Okay
, since you changed the springs and it didn't help the next logical culprit is the gas system.
1.) Gas-Cylinder Lockscrew.
A.) Stupid question but, is the screw on tight and the threads Clean?
Yes, and yes.
B.) Is the valve damaged or cracked?
This is a subject that has me confused. The gas cylinder screw seems to be a solid plug with no valve, orifice, etc.
2.) Gas-Cylinder.
A.) is the Gas-Cylinder cracked at the screw?
The gas cylinder is mechanically sound.
B.) Is it oversized, take an empty Remington 7mm magnum case and stick it in after cleaning the Gas-Cylinder, base-first(Secret!!!! The belt on a Rem.7mm mag. measures .530). Now,look in the other end of the Gas-Cylinder where the Op-Rod enters, can you see light around the case? If so, you need another gas-cylinder.
I'm able to insert the case up to .50" of the shoulder. Looking at a bright light bulb in this condition shows slight light leakage around less than half of the belt.
3.) Op-Rod Piston.
A.) It should measure no less than .5256" with a 0-1" Micrometer.
In most places, it measures between .5245" and .5255" with my standard RCBS caliper. I don't own a micrometer. The replacement op rod 
sent me measured the same as the one that came with the M1, and I told him what the original one measured......which annoys me somewhat.
B.) Are any of the rim-edges chipped?
There aren't any chips.
C.) If you answered yes to either query, you need a new piston, Call Columbus Machine, they'll install a new one very reasonably.
4.) Barrel port.
A.) Clean out the cruddy carbon with a toothpick and mike it with a #47 drillbit, should enter the port.
A #47 bit goes in, but not with finger pressure only......light persuasion is required.
B.) Try again with a #45 drillbit. This is the No-Go gauge for the port. If this bit fits the port is too big, only answer is another barrel.
A #46 won't fit, so it's definitely not too big.
Good luck and let me know what you find, maybe I can help.
Dave
So from this it seems that the gas port is on the small end of the acceptable range, the op rod piston is too small, and the gas cylinder is at least acceptable.
I can easily ship the op rod to Columbus machine to have a new piston installed.
Thanks for your help with this.