If one would make an effort to find out what an alloy does fired with real black powder and there is a difference between powders used on how the bullet obdurates with different alloy hardness. When a bullet leaves the muzzle looking good it will shoot good if the one sending it down range does.
The first two the left one was fired and the unfired one is the same unfired. The bullet is a 715 grain .50 cal. creedmoor nosed from a Paul Jones mould. The fired bullet has completely changed in profile and it was cast soft with 1/40 L/T and it shows signs of stripping and it shortened .097" in length.
The 9 are all the same shot with different alloy hardnesses. The first is unfired.
A GG hard alloyed bullet at groove diameter with a good wad under it will hold the gas back just fine because it's a tight fit on the bore.
The Hollow point rebated hollow based bullet is one I worked with a few years back to see how a rebated boat tailed PP will perform over a flat base normally used. That bullet is a mix of 1/16 lead, tin, 5% antimony and patched to bore diameter and it filled the grooves very well. The problem with this profile design was protecting the base from damage.
The alloy temper is a shooters choice, what ever he is satisfied with the results.
For me 1/16 L/T or 1/18 L/T/Antimony is my choice. I only shoot the PP bullets.