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Posted: 12/6/2015 9:34:26 PM EDT
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ok guys during one of our local cmp matches i found out my rear sight was falling down under recoil. I have tightened everythng I have raised the rear sight all the way up and pushed down on it stays in place as it should but yet falls during recoil.....
any suggestions? or parts that may be worn and need replacement? i do have the flush nut type sight. |
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Well first I would suggest taking the sight off and inspecting the components;
elevation knob tit, is it worn down and rounded; if so replace the receiver ear with the radial serrations, are the grooves flattened where the knob engages; fix replacement serration disk glued over the top spring cover giving sufficient tension, if not replace You could also turn the tension screw inside the windage knob another click or two. I don't like them excessively tight as it adds to the wear on the tit on the elevation knob and the ear serrations. |
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If it's not gummed up inside (tear it down and hose it out with brake cleaner for starters), it's probably the sight cover or the elevation pinion. Reassemble it following the instructions for setting the tension correctly and see what you get (check the field manual under Regular Maintenance section). Most of the CMP rifles have pretty good serrations (assuming they're not gunked up) as GI's don't cycle the heck out of the elevation as a highpower shooter does. Sight covers are pretty cheap. I'd start there. Elevation pinion assy's are dicey IME, in several respects. I've found that a high percentage of them either have spring washers that don't meet the grade (causing the sight to lock up before it'll stay put) or they have a lot of lash in them so that 1 click up and 1 click down doesn't get you close to the starting point--something you can observe with your eye if you watch closely. The lash is something you can deal with if you know it's there (i.e. always go into a sight position from the down direction--so you may need to come up 2 and down 1 to get 1 up--this is probably a good practice in any case as they always seem to settle in the down direction). |
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I said I don't like the screw in the windage knob too tight. I will say guns that came from the CMP and that I know built up from parts have had that setting rather tight. One pretty consistent failing I saw on some CMP guns; the sight cover spring was worn out and those indented bars....on the underside were worn out. This more effects your windage as if you set things tight in the worn center, it will bind up when you hit the less worn sections of the indent. They're cheap enough to replace.
+1 to .30 cal's thought on adjusting to your setting only from one direction. I had forgotten about that old trick to deal with lash (sloppy fit). My gunsmith buddy has a heavy drill mill with some lash to it. He knows it's there and how to use it like .30 cal suggested so it's a non issue. |
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If its a flush nut sight you need to take it off and sell it to a collector . Prices start at $600
I would bet you have the T105 sight. "If" you actually have the screws properly tightened you more than likely have a worn tit/detent on the elevation pinion, its a common part that wears. The detent should be sharp. You can find used pinions with sharp detent around $35 |
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Quoted:
elevation knob tit, is it worn down and rounded; if so replace the receiver ear with the radial serrations, are the grooves flattened where the knob engages; fix replacement serration disk glued over the top If the serrations in the receiver are worn down under the elevation knob, loosen the screw in the center of the elevation knob, rotate the knob to a section of good serrations, and tighten the screw. True: your 200 yd zero won't show as "200" on the knob; but, you aren't shooting WWII GI Ball ammo anyway. Establish your zero and click up the correct amount from the bottom. |
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