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I use mostly Clays for my .40 loads, 3-4grs is all you need, so it makes a 1lb can go pretty far and it's very clean burning. Titegroup, as others have suggested is also a very good powder and burns clean. Some people have problems with inconsistent powder charges as the circular flake powders can be difficult to meter, so be careful.

Edit to clarify on the above a bit : .40cal is a high-pressure cartridge, when your using fast powders like Clays and TG you need to check your powder charge and double check. If 3.4grs is your max charge a small variance could cause a Kaboom if your not careful, especially in pistols that don't have a fully supported chamber.