I have no first hand experience with loading the .348 Winchster - however:

Wolf Publishing "Big Bore Rifles and Cartridges" has an excellent article page 70-74 by Dave Scovill on cast (& jacketed) shooting in the .348 Winchester M71.
This is probably a repeat of a Handloader magazine article.

Scovill's loads hold to 200 and 250gr. bullets.
Scovill's cast loads with RCBS and LBT bullets made 5 shot groups averaging an inch or less at 100 yards using 27gr. H4198. The RCBS bullet of 200gr. was doing 1,721fps while the LBT 250gr. was running 1,672fps. He also experimented filing the case with grex with some of the 4198 loads. His other cat loads were with H4895 to 43.0gr. and H4831 to 63.0gr. Velocities ran to almost 2,200fps with H4895 and just over 2,000fps with H4831..

John Kronfield takes the next 4 1/2 pages to do an article on the .348 Ackley Improved with both jacekted and cast.

Kronfield's data also lists cast loads with 200 and 250's along with 300gr. Hoch bullet.