What should I do with these? The bullet is sitting in a Thompson Center Mag Express .45-.50 sabot. I don't even know the grain weight.

shoot them. they look like they would be a lot of fun. Although if that is a .451 sabot, I bet they would make a good conical out of a White Rifle in .451.

Do you think that sabot will hold the bullet well enough to stabilize it?

My guess would be that's a 500 grain bullet. I suspect it will be pretty tough loading in that sabot, but all you can do is try. Another option would be the MMP orange sabots for .458 bullets.

i shoot 45-70 that are .459 and 405 grain and use 50 cal crushed rib harvester sabots with 150 grains of powder..alot of fun thru my black diamond xr....I like the thump

I'm having trouble finding a tight fitting sabot/bullet combination for my Knight Vision. I figure this combination should be pretty tight in the Vision.

I also have some 300 grain .45-70's in case these don't work.

looks like a 525 gr.
I shot them in my 45-70 over 65 Gr. 2F goex all I can say hope you don't were dentures they will rock you lights.

That's a big 10-4 there buddy!!! Good looking bullet.

From the picture that looks like a pretty heavy bullet.

You say it is a 45-70 bullet?? Just remember that the rifle 45 caliber bullets are .458 while the handgun 45 caliber averages .452. So the different bullets take different sabots for a firm hold on the bullet. Tom.