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Thread: Scope ring lapping - how to

  1. #1
    Member bgreen's Avatar
    Join Date
    Oct 2006

    Default Scope ring lapping - how to

    I've been having some trouble with my Sako .243 so I decided to lap my rings before I send the Leupold back to the factory.

    I used a piece of 1" 6061-T6 Aluminum, but cast iron would have been better. I'd use mild steel or 4140 if that was all that was available. You can get very good 1" material from your local industrial steel shop, or maybe even an industrial machine shop in your area. Ask for 1" pump shafting, or TGP. It should measure within .0005" and be more than straight enough for this application. Measure it with a good and zeroed mic to be sure, BEFORE you buy. For a handle I drilled and tapped a 3/8-16 hole, threaded in a piece of all thread, and threaded on a handle off an old cheap screwdriver. If I build another lap, I will braze or solder a ball bearing onto the end of a bolt for a more ergonomic handle.

    I've never lapped rings before, but I wasn't expecting what I found...

    This picture is after lapping for a few minutes with JB bore compound.

    Notice how uneven the contact is!

    I wasn't getting quick enough results from the JB so I switched to some old valve grinding compound I had out in the shop.

    The valve lapping compound worked much better, but took considerably more effort. Careful adjustment of the ring screws made things easier, but I didn't want them so loose I would loose alignment.

    Notice the contact area spreading out now?

    Any comments, questions, suggestions?
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  2. #2
    Join Date
    Feb 2007
    Eagle River

    Default Lapping


    Your experience was similar to mine. I lapped the mounts on my Ruger M77 with the Brownell’s lapping tool and noticed that the lapping marks were very heavy on the circumference of the leading edge of the Ruger mounts. My reason for lapping is to insure the scope doesn’t get into a bind. I wasn’t sure how far to go with the lapping, so I followed the directions I received from Brownell’s and went until I had a good 50% contact pattern. I found that valve grinding compound works well.


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