Blank Firing Adaptor (BFA) hole size, in a good serviceable Garand (all parts gauge, good springs, properly lubricated, ...and all other things are right with the world) should be around 0.195"-0.200" for use with the new Army Issue Ceremonial Crimped Blanks.
For well worn rifles, 0.175" is a good starting point. If the rifle always loads the second round, but never the third, continue opening up the hole in the BFA until all 8 rounds fire flawlessly, and they will with the issue crimped ceremonial blanks. We just finished repairing two more police department honor guard rifles they thought would never work, and have done a lot of the VFW & American Legion guns as well. They now run like the proverbial Singer® sewing machine!
Be certain the gas cylinder lock screw (gas plug) is not missing the valve. We recommend the Fulton Armory solid screws/plugs, as well as a heavy duty clip latch spring.
We also recommend, when everything is running right, to LockTite® the BFA and gas plug in place with red 271 for "blank only guns" and blue 242 for mixed use, and, to be certain to tighten the gas plug tightly against the BFA, thereby forming a "compressed shoulder."
Hope this helps.