"so after I while I figure to tighten the screw that's on the elevation knob"
Your'e tightening the wrong screw. The screw on the elevation knob on both the Garand and M1A (basically same sight) is so that once you are sighted in, you can loosen this screw and index the sight so that you can set known distance range settings by lining up the proper yardage on the elevation knob.
There is a wave spring washer inside the elevation knob which holds the elevation detent tension so rear sight cannot slip down.
Proper adjustment on rear sight tension is set as follows:
1) Run rear sight all the way up.
2) Try to push down with your thumb on top of rear apperature.
3) If you can push down, increase tension on the wave spring by tightening the
spanner nut in the windage knob. This nut can be tightened with a special screw driver ground with a slot in center to clear the end of elevation spindle.
Note: There is a special lock built into this adjusting nut that requires it to be tightened in 1/2 turn increments. You will feel it drop into the "groove" when you reach the proper spot.
Tighten 1/2 turn and try it until you can no longer push down the rear sight with your thumb.
A word of caution, do not tighten more than necessary as it makes your windage knob harder to turn, the more pressure you put on the nut.
If, you have difficulty adjusting windage when elevation tension is properly set (this sometimes happens), you can make windage changes easier by pushing in on the screw in center of elevation knob with one thumb while turning the windage knob w/other hand.
"SA sent me another NM frontsight and it sights in 20 or 21 clicks up."
This is not good. It makes your rear sight much too high for proper cheek pressure at long range (600 yds). To help this, you can carefully file the top of the new front sight off so that your 200 yard zero is somewhere between 5-8 clicks up from the bottom. If you ever shoot your rifle at 100 yards, DO NOT go below 5 clicks @ 200 (if 200 is where your are sighting in) or you will be unable to get low enough for 100 yds. There is usually 3 clicks difference in the M1/M1A between 100 and 200 yards.
Rough rule of thumb, IIRC is that .003" = 1/4 minute but don't trust my memory all that much, take your file to the range and cut 'n shoot.
Do not use locktite on your sight.
Regards,
hps