I finally got to take my new CMP garand out shooting, and to my suprise, my very first group at 100 yards was dead on centered on the bullseye, about a 6 inch group. As I shot more, however, my groups moved, and I noticed the elevation on my rear sight had changed. My question is, how tight should the elevation screw be? I have the WWII type rear sight, not the lock-bar type. TIA for any information.

Edited to add the 100 yard zero, that I shot the first group with, was bottomed out +10 clicks (there is a line on the elevation knob there, just below the 200 yard line). As I shot, the elevation increased, and when i noticed it maybe 24 shots later, it had moved up to the 800 yard setting. Thanks.

You should tighten the screw until it will no longer allow the elevation knob to turn, then back the screw out one click.  

If your still having problems, then the tension washer may need to be replaced.

Done.
It'll be a few weeks til I can make it out shooting again, I'll test it out then. Thanks.

Quoted: The Lock Bar sight is the WW2 vintage, you have the post-WW2 rear sight.

He could have flush nut sights.

My rear sights look like the ones called Flush Nut sights on page 8 of "The M1 Garand Owner's Guide" by Scott Duff. Im taking it out next weekend for more serious shooting, I'll let everyone know how it does.

Ignore this post, I just upped my member status and am playing with all the profile settings

Quoted: My rear sights look like the ones called Flush Nut sights on page 8 of "The M1 Garand Owner's Guide" by Scott Duff. Im taking it out next weekend for more serious shooting, I'll let everyone know how it does.

What's the left side look like?  Does it have the large screw slot in the middle or is it small?  Is the pinion short or long pinion?  If you have flush nut sights, those could be worth several hundred dollars to collectors.  Also, what kind of rifle do you have?

The rifle is a rebuilt mutt, and I dont have it in front of me, but I'm pretty sure the sights are HRA.