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  #1  
Old 07-28-2018, 12:07 AM
JDMANN

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Front Aperture Diameter



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Would anyone know the diameter of the front aperture of the CM-2 rifle?
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Old 07-28-2018, 03:03 AM
tim slater is online now

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Hard to say, as these are interchangeable, and a selection was supplied. It could be anywhere between 3.0mm and 4.0mm. The diameter of the aperture is usually marked on the insert/element.

The aperture needs to be large enough to contain the aiming mark, and leave a broad enough gap for reliable aim; the inner edge is fuzzy rather than a clean step, and one can overlap ring and target if the gap (when the target is centred) is very thin.

It's likely the elements are sized for the International 50 metre target, with its 4.5in aiming mark. That's about 8 Moa. Typically one would use a larger aperture for Standing than for Prone as the aim is less steady. However factory supplies elements tend to be on the small side.

If you mean the diameter of the whole insert, that's about 15-16mm.
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Old 07-28-2018, 11:13 PM
JDMANN

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I'm sorry I wasn't clear. I meant the outside diameter of the whole aperture. Thanks for the info. 15-16mm appears about right.
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Old 07-29-2018, 03:25 AM
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Quote:
Originally Posted by JDMANN View Post
I'm sorry I wasn't clear. I meant the outside diameter of the whole aperture. Thanks for the info. 15-16mm appears about right.
It's called an insert or element. The aperture is just the hole in the middle, which do come in a variety of sizes.
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Old 07-30-2018, 12:15 AM
JDMANN

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Ok, tjm slater. Thanks for the correction. Can you answer my question on the "insert" or "element" size?
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Old 07-30-2018, 02:39 AM
tim slater is online now

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Originally Posted by JDMANN View Post
Ok, tjm slater. Thanks for the correction. Can you answer my question on the "insert" or "element" size?
I thought already had, but a quick Google search produced this thread: https://www.rimfirecentral.com/forum...d.php?t=234440

O/d was measured at 14.71mm, so the threads would be a nominal 15-16mm. There was a caveat that the factory changed the o/d at various times. It's somewhat smaller than the standard 18mm (actual 17mm o/d) " elements, but similar to the later Parker-Hale. Redfield sights are almost non-existent here in the UK, so I'm not sure how these would compare.

Last edited by tim slater; 07-30-2018 at 02:42 AM.
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Old 07-30-2018, 02:30 PM
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As Tim mentioned, apparently there are a few different diameters out there. I recently acquired a newer Izhmash/EAA CM2 Youth model, and it accepted the inserts I had from my Anschutz -- they are 17mm outer diameter, with a 15mm 'shoulder'.

Based on those positive results, I ordered a set of Champion's Choice inserts (the $28 10pc set), expecting them to fit right in.

UNFORTUNATELY, the Champ's Choice inserts are 17.20mm diameter, and lack the shoulder/step in the diameter. I made a little fixture and machined the diameters down on a lathe last weekend, and I think they are going to work okay. I'm not the best machinist, so I didn't hit the diameters perfectly, but they shouldn't move once installed. Worst case is that the zero won't be repeatable when I switch them out, but I can live with that.

marky-d
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Old 07-30-2018, 05:28 PM
bilco40k

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MY Mu12-2 fore sight has a outside diameter of 15mm with offset locating lugs and a 1.2mm recess. Pity your not in the U.k. as i have a set I made with 1,2,3,4mm holes.

If you know some one with a laser engraver i have a coreldraw file with the Mu12-2 fore sights I could send you.
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Old 08-03-2018, 08:12 PM
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