It also limits lead exposure at minimal cost. Almost all airborne lead (something like 95 to 98%) is generate when the base of the bullet is vaporized by hot powder.
Are you sure that's correct? That directly contradicts what I've read about airborne lead contamination in indoor shooting ranges. I'm certainly no authority on it, but everything else I've read on the subject indicates the vast majority is due to primer lead compounds, and extremely little from metallic lead.
Also, the base of the bullet does not normally vaporize from the heat and/or pressure of the powder charge burning. The exposure time just isn't enough to do it.