It speaks of a horrendously-abused rifle.
If the gas-port pressure is correct, the energy of the properly-pressurized gas is consumed in compressing the op-rod spring and in loading the next round.
If the gas-port pressure is too high, the op-rod/bolt assembly is essentially a miniature pile-driver pounding on the back of the receiver.
The rifle action overall is exceptionally strong.
The common description of the original Garand proof-testing is along the lines of:
Mr. Garand built up progressively higher proof loads in increments of 5,000 lbs. pressure, from the regular proof load of 70,000 lbs. to the extreme figure of 120,000 lbs. per square inch. At this later figure, cracked left lugs on the bolt began to be encountered. A gun in which the bolt had the left lug cracked by one of these excessive high pressure overloads was then fired an endurance test of 5,000 rounds of service ammunition, using the cracked bolt, which showed no further deterioration.