I have personally run 50 or so through deer and gutted and butchered those deer myself. I have loaded for others rifles at least another fifty that accounted for dead deer and I have examined carefully all but one or two of those. I have seen zero evidence of failure to expand. I have seen two recovered bullets, one recovered in the deer, and one recovered in the dirt after penetration.
Calibers have ranged from .223 to 50 ML. ranges have been from 25 feet to almost 300 yards. The average distance at which I have killed deer with them has probably been between 100 and 150 yards. The bullets have included early Xs, XLCs, TSXs, TTSXs, T-EZ, TMZs a few E-Tips and a few GMXs
25 samples of most things is enough to give you a pretty good idea of consistency.
The only minor expansion of Barnes bullets I have seen have all been stuck backwards in trees after going through targets and backers at the range. The only bent mono bullets I have seen were after the same thing. I have been loading since 1956. Since the same time I have been skinning deer and not just my own. It was the kids' job to skin what got shot that day after dinner. So, I have seen what a lot of different bullets can do. I have yet to see a cup and core bullet perform anywhere near as consistently as monos. I have very little experience with the best of today's bonded cup and cores however.
Were I to recover a bent bullet from a deer, a minimally expanded bullet or a non expanded bullet, before I blamed the bullet I would have to be damned sure it was not a case of pilot error AND that there was no other possible explanation based on the numbers of them that have killed deer after I worked up the rifle and load. Based on seeing more than one person claiming to have had more than one failure, and so many more having never seen evidence of even one failure, I have to just as someone trained in statistics be VERY suspicious of pilot error in those cases. I would need to see that ALL of the bullets that failed came from one box of factory ammo or one lot of bullets before I'd start to give equal credence to that possibility as pilot error.
Monos are certainly longer for bullet weight than cup and cores. Lead is denser than copper. It would not surprise me even a little for some of them to not be stabilized or marginally stable. If a target backer is enough to destabilize a mono and I have seen that happen, then hitting anything with a little moisture in it like a fat prairie grass stem or blackberry bramble could certainly do it as well. Could it do it more readily with a bullet that was barely spinning fast enough to stabilize it? I do not know, I never tested it , but it seems logical. I find it very hard to think of a situation in which a mono could hit a deer point first tumble after some distance inside a deer and retain the energy to bend the bullet. That takes some serious explaining.
