I know there is a gauge for the muzzle but do not know how to measure throat erosion. I do not have the tools for either measurement. I have two Garands to check out. Thanks for your consideration!
I have the gauges. I live 5 miles north of Whiting Field, Milton. Matter of fact, I did a throat measurement for Plinker's AR15 this morning. Met him at his range on the way to Pncla Rifle and Pistol Club where I shoot.
Most accuracy problems in my experience with the garand have to do with loose bedding and at times modifications to the gas system. I would suggest paying attention to the condition of the muzzle crown an bedding. I assume you want to measure the throat and muzzle due to poor accuracy. There use to be an NRA publication on some of the simple things one can do to accurize the M1.