"Has anyone recovered a powerbelt from an animal, geletin, etc that was essentially intact?" Yes.

"My question for you is: are there rifling marks on the bullet?" Yes.

Without rifling marks, finding the bullet or a bullet hole in the target, is unlikely!

As Murphy said, it is the shape of the bullet nose that determines what the bullet hole will look like.

Take a look sometime at the hole made in a paper target by a GI hardball .45 ACP round. Then compare that with the hole made bya semiwadcutter of the same caliber! The .45 Ball makes a hole about the size of a .38 Special cartridge rim ore smaller. The hole looks more like it was torn out than as if it were punched thru by a bullet. OTOH, the semi-wadcutter hole looks like it was punched out by a full-caliber paper punch.