Scope shimming

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GoldenStateAIRGUNer

GoldenStateAIRGUNer

Member
Dec 2, 2018
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Ca, United States
I just mounted a scope on a newly acquired FWB 124. I drew a vertical line and a dot (aim point) and started shooting at about 8 ft. Did not want to miss my 4X4 and put a ventilation hole in my sliding glass door. The first shots in the 8-13 ft range were all right of center. Moved back further and now all shots are left of center. I even had a little lower hits than at the 8 ft distance. That would indicate some barrel droop. In order to keep shots on the same vertical plain at 8 ft to infinite it appears I need to shim the scope. My logic tells me the recticle end of the scope needs to go to the shooters right. The objective end of the scope needs to go left. Am I right in my thinking? Here is a picture of my testing.

20201202_150334.1606951348.jpg

 
Bubble level may help.
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Isn't a scope level kind of subjective to whether the rifle is perfectly level ? What's the best way to consider the rifle level ? The top of the breech block (break barrel) is one way but the receiver may not be on the same level plane as the barrel breech block. What about across the top of the scope bases as shown in the picture diagram? Those are some aluminum can .005" shims I made.

20201202_192922.1606966444.jpg

 
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Dovetails should be perfectly level especially since it's made in Germany old school style. I do not recommend shimming and scopes on any guns but that's just me and especially on springers. 

I would use droop compensating mounts already machined into the 1 piece mount for Springers or Burris Signature XTR and offset shim inserts with 11-13 mm scope dovetail rail adapters with scope stop pin. 
 
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Dovetails should be perfectly level especially since it's made in Germany old school style. I do not recommend shimming and scopes on any guns but that's just me and especially on springers. 

I would use droop compensating mounts already machined into the 1 piece mount for Springers or Burris Signature XTR and offset shim inserts with 11-13 mm scope dovetail rail adapters with scope stop pin.
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I know shimming can be bad if to much is used. Don't want to collapse the soft scope tube. I will probably just use one (.005) and not more than two (.010) shims. I've read other info that one to two at max is OK. I will probably just shim the rear to eliminate the droop error. As far as left and right cant errors I will look more into it. I just read the entire piece on cant that Michael posted. I'll explore some of those ideas mentioned.
 
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From the canting piece.

" Mirror method:
I stand a mirror down range so that I can look through the scope and see the scope objective and the end of the bore in the mirror. I then rotate the scope in the mounts until the CROSSHAIR IN THE SCOPE intersects the center of the bell housing and the bore at the same time. That gets me in the ball park. On low, one piece mounts, the bottom of the turret housing can sometimes interfere with the mount before the scope can be rotated enough. On at least one of my rifles, I just live with the minor cant error that remains. The better way might be to machine some additional clearance into the mount."

So by "croshair in the scope" he's referring to the vertical hair ? Lining up the cross with the center of the objective bell and then rotating the scope until the vertical crosshair lines up with the bore? Am I reading that correctly? 
 
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Another thing I'm going to do is zero out both the windage and elevation of the scope and start at close range and see where my shots go. I also watched a YouTube video about scope adjustments. Its not advised to go anymore than 75% of your scopes adjustment range. Let's say your elevation adjustment has a total of (just a example) 200 clicks. That means 100 clicks would have the elevation set to zero. Three quarters of that is 150 clicks. That means you should go no more than 50 clicks in either ( up or down) direction. This has to do with the spring tension on the erector tube within the scope. The erector tube springs need to be under tension in order for the scope to hold setting. If you run out of adjustment in any direction the spring is not under tension as much. That's why people experience issues with POI shift when they run a adjustment to much in one direction. I'll check my Sig Sauer Whiskey3 scope today and set it to zero.
 
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GoldenState

With break barrel rifles, it's not uncommon to have barrel droop. If you don't want to use a droop compensating mount, you can adjust the rifle by barrel bending. There are multiple posts on different methods to do this. I personally think this works great, and with patients and a lot of nerve, you can adjust your barrel to be spot on. Then use your "centered" scope with little or no adjustment, and no shims. 
 
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GoldenState

With break barrel rifles, it's not uncommon to have barrel droop. If you don't want to use a droop compensating mount, you can adjust the rifle by barrel bending. There are multiple posts on different methods to do this. I personally think this works great, and with patients and a lot of nerve, you can adjust your barrel to be spot on. Then use your "centered" scope with little or no adjustment, and no shims.
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Only issue I see with barrel bending is making sure it's 100% bent in a vertical plane. Don't want a left or right cant to the barrel
 
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I wrapped my barrel with a wide peice of leather and put it into a vise up side down shimmed with wooden blocks. Not too hard to line it up so that you pull the stock in the right plane. You can correct droop fairly easily using stock for leverage. Mechanicaly zero scope first and lock into desired position. Bend barrel a little with scope on, remove and test fire for results. Repeat until you sneek up on ZERO. Don't over correct if you can help it, harder to go the other way.

I locked the barrel into the vise about 3 or 4 inches from the breech to give an early correction, but left enough room to actually bend it. 
 
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I wrapped my barrel with a wide peice of leather and put it into a vise up side down shimmed with wooden blocks. Not too hard to line it up so that you pull the stock in the right plane. You can correct droop fairly easily using stock for leverage. Mechanicaly zero scope first and lock into desired position. Bend barrel a little with scope on, remove and test fire for results. Repeat until you sneek up on ZERO. Don't over correct if you can help it, harder to go the other way.

I locked the barrel into the vise about 3 or 4 inches from the breech to give an early correction, but left enough room to actually bend it.
Click to expand...

That's a last resort ! And I mean very last ! I'll get it squared away with mount changes.
 
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