I was looking at some hardcast bullets on Gunbroker ,And was wondering: my 10mm Uzi will push a 155 grain fmj bullet at about 1500 fps.Can I push a 155 grain hardcast lead bullet at about the same velocity?.Most of the manufacturers dont even seem to know.Or should I just stick to JHP or fmj ammunittion?

With a properly sized bullet (.001-.002 over bore diameter) and with proper lube that should not be terribly hard.

Let's qualify the term 'hard-cast' however. This term applies to about any bullet that significantly improves on the hardness of soft lead. Elmer Keith was using 16:1 lead:tin, which has a BHN of about 12 when he developed his .44 special loads that lead to the 44 magnum.

I would recommend something a touch hard for your purpose. I would look to bullets in the 15-20 BHN range. 10lbs WW + 2.5 oz of Tin, dropped hot from the mold into water should work very nicely. They may even be a little on the hard side.

If you get leading, I would suspect the bullets are under-size, or perhaps too hard, before I would think too soft.

I have had great luck with 175 gr nominal weight (172 gr actual) in my Witness guns at all velocities. I don't water drop, and my alloy is about 11 BHN when air cooled.

Water dropped my alloy jumps way up (29-30 BHN according to my Lee BHN test). I am going to try some 220 grain bullets with gas checks in my 300 win mag one day very soon. Hope to get 2500-2600 FPS without leading.

I shoot 175 grain Lee tumble lubed hardcast out of my 10mm with minimal leading. Chronographed at 1275 - 1300 fps. It still leads a bit but accuracy hasn't been affected and I run a bore snake down it a few times every 50 rounds or so and it seems to clean it right up. As for hardness, I use straight wheel weights quenched in icy cold water with the cubes still floating. I could get harder by adding a little tin or some lino type but never felt it was necessary.

Jesse