Since we are engaged in a bit of topic drift anyway. What is the advantage of the tube sight over separate front and rear sits?

The top picture is the Anchutz 18MM Apreture Clamp Ring that I use for the Acrylic inserts that takee the M18X.5 Tap and cost only $10.00. Below it is but one of several 18MM adjustable types mine goes from 2.0 to 4.0 and by stating several I am referring to the various choices such as the cross bar shown, or crosshairs or on and on and price is very dependent on choice of Gehmann, Centra, Anchutz, Others and Apreture design. They all use the same M18X.5 thread design as do the Diopters, Sunshades and various other 18MM accessories. I might add they will all also screw into the front of the Anchutz clamp but not the various adjustable types and thus the clamp is by far the better choice for my own use. With the adjustable's you also have be careful it is not one of those used at the back of a sight as you can then see the back side of the adjustable iris and it might not appear to be round.

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JLouis

Ratseye I can only hope that something I might have shared has been somehow helpful for you. In all honesty when tapping the M18X.5 hole it has to bored very accuratly to spec. If a bit under or over due to the threads being so fine and shallow it really cannot be accomplished correctly and you end up with no threads or wiping them out while trying to tap and it really is that critical. With that being said and if possibly not having that capability I would very seriously take a real close look at Jerry H's approach and I am sure he would be more than happy to explain his entire process and what he uses on the front if so being required. One would be hard pressed to find a more willing individual who enjoys helping others and his approach would indeed be a high quality one.

JLouis

My error and miss-understanding Ratseye my having permanent partial eye sight loss from a stroke back in 2011 I thought I was on the same page as you. I was thinking about what it was I had to do for myself to continue shooting the Iron Sight matches and should have been paying closer attention to what exactly what your own needs are.

JLouis

I said I would report when I finally shot the gun with the new peep sight. Today was it and I am more than happy. I know that this isn't much in the world of real competition shooters but I was at the point of selling my iron sighted guns because of not being able to see well enough. 

The rifle is a Martini Cadet in 32-20 WCF with an excellent bore. The load is IMR-4227 in Starline brass and a CCI-LR primer, using a bullet cast from a custom CBE 130 grain heeled bullet mold with my home made lube. That bullet is quite accurate in another Cadet of .310 caliber. This was before my vision started to really nose dive. So shooting this same load that the BEST I could do before in the 32-20 was a 7" shotgun spread, today's best was 1-1/4" for five at fifty yards. THAT my friends is a significant improvement and made me a believer. I think I can do better as I work on the adjustments but being able to see the front sight clearly and the target almost as well made a huge difference. It may not work for everyone but it sure helped me. Thanks for all your input, ratseye

There are 2 mentalities in people, fixed & growth.  Fixed people think there is nothing they can do to change their condition, growth types, like Ratseye, study & learn how to respond. We can all learn from this.

I always believed that every problem has a solution if you never give up. I can attest to hundreds of ways to not do something before finding the answer. I am humbled by the level of knowledge and the willingness to share that this group has shown me. It is much appreciated. ratseye

Unfortunately that is not how mine worked with my Gehmann rear apreture and I am not sure just why? Had I known I would have gladly sent you mine before purchasing yours to use on a test piece. Other than coming from China who supposedly had the correct Metric size and the only one I could find. All though the outside of the container was correctly marked in MM but not what was inside and noted as being the same. It worked out very well for me so I am completely baffled to why?