If blowing off the front end off "impedes penetration," I have somehow been lucky enough not to see it matter, after witnessing around 200 Nosler Partitions take big game animals over the decades. Here are a few examples:
A 400-grain .416 I put just behind the ribcage of a running-away Cape buffalo ended up in the shoulder on the opposite side. A 150-grain from a .270 Winchester did the same thing to a quartering-away bull moose here in Montana.
A 100-grain .25 from a .257 Roberts broke the right hip of a pronghorn buck and ended up in the left shoulder.
A 140-grain from a 7x57 placed in the middle of the chest of a facing mule deer buck was found in one of the round steaks from the rump.
A 180-grain from a .30-06, shot at a big bull kudu standing on a steep hillside 350 yards above me, broke the near shoulder joint and the spine before ending up under the hide on top of the far shoulder.
A 225 from a .338 Winchester Magnum broke the right shoulder joint of a huge bull musk ox and ended up at the rear of the ribcage on the other side.
Those are ALL Partitions recovered with NO front core remaining intact. Numerous others probably lost their front cores but exited. Among those were a 200-grain from a .300 Winchester I put into the big shoulder joint of a 6x6 bull elk at only 75 yards, so the bullet hit at almost muzzle velocity. It smashed the joint, traversed the chest, and exited at the rear of the ribcage on the other side.
Aside from all those examples, as I pointed out in another post the Partitions over .30 caliber have the partition moved forward, and are designed to retain about 75% of their weight even if the entire front core disappears. It rarely does, but even then they continue penetrating. A good example is the 286 9.3mm that broke the big shoulder joint of a big blue wildebeest almost facing me at 200 yards, and was found under the hide of the opposite flank, maybe a foot in front of the ham--without the front core, retaining 74.1% of its weight.
Now, Nosler Partitions are by no means the only premium bullet I use, but I have used more of them any other because they've been around longer, and were the only one readily available when I started feeling the need for deeper penetration in the mid-1970's, when I was hunting elk in the thick, steep Montana mountains near the Idaho Panhandle. Back then the 200-grain .30 was a "semi-spitzer," which didn't matter where ranges were normally under 100 yards. Dunno if they lost the front core, but don't really care, because they exited everything, including a mule deer buck weighting at least 300 pounds shot lengthwise. I've used the 200 Partition to take more elk than any other bullet, and would use it on 99% of the big game animals on earth.
I have since used numerous other premium bullets considerably, including the A-Frame and both versions of the Swift Scirocco; Barnes X's from the plain original version through blue-coated XLC to the TSX and TTSX; Speer Grand Slams; Hornady Interbonds and GMX's; Norma Oryxes; North Forks; Trophy Bondeds from Jack Carter's original model to the latest tipped, nickel-plated, grooved-body version by Federal. Have even used Nosler AccuBonds on animals from deer to a grizzly bear, and have taken over two dozen animals from springbok and pronghorn to blue wildebeest and 6-point bull elk with E-Tips. Would quite happily use the vast majority again.
Some have out-penetrated Partitions, though not by all that much, though some definitely punch through the hide on the far side better. And there are certain Partitions I wouldn't use for shooting 500+ pound animals lengthways, if that seems necessary, but there some I would use for that purpose--and have, successfully, including the 200-grain .30 and the 250-grain .338.
You might also be interested to know that Phil Shoemaker tested a bunch of .30 caliber bullets for penetration a few years ago, and the the 220-grain Partition won. Dunno if any lost the front core, but based on experience doubt it mattered. You'll have to ask Phil, but he's busy right now, getting ready for the spring brown bear season.
“Montana seems to me to be what a small boy would think Texas is like from hearing Texans.” John Steinbeck
