Well, I know one fact is this. A steady diet of 190's in a stock Garand will ruin the op rod.
No maybe. It's a fact.
That's because in it's standard configuration it is not set up for a steady diet of 190 grain bullets. There are ways to work around that. Schuster and McCann plugs are one way, easily obtained and not expensive at about $35. I know guys who are running 208 AMAXs and IMR4350 with the right mods. Which is those 35 dollar plugs.
A Garand's gas system is designed around the M1 and M2 loads, more specifically the M2. If you get away from those loads in powder burn rate or bullet weight (150 to 175 grain), you will bend the op-rod.
Tune the system to the load and you'll be good to go.
Heavy bullets play havoc with a standard Garand gas system due to the time under the pressure curve as much as total pressure due to the lower velocity, giving the system time to take on more volume of gas and continue to accelerate even if the burn rate of the powder is correct. This can lead to battering and bending from continued use due to the reciprocating parts moving too fast. The heel of the receiver can become another area that fails, too.
Increasing the volumetric capacity of your system(GarandGear), or bleeding the excess off(McCann or Shuster), will allow you to eliminate or significantly reduce any problems you may have. Keep the reciprocating speed near design parameters and your parts will last.
I use the GarandGear plug in mine.
I haven't built a whole lot of Garands, and the ones I have only have been in .30-06 and .308. But looking at the ejection pattern, I'd say that particular gas system is pretty well engineered correctly.
