I have several hundred once fired berdan primed bmg brass. Is it feasible, or possible to convert to boxer primers? I'm confident I can rig a jig to drill the flash hole. Are the primers even the same size?

I don't know if the primers are the same.  Berdan LR primers are, IIRC, slightly smaller than standard LR primers.  You could make a jig to drill the FH and then pry the primer out with an awl probably.   Getting the primer pocket the correct size for the #35 primers might be the hard part.  You might have ALOT of time involved.  You might have to have a custom reamer made to cut the primer pockets the correct size($$$).  Might not be worth it in the long run.  Maybe you can sell your brass for some decent money and just buy some brass.  

don't need a custom reamer. use a 5/16 reamer and reamer stop. I dunno what size berdan primers are in 50 bmg but if the are slightly smaller this could be a easy way to come up with usable brass.

The first thing todo is to determine the size of the berdan primer

Jason

Just curious, but I'd make sure the case head and webbing are the same between the two.  Having weak brass from something like that could be bad for you and your equipment.  My guess, yeah, it'd be close enough.  Probably the only way to tell would be cut a boxer and a berdan in half (cross section) and compare.  Maybe you could find a worn out boxer piece to cut?

Gundraw

Some berdan brass has the primer anvil molded as part of the casing is this the case w/ the 50BMG stuff?

its my understanding that all berdan cartridges are of the same general construction. with the anvil in the center of the primer pocket what he'll have todo is either remove the anvil with an end mill as I suggested above for opening the primer pocket to the correct size and then drill a new flash hole in the center.

Jason