Hunterdave I do not know about the 300 grain and I can not speak for the terminal performance of the the bullet, but the 250 grain with 120 grains of Blackhorn 209 are supper accurate out of my T/C Prohunter. I just got back in to Muzzleloaders this year and am looking fwd to the coming season. Also some of the 250grains I shot were shot into a thick archery target we call the Blob. It is dense and very tough we were able to remove one of the bullets that went all the way through and into an old stump. Expansion looks good. Did not check the weight retention but this is proably the load I will be using around here for deer this year.