Fireforming .44-77 brass?

[Distant Thunder]

With my new .44-77 project nearing delivery I have been wondering what would be a good way to fireform the brass I have waiting.

I don't plan to load anything until I have the rifle in hand, but I'd like to have a plan in place once I do.

Since this rifle will have the standard Shiloh grease groove chamber a lot of options are open to me I'm sure, but what have the rest of you done for fireforming your new brass in the cartridge?

I have 300 cases to fireform. I would rather not burn through 3 1/2 lbs. of my good black powder and match quality bullets to get this done. If I'm thinking wrong on this let me know.

If this was just a .45 caliber straight case I would not worry about it at all. I'd just buy some inexpensive bullets, use enough powder to get the job done and use as generous a wad stack if needed. This being a bottleneck case may require a different approach, I don't know but likely.

I could cast a bunch of lighter paper patch bullets and load them as deep as possible in the case to reduce the powder and lead used.

I have a few hundred grease groove bullets left over from years ago and just sitting around since cast. I could lube those up and seat them deep, which I'd have to do with this long shank bullet. I don't think ant kind of filler is useable here, or is it? COW?

I also have some miscellaneous powders that are really sort of orphaned and not used in any of my match loads. Odds and ends of leftover lots or powders that didn't work out for match loads. That is probably the best choice powder wise so I can conserve my good stock for match shooting.

Is there a source for reasonably priced .44 caliber bullets either PP or GG that I could use for fireforming?

So have you .44-77 shooter done for fireforming? Thanks!