AzureRaptor said:
This looks most like an M107, but the barrel appears free-floating, which is a little different...also, no stock, or severely truncated, and no bipod. No reason an equine would have the same requirements there, I guess. Distinctive Barrett muzzle brake though.

Both the M82 and the M107 use a free-floating barrel. Any other point of contact and the rifle wouldn't function, since it relies on a recoiling barrel to cycle the next round and help mitigate recoil. Could also be an M82A2, which would be considerably shorter than the M82A1 or M107 rifles.

AzureRaptor said:Unless whatever this is has some kinda near-magic recoil damping system, Derpy's gonna get eyepunched by that scope. :{ I've seen that happen on both Barrets and something-or-other in .338. You'll remember that for a while, and it's not great for the scope either. :]

Well, she is Derpy after all. Or she'll be alright if she has it tight in her shoulder, shouldn't recoil much then, and when it does, it ought to push her head back with it some, too. That's why I put a Leupold ER/T on mine, it's a good first focal plane optic with a little generosity in its eye relief, so you can keep 3 or 4" between it and you.