yeh I feel your pain, my first zeroing shot with my first .375 h&h was 300 gr mid load while in my fleece. That really thumped.... Used the slip as a recoil pad after that and made a new batch of rounds with quite a reduced charge I might add.
On the op I keep spare bins in the car at ALL times now!
ps:
took the wrong rifle red stalking once, had both rifles out in slips from the night before and put the wrong one back in the cabinet in it's slip. Wouldn't have minded but had the wrong ammo too and on a Sunday so couldn't even buy bullets to try for roe..... genius