I've replaced the springs in my Garand including the op rod spring with a Wolf spring kit as well as adding an adjustable gas plug.
I have the plug adjusted almost all the way open now "maybe 2 increments left" and I'm getting occasional miss feeds with ammo that used to run flawlessly. The load is an 149gr  M-80 bullet and 47gr IMR 4895.
I know I'll have to increase this load or go back to the original op rod spring till I use up the ammo I have on hand.
My question is, is it safe to use heavier loads comparable to what I might shoot from my bolt guns if I can tune the Garand down to the point where it ejects cases like standard military ammo normally would from a non modified Garand?

if it was a + power spring, get rid of it for a standard weight one, Ive seen more problems brought about on guns because of people screwing w/ things like springs to 'improve' them and they just make 'em run unreliable

The extra power op-rod springs will foul up the Garand operation. Standard rate springs work very well unless you need a heavier clip latch spring. (for enbloc clips jumping out while firing the rifle)

Buy the new op-rod springs from Orion7. They are top notch in quality and have improved several of my rifles. I routinely replace the old op-rod springs in all my CMP with the Orion7 spring. Read up on their website on how they are made, good stuff for the Garand

Bottom of the page, $8.00 each
http://www.m1garandrifle.com/news.htm

+1  Orion7 for your springs, nuff said.

agree with sig- ain't broke don't fix it- I've been messing with m-1's since the early 1980's and never felt the need for aftermarket parts or adjustable gas plugs!!!

I did have problems with it starting last winter shooting in cold weather 30's "not real cold" but wouldn't fire on 1st couple tries or if left to get cool off after firing.  So I figured an extra power hammer spring was in order and replaced that as well as the other springs while I was at it. I also had a couple slam fires this spring after replacing the springs so I added the adjustable gas plug to regulate the speed of the op rod. I'll likely change out the op rod spring for the one listed previously for $8.00 and buy their Shop manual for the M1.
There's no such thing as too much knowledge I suppose, but too little can be dangerous.
Thanks for the info!

Slam fires were probably from the extra power op-rod spring. The firing pin is not spring loaded and closing the bolt extra fast can get the firing pin to kiss the primer too hard- Bang!
The cold weather shooting, maybe too much grease or oil on the action? When things get really cold, it can gum up the works. I think the military used to remove all the oil/grease for really cold weather to keep it running.

Keep shooting that fine rifle