The old loads still work because IMR4895 hasn't changed significantly in all that time. Your op-rod needs to be in good shape.
Note that the Hornady manual loads are way milder than the old loads. I haven't had a chance to talk to their techs about it, but I believe they are falsely premised on the idea a medium load will get you lower gas cylinder pressure than a maximum load. In reality, powders with burn rates appropriate to the Garand will have the gas cylinder pressure peak in the middle range somewhere, about where Hornady's load maximums are. Above that, bullet velocity gain with additional charge starts to outpace muzzle pressure rise. As a result, the time between when the bullet exposes the gas port to the bore pressure and when it exits the muzzle gets shorter faster than pressure is growing. The result is it can't pressurize the gas port as much before the bore pressure drops to near zero.
The main thing is just to find a load that shoots as accurately as your Garand can take advantage of it. 168 and 175 grain bullets with IMR4895 in the 47 grain range, plus or minus a grain, often do well. With 150's, figure 48.5 or so will be close.
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