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How much can I lap my rings ?
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<blockquote data-quote="Hugnot" data-source="post: 2591540" data-attributes="member: 115658"><p>The FN Browning may be 65 years old. Exterior dimensions were not carefully controlled - pre CNC days ^^ ("action that is not perfectly machined and drilled"). Varying exterior dimesions rifle to rifle were common, like .005 or more. Screw holes may be slighly misalinged. One piece, 3 hole, ring turn in bases were common.</p><p></p><p>Mounting 2 piece bases having uniform dimensons on a receiver having variations on height of bridge & ring, along with misalinged screw holes (like 4) is certain to create scope mounting problems. $176 rings (throwing $ at problem) will not fix this. </p><p></p><p>Ring lapping will promote uniform contact between scope & inner ring surface but won't fix problems caused by failure to have axis of both rings common. The fix is to shim or bed mount bases. The best remedy would be to epoxy bed both bases using something like JB Steel Weld.</p><p></p><p>My suggestion is to buy appropriate cross slot Warne bases and Burris Signature Zee rings and shim as required. The front Warne base may be had with an extension for mounting short scopes. </p><p></p><p>[ATTACH]384697[/ATTACH]</p><p></p><p>Here is a FN Mauser, very similar to the OP's. Same vintage give or take 3-4 years, same manufacturer, FN, about 55 years old. Observe the Burris 1 inch Signature Zee rings and Warne rear & extension front bases. Upon placing my Wheeler alignment bars in both rings with "0" inserts a noticable drop in the rear ring and left side inclination was noticed. The rear base was elevated .007 with a shim cut from a Miller Lite beer can. The left inclination was fixed by using a + 5 insert on the left side of the front ring. The scope reticle was centered by centering the reticle with its reflection in a mirror. Additional insert adjusting resulted in an otimum (best possible under restrictive conditions) scope installation without dial adjusting. No bending of scope tube, or receiver flexing. </p><p></p><p>No amount of lapping would fix the misalingment problem but would increase surface contact between scope & rings by grinding down high inner ring surfaces.</p><p></p><p></p><p></p><p></p><p>Any electrolytic corrosion between the steel base & aluminum shim (not much EMF between both) should be prevented by an application of blue grade thread locker between shim & steel. Checking out shims that have been used near salt water for many years shows no corrosion on either surface. If in doubt, steel shim material can be had at Brownell's. The aluminum shims have not been squashed by mount screw tension.</p></blockquote><p></p>
[QUOTE="Hugnot, post: 2591540, member: 115658"] The FN Browning may be 65 years old. Exterior dimensions were not carefully controlled - pre CNC days ^^ ("action that is not perfectly machined and drilled"). Varying exterior dimesions rifle to rifle were common, like .005 or more. Screw holes may be slighly misalinged. One piece, 3 hole, ring turn in bases were common. Mounting 2 piece bases having uniform dimensons on a receiver having variations on height of bridge & ring, along with misalinged screw holes (like 4) is certain to create scope mounting problems. $176 rings (throwing $ at problem) will not fix this. Ring lapping will promote uniform contact between scope & inner ring surface but won't fix problems caused by failure to have axis of both rings common. The fix is to shim or bed mount bases. The best remedy would be to epoxy bed both bases using something like JB Steel Weld. My suggestion is to buy appropriate cross slot Warne bases and Burris Signature Zee rings and shim as required. The front Warne base may be had with an extension for mounting short scopes. [ATTACH]384697[/ATTACH] Here is a FN Mauser, very similar to the OP's. Same vintage give or take 3-4 years, same manufacturer, FN, about 55 years old. Observe the Burris 1 inch Signature Zee rings and Warne rear & extension front bases. Upon placing my Wheeler alignment bars in both rings with "0" inserts a noticable drop in the rear ring and left side inclination was noticed. The rear base was elevated .007 with a shim cut from a Miller Lite beer can. The left inclination was fixed by using a + 5 insert on the left side of the front ring. The scope reticle was centered by centering the reticle with its reflection in a mirror. Additional insert adjusting resulted in an otimum (best possible under restrictive conditions) scope installation without dial adjusting. No bending of scope tube, or receiver flexing. No amount of lapping would fix the misalingment problem but would increase surface contact between scope & rings by grinding down high inner ring surfaces. Any electrolytic corrosion between the steel base & aluminum shim (not much EMF between both) should be prevented by an application of blue grade thread locker between shim & steel. Checking out shims that have been used near salt water for many years shows no corrosion on either surface. If in doubt, steel shim material can be had at Brownell's. The aluminum shims have not been squashed by mount screw tension. [/QUOTE]
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