I wouldn't even consider shooting at anything living with a rifle I hadn't tried for myself on a target first. I have a number of shooting friends and although some of us can rifle share, others cannot. The chap I usually shoot foxes with is much taller than me and I need to aim about 4" off when shooting his gun to hit what I'm aiming at. He's a good shot as am I, but I guess we must have a different trigger technique, cheek weld or something? I don't know, but we can only share a gun because we know from experience how it will shoot.
When paying $10,000 for a buff and another $1000+ for flights what's $20 or even $200 in ammo to make sure that rifle is hitting exactly where I think it is? If you wound your trophy because of that and either lose it or get tossed, you'll wish you spent the money on the ammo. I wouldn't risk it, no way! The only time I'd have a go is if I was in a bad situation and had to pick up another man's gun and do my best with it, but then I wouldn't have any choice.