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Lyman Sight Problem on AO 28AC


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When firing the gun, with the sight down, the sight will not stay at zero, but the entire sight slides up the sight leaf so the sight is now at 600. What do I tighten down to stop this? Or is there some other solution to stop this.

 

Thanks

 

Jerry

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Actually, that is a quite common phenomenon on the Lyman sights on the Thompson in full-auto fire. You could start with the sight on the 600-yard position if it annoys you. It doesn't affect the use of the sight in the upright position, so it shouldn't be a huge problem unless you really like using the small notch on the leaf sight while it is at zero.

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Without seeing your sight, my guess is either a defective, loose or missing slide catch. On the left side of the slide you will see the slide catch and the screw that retains it to the slide. The catch is a small rectangular flat spring with an imbedded pin that projects against the serrations of the ladder providing the necessary tension to keep the slide in place.

 

If the screw is loose or the catch (flat spring) has lost tension (or it’s pin is worn or missing), the slide is then free to move along the ladder.

 

If everything looks complete, a simple test is to move the slide along the ladder. You should hear distinct 'clicks' as the catch pin rides against the ladder serrations.

 

Previously, I've seen sights that were reblued without disassembly and the heat from the bluing process caused the catch to lose it's tension. The slide would then freely move along the ladder. The solution was a replacement catch. At the time, Gun Parts Corp. had them in stock; not sure if they or anyone else has them available today.

 

Another possibility is that the ladder serrations are extremely worn but it would take an awful lot of use for that to occur.

 

Hope this helps.

 

Paul

 

Lyman Sight.jpg

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