Apart from the legal aspects,why would you want to turn a Cadillac into a Trabant or something equally inferior? Yes,they have been dicked with to produce a so-called "tanker carbine" with a shortened barrel,but muzzle blast and functioning are always an issue here.They can be re-barreled to another cartridge with a .30-06 size casehead.incl .243,.25-06,.270,8mm-06 and .35 Whelan,but this requires the use of an adjustable gas plug for correct functioning.The easiest conversion is to .308 Win by simply replacing the barrel. Garands can be made to be extremely accurate in both the standard .30-06 or .308 Win calibers by tweaking the fit of various components,glass bedding,or the use of a heavier barrel.The sky is the limit as far as cost and time are concerned.My own accuracy expectation from a properly set up M1 with a sound barrel in as-issue condition is 2" groups with handloads @ 100 yds.But if one wants to spend the time and money to produce a match grade rifle,you can pretty much be assured of MOA accuracy with quality handloads.