i wouldn't blame the bullet... all bets are kinda off when a poor shot is made. every bullet is some type of compromise.... find the compromise that works best in your head and roll with it. i like monos, but i understand their downsides, and when i have shot them, i accepted their potential downfalls.
sounds like the exit hole was actually pretty dang good, so can't even chock it up to the bullet under performing due to shot placement. sounds like the bullet did a good job considering the shot placement.
make sure you have a rest to shoot from next time, bullets work better through the lungs (not being a smart ass or high horser, i have made bad shots too, but blame myself for them, not the projectile)