Which side is which?

[GatorCountry]

Which side of a reversible 3/8" and 11mm dovetail ring mount is which?  The side with the larger extension or the shorter?

I'd think the longer extension would be for 3/8" since it is 0.375mm (vs 1mm at 0.433) to seat into the slightly narrower groove spacing.  However, trying to fit a new set of UTG rings on a TX200 I'm not yet satisfied with the seating using either orientation.  So...decided to go back to basics but couldn't find any markings on the rings or prior posts on GTA that (re)started me on solid ground.

Suggestions or insights welcomed.

[GatorCountry]

To add some clarity on what is seen as the problem...either orientation of the clamp bar on the rings provided a definite cant to the naked eye, then proven with two bubble levels (known good and in sync).  The pictures below illustrate a virtually identical cant with each. 

Each was mounted very deliberately and held in place by hand to insure good grip and angle maintained in the dovetail while tightening.  Maybe my other dovetail mounts have always been like this and I'm being extra picky with this setup.  Thinking I may need to walk away from this for a while and come back to it for a fresh perspective.

[Roadworthy]

I've never checked for cant, offset, or level.  When using either / or rings I remove the plate from the mount.  I then check to see which side fits best into the dovetail groove.  That is the side I leave down to ensure solid clamping action.

A 3/8" dovetail and an 11 mm dovetail, although pretty close in distance, are machined at different angles.  One is cut at 45 degrees and the other is sixty.  I don't remember which is which.  There are mounts made to center perfectly straight and level but they're more expensive than the either / or type.

[GatorCountry]

...check to see which side fits best into the dovetail groove.

Effectively what I decided to do in order to complete the job tonight - chose the best available and decided that had to be correct - or at least optimal given the choices.  Especially after I took a one piece dovetail mount and mounted it with similar results.

Interesting point on the angles.  They're definitely different angles and lengths on each side of the mounting bracket.  The one piece mount appeared to be 45 on both, so guessing it was not made to be reversible.  Unfortunately I don't know it's stated width or would use it as the reference for the other.  I did find an article by Tom Gaylord that effectively confirmed that confusion on dovetail mounts is normal:

https://www.pyramydair.com/blog/2007/03/11mm-scope-dovetails-why-do-they-interchange-with-38/

Thanks for the response.  It helped checked my sanity (on this one issue) for tonight.

[nervoustrigger]

An 11mm dovetail has a 60° angle. 

A 3/8" dovetail has a 45° angle.

[nervoustrigger]

By the way, it does not really matter if you get it "wrong" when attaching a scope, provided you align the reticle with the muzzle and hold the gun such that the reticle is plumb/level.

[GatorCountry]

By the way, it does not really matter if you get it "wrong" when attaching a scope, provided you align the reticle with the muzzle and hold the gun such that the reticle is plumb/level.

That is how the final assembly was setup.  It makes sense that any of the 360 degrees around the muzzle are theoretically just fine for the optic, as long as they're both in alignment.  Have the two vertical planes slightly offset - the one through the reticle and the other perpendicular through the action and the stock - is what didn't seem right.  The reticle was aligned when the rifle was shouldered naturally versus leveled in a rest, so it "feels" correct shooting offhand.

Good identification info on the clamping bar angles too.  Added that to my running air gun note file.  Thanks.

[GatorCountry]

Related to just the cant of the mounts themselves, Leapers responded to my question, earlier today with the following:

... your [TX200] receiver is a rounded profile dovetail. This is preventing your rings from obtaining the proper purchase on the rail. The product that would work around the rounded dovetail would be MNT-DTW145.

That product is a dovetail to picatinny rail adapter.  It does have a rounded profile under the rail, but adds height and switches the ring setup. 

Edit:  The combination of scope cant and gun cant matches scenario "F" in the chart produced by Scotchmo referenced in several posts, such as https://www.gatewaytoairguns.org/GTA/index.php?topic=128123.msg1260667#msg1260667   Based on that went ahead and ordered the Leapers recommended mount.  Already have a 30mm set of picatinny medium rings.  Should bring it back closer to center over the bore, then will remove any remaining cant via the mirror method described.