I have tried reduced velocity, cast lead loads for both 30/30 and .308. My succesful 30/30 load was for a Marlin 336, bullet was a 155 grain lead flat point with 9.5 grains Unique. It shot to the same point of aim as factory 150 grain, full power loads at 50 yards and was fairly accurate. Unfortunately, I no longer have that rifle.
My best luck was with loading cast lead was for a .308 Ishapore bolt action rifle. The same 155 grain bullet with 9.5 grains Unique made a super accurate load, five rounds touching each other at 50 yards, dead on to point of aim. This load also shot to the same point of aim at 50 yards as surplus 150 grain FMJ ammo. Believe it or not, I don't own that rifle any more either, forum member Muley Gil has it along with all of my accurate cast lead rounds!
So, I now own a Winchester "Ranger" 30/30 that I am working up a cast lead load for. I wanted to duplicate the performance of my past rifles, find a mild, cast lead load that will hit the same POI/POA as 150 grain factory ammo. First tried a 165 grain cast lead bullet with 8.0 grains Trail Boss, point of impact was too low at 50 yards, like 4" below point of aim. Just recently bought some 135 grain cast lead bullets, loaded them with 6.5 grains Trail Boss, point of impact even lower, like 8" below point of aim. So, it looks like this rifle wants a heavier bullet to hit to point of aim, so I'll try to find some 180 grain cast lead bullets.
I tried Unique pwder with this rifle and couldn't find an accurate combination, very poor accuracy. The Trail Boss loads give good accuracy, like 1.5 inches at 50 yards, just low POI.
I guess if you just wanted to shoot cast lead only, you could find an accurate load and adjust the sights on the rifle for that load, but I want the flexibility of shooting both factory 150 grain cartridges and cast lead handloads, so the experiment continues...
For those who doubt the utility of a 30 caliber cast lead bullet, I found them to be very effective against varmints out to 50 yards, a 155 grain cast lead bullet at 1000 FPS will drop a fox or nutria in it's tracks, only quieter than a factory round while doing it. I also thought them to be much safer while shooting in marshes, as they will only travel so far, like a shotgun slug. You can shoot them without hearing protection, ladies and kids love shooting them, plus they are fun to experiment with!