Hi, I used the Lee lead hardness tester to test the eBay scrap lead recently received. Both sources of lead had a test result of ~8 Brinell hardness. That test shows the lead to be pure. There is a fingernail test to see if lead is soft. If your fingernail can dent the lead it is probably soft. Of course using a lead tester is the only reliably method to test lead hardness.
People talk of using reclaimed range lead and wheel weights. Some of that lead can be pretty hard. Loading hard lead balls using the loading lever of the revolver can sometimes cause the loading lever to break. Muzzle loaders used with a patch could care less what the hardness of the ball for target shooting. However, trying to force a hard lead projectile in a revolver chamber can be difficult. Also, most BP revolvers have cylinders that have chambers of smaller diameter than the bore dimensions. Soft lead will upset to fill the bore rifling on firing, hard lead will not. Something to consider in selecting lead for casting projectiles.
Regards,
Richard