I did fail to mention the reason I use the Ported Gas Plug. There are two bad things that can happen with a Garand when you use improper ammo. One is a “Kaboom” where you have a bolt or chamber failure. Keeping it to The CMP’s recommendation will prevent that. The other thing that can happen is that you can bend your op-rod. This can happen when the barrel pressure at the gas port exceeds the design limits of the M1. While a give cartridge may have a max pressure at or below the SAMMI standard of 50,000 CUP, the pressure at the gas port may be higher than what the op-rod can handle due to the particular burn characteristics of the propellant used. This can lead to a bent op-rod if the op-rod is binding for any reason (often lack of proper lubrication). Garand Gear has a good article on the M1 and its ammunition:
M1 Garand Ammunition and the Ported Gas Plug that talks about this.
If you check out the article, you’ll see most commercial grade ammo with a bullet of 150 gr will have a port pressure above that of HXP-69, a standard M1 round, though most will be below LC-66, another standard round. The 180 gr loads will all substantial exceed HXP-69 and LC-66 (even though they meet the SAMMI standard). You will also note that even HXP-69 and LC-66 exceed the reference round loaded with 50.0 gr of IMR4895, which is the standard load called out in the M1’s Army tech manual. If the port pressure is high and the op-rod binds for any reason, you have a good chance of bending the op-rod
The Ported Gas Plug significantly reduces the pressure that the op-rod is exposed to, but not to the point of impairing performance (as long as you have a non-binding op-rod as demonstrated by the the
tilt test).