Tuesday, January 17, 2006

Adjustable scope mounts

by B.B. Pelletier

Yesterday, we talked about barrel droop and the fact that many airguns have it. Today, we're going to look at the solution: adjustable scope mounts. This is also the second part of an answer I'm giving to an anonymous reader who asked about an RWS C-mount.

Before we start, there have been one HECK of a lot of postings that deal with aligning airgun scopes. I've listed many of them so you can go back and read them, because the same questions seem to keep coming up. These are not all the scope postings - just the ones that deal with alignment issues.

March 2005
14 What causes scope shift?
18 How to shim a scope
24 Another cause of scope shift: over-adjusted scope knobs

June 2005
1 At what range should you zero your scope?
8 More about sighting-in: How to determine the two intersection points (scope-related)

July 2005
5 How to optically center a scope

October 2005
20 Why doesn't my gun shoot where the scope looks?

You may not need an adjustable mount
If your airgun shoots within acceptable limits and doesn't require a lot of adjustment to get on target, then you don't need an adjustable mount. Although I said yesterday that all firearms and airguns will be off as they come from the factory, many are not off by that much. This is especially true of the precharged pneumatics. The guns that seem to have the greatest problem with barrel misalignment are springers.

How to tell if you need an adjustable mount
When you have to do a lot of adjusting of either the windage or elevation knob to get the pellet to strike where you want it, you need an adjustable mount. On most scopes, the erector tube inside the scope tube is what moves the crosshairs. Opposite each adjustment knob is a coiled spring that pushes the erector tube against the adjustment knob. When the adjustment is run too far out (for example, too high for the vertical adjustment), this spring relaxes and doesn't put much tension on the erector tube. Consequently, the tube can bounce around and perhaps move to a new setting on its own accord. This is especially true on guns with heavy recoil and those with a lot of vibration. To prevent this from happening, a set of adjustable scope mounts can be installed. The scope can then be returned to the center of its adjustment range, and all necessary windage and elevation adjustments will be provided by the scope mount.

RWS C-mount
Ten years ago, there were a lot more adjustable scope mounts than there are today. Nobody had tested them to see how they worked. When writers started reporting on how adjustable mounts worked, many of them fell by the wayside because they actually damaged the scope! The RWS C-mount was one of these. The C-mount (a one-piece mount that looked like the letter "C") adjusted for elevation only. Although the rings went up and down independently at the front and rear, they didn't compensate for tilt when they weren't level. If a rigid scope tube is suddenly elevated by its rear ring and still held firmly by the front ring, the tube has to bend to accommodate the elevation difference between front and rear. The RWS C-mount was bending scope tubes!

B-Square to the rescue!
B-Square has long had an interest in airguns. The founder, Dan Bechtel, saw the problem adjustable mounts were causing and went to work on a solution. His solution was the B-Square adjustable scope mount. Not only do the rings adjust up and down independent of each other, they also tilt backward and forward, as needed, to compensate for the misalignment. When they're adjusted, they put no strain on the scope tube! They also adjust side to side.

There were several European adjustable mounts that sold for hundreds of dollars and still bent the scope tube. B-Square just about put them all out of business with their new mount. To my knowledge, only one other manufacturer made an adjustable mount that didn't bend the tube - Sportsmatch. Theirs was a one-piece mount, which proved too limiting for the American market.

I note that Gamo now has an adjustable mount. I've never examined one; from the picture, I see that it's also a one-piece and only adjusts for elevation. From the look of it, it would not strain the scope tube when adjusted. It looks simpler than the B-square rings, so if elevation is your only concern, perhaps this is a good mount for you.

Remember, you don't need an adjustable mount if you can get on target with just small adjustments of your scope. But, when you have to make large adjustments, it's time to start thinking about adjustable scope rings.

21 Comments:

At January 17, 2006 2:57 PM, Blogger Bob said...

On a gun with barrel droop I would think that when you sight in the scope it would only be for that specific distance that you sighted it in for. Since the barrel is on one plane and the scope is on another, the scope would only be correct for that one specific distance. If the distance is closer or further I would think you would need to re-sight the scope.

