Gentlemen,
I bought a Marlin M94 in 357 magnum last week. Unfortunately I bought it sight-unseen through a friend.
This friend of mine didn't see the "Microgroove" stamped on the barrel, so I wound up with my first MG Marlin in about 30 years.
I once had a M336 in 44 Magnum and it wouldn't shoot cast bullets at all until in desperation I loaded the Lyman 429244 unsized. My mold casts this design at 0.434 and I loaded them as-cast. Loaded cartridges looked like a snake swallowing an egg but they did chamber and accuracy was outstanding.
Now, with this new 357 I skipped all the load work-up, went right to my oversize NEI 150-358-PB which casts bullets of 0.363, lubed them only in the 0.364 die, loaded them over Bullseye into unsized cases and went to the range for testing. Again, the MG rifling gave me outstanding accuracy with the massively oversize bullets.
All a fellow need do it seems is load big bullets for the Microgroove barrels. However, always make sure the cartridges so loaded will fit the gun's chamber before you load more than one!
Good afternoon,
Forrest