[LouBoyd]

The problem is that there are few firearms other than those specifically made for shooting subsonics which will do a good job.

The problems are:
1. Too much case capacity to give good velocity uniformity.
2. Too long of twist rates to stabilze long heavy bullets.
3. Too short of magazine or barrel throat to allow long bullets.
4. may clog gas ports when shooting unjacketed lead.

Most bolt action rifles suffer from 1 and 3.
Most semi auto rifles suffer form 1, 3, and 4
Most pistols suffer from 2, and 3

Heavy cast lead works fine in a 300 whiper bolt action just fine. You can shoot cast lead in a 308 too but it won't give great performance because of the excess case capacity. Several methods have been discussed on this site about ways to reduce case capacity.

Where I see the advantage of cast lead is shooting heavy bullets in large bore rifles with long barrels. Cast lead doesn't need hollow points. It expands well with just a round nose Also heavy large bore bullets have decent BCs just because of their mass to sectional area despite the fact they aren't very aerodynamic. I shoot lubricated 525 grain Postell style cast bullets seated deeply in my 45-70 Browning BCPR with fast bulky powder which give both subsonic bullet and propellent velocity at the muzzle. It's quiet enough that hearing protection isn't needed with muzzle pressure well under 1000 psi.