hvacman,
I relieved the synthetic forearm on my .223 after it was fitted with a .357 barrel. The synthetic is pretty hard to sand or file, so I ended up using a air powered die grinder. A good bondo file (like they use on auto body work) might cut better while cutting a straight line.
I never did get enough relieved to get clearance for the .357, so I ended up with a 12 gauge shotgun forearm and had to relieve it some to get the .357 to float.