Been shooting the RCBS 200s for several decades in a few 35s. Found the 200 FN plain base double (discontinued by RCBS) powder coated, nose down, then sized to groove diameter using a case lube pad, works fine, without a gas check to 2,500 fps with no leading. They shoot sub 1/2" in a 12-20 twist barrel, as I have a 12, 14, 16 and a 20. In the small capacity cases I use H-110, medium capacity 1680 and large capacity, like the 35 Whelen 4350. But with the 350 L the straight case should load like the 357 Super Mag rifle, (Max) of which I have two.
To try the 180 RCBS I recut the AR feed ramps which was a bust because the 180s were about 1/2 as accurate as the 200s.
SAECO still makes the iron dual cavity RCBS 200 plain base moulds.They are the best for powder coating for accuracy and feeding that I have found for auto and bolt feeding. Just finishing a 358 Win cast bullet bolt gun for them. On a Mauser action.
The left is my 358 MGP for a AR-15 with a PCed 200 RCBS plain base. That does 2,491 fps with 1680 over my chronograph and shoots .43 inches at 100 meters. I do not worry about expansion. As the 200 hard cast is like a freight train, goes right out the off side, taking the lungs and heart with it.
Next is the new 358 Win