it packing irregularities or whatever you please, it is certainly the case that fine spherical powders will rarely, if ever, have this issue.
A couple of guys in past threads have mentioned attaching a fish tank aerator pump to their powder measure hoppers with rubber bands to act as a vibratory settler. Use a pushbutton switch and just give it a one second push at each end of the charging stroke, one to fill the measure cavity and the other to drop it down the tube.
With completely empty cases you also want to look at the possibility of short stroking the press.