Your right a Barnes fairly well just blows a hole through but a jacketed lead bullet as it frags sends bits everywhere, if you follow the little shoots of blood shot into the meat a lot of times you'll find little bits of lead or jacket that's why a guy should cut out meat till the dark streaks are gone. I used to shoot 100% Barnes bullets strictly because how good they are for meat but I prefer to put elk down dead and not looking for elk that should be dead!
Not one hell of an elk, but a decent sized 6 point. That's the total meat in the lug after boning the shoulders out. A good sized cow will run about 32 lbs of meat. I used to have all the numbers down but it's been a while since I was cutting a few hundred a year but those are good weight cause I double checked this week with a bull and couple cows. A good grinder goes a long ways to getting the yield a guy should, the Cabelas grinder is worth its weight in gold, it won't touch a 10hp 52 but it's dang good for the home guy, I timed it last night in case your interested my 1.5 hp Cabelas will coarse grind an average elk in 8 min and fine grind in 35min, that's 112 lbs of burger which is average.
An average small bull elk or a cow should be yielding you about 160 pounds of boneless trimmed meat for what you'd expect to pay a butcher to do it. An old 10 or 11 age bull almost 200 pounds. You can cut 15 more pounds off of this figure in intermuscle sheen, silver sheen, arteries, and other garbage that I trim out of my meat when I butcher it. I use the cabelas meat lugs, and filled nearly to the top they weigh 10 pounds each filled with trimmed meat ready for the grinder. I get between 2 and 3 (20 and 30 pounds) of trim meat (NO fat, silver sheen, tendon, muscle sheen, etc.) off of the front quarters of an elk (without the brisket, plate, and skirt) There is no butcher man in the world that will take the time to treat this meat the way that I can because it would be too time consuming. I also don't mess with the meat below the knee joint on any animal. It is just too sinewy, too hard on the grinder, and too terrible to eat after it is frozen. Every butcher man I know bones that out and throws it right into the burger or sausage pile.
So: Anybody that bones out below the knee joint will be getting about 8 more pounds of meat (sounds like what you're getting from your recollection).
The picture shown back a few posts ago is exactly what happens when you use a bullet that is not designed for bone to shoot through bone. All of that meat is garbage...I wouldn't soak or grind any of it, I would cut it out. It is full of bone and lead chunks. Also it is not a shoulder shot, it is a leg shot. I will say it again. HIGH on the animal is the shoulder. Specifically the shoulder blade where it meets the spine. No animal on earth takes a step after you shoot THROUGH that. Again, right at that spot you have the tip of a blade roast which is sinewy connective tissue, which is cut out anyway. You may bruise a few ounces of loin meat with a barnes, but I would say the over all meat wastage is less than 1 pound total with an instant kill.
I do stew meat and grind on all the front shoulder meat, some cuts of neck meat, meat between the ribs, brisket, and plate meat. After I finish stripping the silverskin off the meat with an ulu or fillet knife there aren't any steaks there. The rear quarter provides me with all the steaks & roasts, and about another 20 pounds of grind meat. I have an LEM 3/4 horse grinder which goes slow enough that I can stuff sausage casings with it, but goes fast enough to make quick work of an elk. I don't grind too much of the elk meat because its too delicious to just burger up.
All arguments aside meat loss or no meat loss....my method kills them instantly doing the best for the animal IMO.