Prepping for never being able to get .30-06 ammo again, but wanting the ability to shoot a valuable collectible firearm for all of the forseeable future?

Or prepping for bugging out/in during apocalyptic times, and the BAR is to be a weapon of choice and will need to be thus fed with the food the other firearms get?

Either is a legitimate answer, but will steer the conversation differently.

Since it appears the BAR is not yet acquired, the budget necessary to acquire one can usually sustain the means to acquire or make a sizable stash of the correct ammo.

I apologize that I'm not answering the question, but I'd hate for someone to make such a drastic alteration to a collectible firearm before making sure they really want to do it. It's still certainly your call with your firearms.