I sat the other day casually shuffeling some 50BMG cases around while dismantling a cal. 16 boltaction gun. Hmmmmmmm that 50BMG case fits "perfectly" on the boltface, (insert sound of loud bowelmovement in head here )
Why not slap a 50 cal barrel on that gun and make a "wildcat" of it using 50 tracer (12.7x76)?
Today i figures i'd convert some cases for shotgun primers and this is where the project ground to a hold

It uses an unholy large primer (ø .315"x.215) and there's some tube inside the case, so converting is going to be a major task.
Is this to insure proper ignition of the tracer bullet?

Those are 50cal spotter cases with a flash tube;
not what we think of as regular 50cal BMG.
The spotters I've seen don't have that tube.

Shotgun primer won't have enough power to ignite
charges of rifle powders through that tube. There are ways-

First you could strengthen the firing pin or hammer
strike in your gun to fire the big BMG primers.
Like I did on NEF and Savage for our 12ga FH

Second you could get rid of the tube or get cases
without tube, put in bushing and use shotgun primers
with IMR 4759-4227,VV110, or RE17 rifle powders, that shotgun
primers would fire off ok, as we did in our
12ga FH research. Ed