John Garand himself did some conversions and found that it wasn't as straightforward as it seems.
For one thing, the desired purpose was twofold: selective fire and secondly, common BAR magazine used so as to simplify logistics. Well, the BAR mag didn't feed reliably since the M1 Bolt was too fast. The spring would have to be changed (then it wouldn't be reliable with the BAR) or the M1 Garand receiver lengthened 1/4" so as to give the bolt more space to travel - hence more travel time. Remington Engineers resolved this problem by putting in a inertia rod in the op-rod to slow it down. This worked, but by that time, interest had passed. Too bad it wasn't semi-auto only.
But, as Jim said, rapid fire is the easiest way to promote barrel wear and none of us here (Gale McMillan excepted) is into replacing barrels on a regular basis.
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