These are well made rugged picatinny/weaver style mounts that clamp to the barrel. Bottom section rests on the compression tube.
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I used a little Vortex Venom on mine for it's small size and light weight, Really any redot that will attach to a Weaver/pictnanny rail will work fine.
Give the Holosun line a look...after you buy a "barrel mount" rail, as shown above. Shorter ones are alo made. Just do some searching. Google is your friend.
I've got two Vortex red dots sights. Compared to the Holosun (and some other newer sights)...the Vortex EAT batterys !!! I just replace the batterys in both this past weekend. Have yet to replace any of my Holosun batterys. The Holosun sights get up to 50,000hrs worth of, on time !
What do you mean...retecal ? Your looking for a "dot"...sight...right ? The retecal is a..."dot" ! One hint, the smaller the dot the better. NOTHING over a 3mm dot. Red, green or even amber...your choice.