Hope you are well and greetings from Northern NV!
I don't know if you remember but I shoot both a 50/70 roller and a '86 in 50/100/450 both with a 480 grain bullet. Starline makes brass for both!! I have never loaded smokeless in either one and never will. That being said If I was to load smokeless I would shy away from the 50/110 and lean towards the 50/70 with its shorter case. I'm sure you could develop all the horse power you wanted with the 50/70 without the danger of double charging the larger case. If your nephew ends up going home through northern NV have him get a hold of me and he can try them both out!! I have a couple of other larger guns in the smokeless variety that have a pretty good kick to them that he could try as well.