[Unclenick]

Sounds like it isn't locking up completely. Try one of the Wolf extra-power op-rod springs. Keep the op-rod bolt lug cutout lightly greased.

If it doubled it is likely the second round in the string was a slamfire. You want to check that the safety bridge in the receiver isn't bent. Check the lengths of your bolt and firing pin.

If the round that slam-fired was a handload, it was probably not the gun dimensions but a high primer. Check that your primers are below flush with casheads always. About 0.004" below flush is ideal. The primer seater built into the Forster Co-ax press is perfect for Garand ammo because it forces that condition to be true. You can also use CCI #34 military hardness spec primers for added insurance.