Muzzleloader rifles are very individual weapons, your rifle may like a particular bullet and load, while your buddy's rifle of the exact same make and model won't shoot it for crud.
I've personally had trouble loading the Powerbelts into my rifle. I have a friend who shoots the .45 cal Powerbelts, aerotips and he's had two deer hit right in the pumphouse that I thought went way too far. He's killed others pretty dead though, but one of those deer I witnessesed him smack at about 50 yards and I was not impressed. I'm not sure if what I witnessed was more of an indictment of .45's in general or that particular bullet. Like what you describe, right through the ribs, no bones hit and the deer didn't even act like it was hit for about a minute.
It's hard to get a mz bullet to expand really well, at "normal" deer hunting ranges, save for the Barnes Xbullets type rounds.
Hunters have killed tons of deer with those Powerbelt bullets, no doubt.
Personally, I consider saboted bullets made of solid lead to be superior to jacketed mz bullets, which sometimes act like full-jacketed rounds and just punched holes in deer I've shot with them.
Now, granted, they were BIG holes and the deer did die.
But, I think solid lead gives better performance at longer hunting ranges, than many of the jacketed type bullets I've used. Lead bullets at least expand a little bit at extreme ranges I get antsy shooting at deer when I'm not certain I'm getting at least some expansion. Plus with some of these custom type lead bullets, you can get get far superior BC's in mz bullets over a lot of the jacketed type bullets. This generally lends itself to better accuracy and more retained energy downrange, so again, with solid lead, you should get better expansion at those distances.
Here is a link to
some bullets I like.