I haven't bedded a rifle with it, but something you may want to experiment with first is PC-7 epoxy (I buy it at my local Ace Hardware or Home Depot). This stuff mixes as a thick paste, doesn't run. I've also mixed finely shredded fiberglass with it for various little projects; this stuff takes about 36 hrs to fully cure out, and when it does, it's machinable / rock hard. I'd put it up against acraglass any day of the week, and costs 1/3rd of the acraglass kit.
That's just me though.
NRA fo Life Member