I built, from the ground up, my M1 Carbine, M1 Garand and M1A. After installing the barrels on the Carbine and Garand the receiver and barrel head spaced just fine. However the M1A was to tight and would not close on a "GO" gauge. The gunsmith at Buckhorns had to order in a reamer specifically to do the job and he cut the chamber perfectly. The bolt would close on a "GO" gauge and moved approximately .002" on a "NO GO". It don't get much better than that.
I was never charged for the reamer or any part of it, which makes sense as he will surely use it on other rifles, but still, it was a very good experience. I think he charged me around $75 to.
I highly recommend him.