Hello from a fellow owner of said caliber. I am not sure that I am the one to answer your question. I am a beginner at both handloading/cast bullets. One thing I am good at though....asking more questions! Here are a few things that have danced through my cranium...fellas correct me if I'm wrong:
Most load data for the 356 seems to only go up to 250 grains(Speer lists to only 220 but M.L. McPherson's lists for 250's). This has always suprised me as the 356 in a 20 inch tube only lags behind the 358 by a small margin(using Flat Pointed Bullets). Most of this difference is accounted for by a 2" shorter barrel. I haven't seen any loads for heavier than 250 granis in 356 Win., though perhaps there is for it's close cousin the 358 Winchester or some other manual lists them. As you probably know, you can't interchange info between the two as the internal case dimensions are different.
These rifles have short(or non-existant?) throats. A heavier bullet of the LFN design...that is greater than 250 may begin to extend below the case neck? Apparently, this is a cast bullet no-no, as the bullet maybe be deformed. I am not sure if a gas check changes this equation. Also, in relation to the above, might the short throat begin to give you problems in terms of the bullet beginning to press too heavily into the rifling in these heavier, and longer bullets? On another note, I think the short throat on these guns may be a positive thing in that you may get more consistant results from slower burning powders with 200-250 grainers. This is just from what I've read, but not real world experience. I have had good luck with the slow burning IMR 4350, but this is a low velocity load. I would like to try IMR 4320 for increased velocity, but have to put money into my piggy bank for a bit more.
I think a 200-250 grain bullet would be plenty enough for what you want to do. I want to use cast in hunting also, and I want to make sure that I get expansion that provides a quick kill. Annealing sounds promising(running a butane torch over bullet noses in order to soften them). There was once an article on the BTB site which describes this. I would like to hear from fellows who might have used annealed bullets if you come across this post. Just a few things that went through my head at your question, which is a good one. Wish I could be of more help.
A forum community dedicated to Sport shooters, owners and enthusiasts. Come join the discussion about optics, hand casting bullets, hunting, gunsmithing, styles, reviews, accessories, classifieds, and more!