A problem inherent in Tanker Garands is the lack of engineering behind the conversion. The op-rod was designed to function with a 24" barrel. When the barrel is shortened, the op-rod cannot be correspondingly shortened and expected to function as on the normal gun. First, because of a shorter barrel, the closer proximity of the gas port causes the gas to act faster on the op-rod. This means unlocking happens faster. Second, pressure drops quicker since the gas is expelled faster from a shorter barrel. Third, besides the gas affecting the op-rod sooner, the lightened op-rod moves faster than the normal op-rod (all these combine to make the action faster in terms of unlocking, extracting, ejecting and reloading). Fourth, the helix cut in the op-rod that engages the bolt lug and controls the movement of the bolt was engineered for a certain unlocking time. Perhaps most important are the angles engineered into the op-rod by John Garand. They were not intended for faster operations and therein lies the crux of the problem. Mere shortening of the rod does not ensure that the gun will function or if it does function, with the same life span of a normal size gun.
Beretta addressed the issue on their shortened BM-59 by engineering a new rod that was somewhat straighter than longer M-1 Garand op-rod. Beretta may have engineered other changes (smaller gas port, different recoil spring strength, modifying the helix cut), but not having one available for examination, I am unsure about it.