The gas cylinder lock screw (aka "gas plug") keeps the gas cylinder lock from unscrewing. On some rifles, this is just finger tight so it is possible it could unscrew a turn or two during firing.
Also, the gas isn't intended to go forward, so the threads are going to get fouled in short order. Lots of fun to clean before you put the lock screw back in.
I've read of some shooters buying a spare part and drilling a hole in it to make a gas cylinder lock screw that essentially disables the Garand's action. This should cause no harm, and the dummy screw will protect the threads.
is there an automatic adjusting gas plug?
Not that I'm aware of. The closest thing would be to get the McCann style plug and set up a drilled and tapped plate to carry in one of the holes in the stock. If you number the holes and keep track of which threaded insert provides the correct function for each ammo type, it is relatively easy to swap inserts when you change ammo.
But you still have to use a trial and error method, starting with the largest orifice and working smaller, to determine which to use for each ammo type.
And, I believe that even the largest orifice will not handle "light magnum" type .30-06 ammo.
