I agree right now ammo might be a bigger obstacle than you think
and odds are its going to get MUCH worse before it gets better!
as for making larger holes in barrel, a jig saw can do it, as can an angle grinder with a thin cut off wheel
as well as other tools
but try to not make too sharp of edges or you c n be harming the bears your not after!
filing down edges is recommend by most I know that use them!
or cutting and them rolling edges over so not jagged and sharp!
and just a thought for you
if your using a 55 gallon drum, you can use a shop dolly to move them about,
use a ratchet strap to secure barrel to it, find one with BIG wheels and they will roll a lot easier thru terrain!
you can remove dolly once where you want it
or chain it up with barrel!