Yeah, brass will come down and as long as you have bullets and powder/primers, brass is the easiest I've found. I just bought factory loaded ammo until Lapua made brass for it then got that...
My experience with .300 BO is that it wouldn't even be all that great for zombies.Go for the Grendel, hard to beat for your tasks, my opinion .300 BO is useless unless subsonic for zombies. My son shoots an ARC its a sweet round, I have a Grendel, I feel it's better all around because of the heavier bullets... It's a very fun and capable little cartridge!!
I understood it differently. Then with a maximum range of 75 yards then you should be pretty all right on all of them. When it said the range of 550 and generally no more than 75 yd, I took it as a range of 550 yards mostly within 75 ydIn the OP, what I had meant by "550+ range" is the size of the bear, not the max distance to target. I had written that shots would be no more than 75 yards. They are generally closer than 50 yards, because outside of that distance we tend to fire a warning shot to discourage any further encroachment on the pens. With bears, this works most of the time.
I've made the decision to go with the Grendel. My AR10 is in .260 Rem, and I shoot a lot of 6.5x55, so have plenty of different 6.5 projectiles on hand. It's not a matter of switching between different projectiles for this particular rifle; my wife isn't going to ID the predator and then choose the appropriate ammo, nor does she want to think about selecting between different rifles; she wants to shoulder a dedicated rifle and go, and it will be a one-size-fits-all projectile. Likely, it will be a 120 TSX. I'm not a fan of pass-through shots, particularly because I want to be able to verify that the critter is down for the count, and I have been using Barnes for years to do this. It's usually one and done.
Reloading my own ammo is an absolute requisite, which was the issue holding me back from the Grendel initially (due to lack of available brass). I'll just keep looking. I use a lot of Starline; perhaps they'll have it back in stock sooner than later.
Just for reference, the AR10 is too large for her to shoulder and get her eye behind the glass, hence modifying the existing AR15 for this purpose. It's the perfect LOP for her. The next step will be getting the barrel and bolt head on order. Remarkably, we've had relatively little predator activity so far this winter (if you can call it "winter"; I've counted at least ten days in which tree frogs have been peeping between Jan 1 and now, and normally we're averaging 25 - 40°F daytime highs; they don't generally become active until the temps are mid-60's).