My take on your question is the use of pistol and rifle bullets in sabots at muzzleloading velocities that only punch a caliber, or slightly over caliber sized hole through a deer's body.
Deer are considered soft-bodied big game animals. Easy to shoot through.
As Ron's bullet testing here at MM has proven out many times, many of the bullets sold to muzzleloading hunters are velocity dependent for expansion.
If the wrong bullet is chosen, it might not expand. If the proper bullet is chosen, and too little powder is used, it might not expand. If the proper bullet is chosen, the correct powder charge is employed, but a long range shot is taken, where the velocity has fallen off to the point below the bullet's requirements for expansion, then the bullet might not expand. If the bullet does not encounter any bone, it might not expand.
Or, the bullet might not expand as much as we THINK IT SHOULD.
At the beginning of the move in muzzleloading to inline rifles shooting saboted, jacketed pistol bullets; a lot of marginal bullets were marketed to hunters under the assumption that since black powder rifles & smokeless powder handguns operated in the same general velocity ranges as one another; it would be OK to put those bullets in a sabot to kill deer.
At the beginning of the 20th Century move to inline m-l rifles, there was a LOT of press touting the sabot/jacketed bullet combo as being FAR SUPERIOR to the patched ball of yesterday.
This is JUST NOT TRUE. A pure lead ball has the ability to kill FAR BEYOND what the ballistics tables would suggest. Ballistic tables were INVENTED/DESIGNED around pointed projectiles.
A ball ALREADY has most of its mass close to its bore diameter. Upon striking a soft-bodied deer, a pure lead ball will immediately start to expand, usually to AT LEAST 1.5 times its original diameter. Sometimes, more. It does this at velocities considered sub-optimal for modern bullets sold to be used in a m-l sabot.
Something to keep in mind....
In the history of humans hunting with firearms, MORE ANIMALS HAVE BEEN KILLED WITH LEAD BALLS, (patched in rifles)(bare in smoothbores), than have been with bullets; by a VERY, VERY, VERY LARGE MARGIN!!!!