More Shimming

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1BadDart

1BadDart

Member
May 15, 2017
1,038
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Kentucky, United States
As I had mentioned in a previous post that my Diana 48 killed it's Konus Pro 8.5-25 scope so I replaced it with a Mueller 8-32 with a mil dot reticle. The base is a UTG drooper with six screw Burris 30mm rings. After mounting the new scope I didn't have enough elevation, so through my flawed reasoning I ordered a new mount with no droop. WRONG! I needed more droop compensation, should've done more research lol.

The UTG rail is approximately .040" shorter in the front than the rear and the 1" RWS dropper that I ordered with the rifle is about .025" shorter in the front than the rear so there was no use in ordering a RWS 30mm mount. After finding nothing that would work I decided to shim my UTG mount. I have stainless shim stock but was afraid it would mar the aluminum rail and the dovetail on the rifle so I cut some pieces of aluminum can. The can is .0037" so I folded it (.0074") and added it under the rail on top of the rifles dove tail. I only had time to finish and shoot a few rounds right before dark and at 12 yards with the elevation ran all the way out the rifle shoots about 3/4" high. I'm in the process of building a transmission for the hot rod but may take a few minutes to shoot it at 25 yards and see where it shoots. Hopefully it won't need anymore shim.

I have some targets for the ten dime challenge printed and am looking forward to see how bad I can muck it up. lol
 
Depending on how much you're willing to spend to solve this problem...you could always mount a DIP25moa slope 11mm dovetail to Picatinny adapter (http://www.diproductsinc.com/Detail.aspx?PROD=175301), which will give you 25MOA of starting inclination and will then give you a Picatinny interface, allowing you to use one of several 1-piece AR mounts that will provide additional inclination. For example, American Defense, Bobro, Aadland, and a couple other brands all offer units with between 10MOA to 50MOA slope built-in, which when added to the 25MOA you already have, gives you anywhere between 35 - 75MOA of compensation that you won't have to use in scope elevation adjustment. The only downside is these 1-pc AR mounts can get pretty expensive. But mechanically, this approach is way superior to shimming, as too much shimming really puts your scope in a bind. 
 
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That will work too. The reasons I prefer the DIP adapter I linked over the UTG drooper adapter is first of all, the DIP adapter is Picatinny spec, and the UTG is Weaver. Though they share the same width and overall design on the rail portion, Picatinny mounts have wider cross pins and won't fit on many Weaver bases without enlarging the slots, though the opposite (Weaver based rings on Picatinny rails) will work every time. You can certainly enlarge the slots as needed, but I prefer not to have to do that. Since there are tons of good rings for Pic rails and few Weaver rings that I think are worth a crap, I will opt for the former whenever possible. Secondly, the DIP adapter is much lower profile. Otherwise, I do prefer the fact the UTG adapter doesn't have an ejection port cutout (the DIP adapter is designed specifically for CZ rimfire rifles, though will work on an airgun 11mm dovetail) and has more ring spacing flexibility.

On the last point, when you put a shim between the rail and the top of the receiver, you're creating uneven dovetail engagement, as the dovetail tries to pull the mount down. The end with the shim will thus not have full engagement and the adapter rail clamp will not get full line contact along the dovetail. This can also bow the base slightly as it tries to seat unevenly onto the dovetail as one end cannot fully seat with the shim underneath, which would cause rings mounted onto the base to be slightly misaligned as a result.
 
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