Lead vs Jacketed

[Joey]

I have been casting and reloading for a number of years. With that said I have a very studid question that I just thought of.

Why is there a difference between powder and amount with jacketed and lead. Such as 160 gr. Jacketed bullet vs 160 gr. lead?

I know this is a stupid question and I am almost embarressed to ask.:confused:

[pumpguy]

Lead boolits seal the barrell better. With j word bullets, you get more blowby.

[dubber123]

Lead is generally alot more slippery than copper, and takes alot less to force it down a bore, not to mention it is almost always lubed, whereas jacketed bullets generally aren't. Less friction=more speed with less powder. In handguns at least, I have always been able to get much more velocity at safe pressures with cast than with jacketed.