Does anybody know if it makes a difference forming .30 Herrett and .357 Herrett cases with 30-30 Rem. brass vs. 30-30 Win. brass?

Just use all the same. Actually, no difference. In .30 Herrett I've made brass from an assortment of cases. I've seen experiments that have caused the experimenters to reach contradictory conclusions (to one another), but see no reason to be unduly worried about it.

My question is, how did you come to have this question? Me thinks there is much left unsaid.

Actaully, not a whole lot to hide. I just purchased a bulk of brass that was Winchester flavor and I keep all my reloading consistent. Always had access to Rem. brass - but the price was too good to pass up on the Win. Tried .375 brass once, this just did not agree with the barrel during fire-forming.

Wasn't implying that you were hiding anything only that some things were ommitted. Often what is left unsaid is as important as what is said.

Logically, there will be differences in brass. You say that the .375 Win brass didn't agree with the barrel. Some people have used .225 Win brass for these cartridges in order to get a thicker neck. I think that forming from the .375 would do the same. Whatever you meant by "agree with", I think that you'll probably be happier with the .30-30 brass. I don't see differences in velocity or groups even when firing groups using mixed brass.

One thing that did not work for me is the use of 110 gr. bullets in the .30 Herrett.

However, again, I wonder why you ask if you already have the brass.

By "not agreeing w/ the barrel during fire-forming" I mean like salt mixed w/ iced tea. Some people like, some don't. I had major case weight differences after fire forming the .375's. Out of 85 cases that started within +/- .2 grains, I was lucky to have 20 that were that close.(I weight my prepped cases to determine capacity consistency).The .30-30 cases seemed to retain a more consistent weight. Why ask the question after I purchased the brass? That's a fair question. I do not base my research on others results, however will learn from others findings. Make any sense? In other words, I'm going to form, reload, and accurize (is that a word?) a load using these shells period.If you would have posted a thread saying that you tried the same thing and it didn't work - shortened case life, fractures, etc. - I could keep a look out for the same things and maybe not try certain aspects of my reloading process. Uncommon man shooting an uncommon gun. I do appreciate your posts!