Try one of Anthony Pucci's new stainless steel springs at orien 7 www.m1garand.com
"Extra Power" replacements may not work well at all.
Try lotsa grease on the bolt. When was the last time you cleaned out the gas system and made sure the gas cylinder plug was tight?
Have you greased the operating rod under the barrel?
If you remove the op rod spring and tilt the gun up and down...does the op rod slide freely?
I'd also post your problem on the M1 Board of jouster.com for the real Garand-Nutz.
1943 CMP Springfield Service Grade, 1943 Springfield Barrel, SA/ GAW stock. A legite WW-II Veteran
I've shot crates of the Greek Ammo...it's fine. But do you get the same problem with other ammo too? You've got a gas-system/spring problem imho. "Heavier Weight" springs may not be the solution.