 
At January 17, 2006 3:35 PM, Anonymous MCA said...

Just a bit off the subject - apparently the TX200 ships with no open sights. Is it at least drilled for mounting sights? Which sights would fit it?
Thanks

 
At January 17, 2006 8:49 PM, Anonymous Anonymous said...

Bob,

Any gun is only ever sighted in for one specific distance, doesn't matter whether its a drooper or not.

Depending on your choice of zero distance, you may find the pellet's trajectory intersects the scope's point of aim a second time, or perhaps even approximates it over a range of distances. The key word here is of course 'approximate'.

Graham

 
At January 17, 2006 9:19 PM, Anonymous Anonymous said...

BB,


I accidently shot my gamo cf-x with the rotary breech open and some smoke came out.I dont know if thats too bad.What can happen if the breech is left open?

Thanks


CF-X guy

 
At January 18, 2006 10:41 AM, Anonymous JB said...

CF-X Guy,

I have accidentally dry fired my cf-x a couple times, never with the breech open though. I was distracted and just forgot to load a pellet. I was worried about damaging the piston seal, but performance in my gun was not affected. GAMO's web site has a FAQ section that says their rifles can be dry fired! That is contrary to what most spring gun shooters believe, many seals have reportedly been ruined by dry firing. The puff of smoke is caused by a small amount of lubricant in the gun being burned. Commonly known as "dieseling". BB has spoken of this in previous posts. I don't think you hurt your gun.

BB, how about a post on dry firing and such with springers and different types of air guns?? Dry firing is a great practice technique, but we don't want to ruin our shooters! Thanks.

JB

 
At January 18, 2006 10:54 AM, Anonymous B.B. Pelletier said...

JB,

That sounds like an excellent topic. And CF-X guy, I have spoken to Juan Carlos Casas, one of the owners of Gamo, and he told me the conpany tests the ruggedness of their guns by dry-firing a test gun 10,000 times, then stripping ir down to see whether there has been damage. Through this program, Gamo has learned to make their guns more rugged.

Oh, Oh! I'm writing the column, aren't I?

B.B.

 
At January 19, 2006 8:19 PM, Anonymous Anonymous said...

Thanks BB and JB for the info.One more thing BB,

What can I do to know if my cf-x is really 1000 fps as advertised since I dont have the thing to messuere speeds.Thanks BB.

CF-X guy

 
At January 19, 2006 8:22 PM, Anonymous B.B. Pelletier said...

CF-X guy,

I wish there was an easy answer for you, but that's why chronographs were invented. You can always check relative penetration ((one gun against another - same pellet), but for an absolute speed you need a chronograph.

B.B.

 
At January 20, 2006 6:02 PM, Anonymous Anonymous said...

BB,

Thanks for the info ill save some money after I get the leapers 12x44 scope!!!

CF-X guy

 
At January 21, 2006 2:52 PM, Anonymous Anonymous said...

CFX Guy,

Don't forget rings! Leapers' scopes are 30mm and BSA's are 1". ( a point I overlooked last year )

dsw

 
At January 21, 2006 8:55 PM, Anonymous Anonymous said...

dsw,

Thanks for the info.You and BB have helped me a lot!!!.Here is my email so you send me a picture of your cf-x with the leapers scope.Im sure its great.hernan_classic@yahoo.com


CF-X guy

 
At January 23, 2006 7:00 PM, Anonymous Anonymous said...

dsw,

WOW!!!!!!!!!!!!!!!!!!!!.I have to get that scope.The pics are great.Love you cf-x.One question.If I buy the scope do I have to take the open sights off or could I just put the scope more to the back.

Thanks

CF-X guy

 
At June 22, 2006 10:56 AM, Anonymous Gamo Owner said...

B.B.,

I mounted a one piece B-Ring adjustable scope on my shadow 1000 yesterday but after 4-5 shots it seems to wobble within the rings? The only way I can get it to stay put after it starts to wobble is tighten the windage screws but that throws off any adjustments I previously made. Is there somthing I am missing? What do you reccomend I do?

Thanks,
Gamo Owner

 
At June 22, 2006 5:22 PM, Anonymous B.B. Pelletier said...

Gamo Owner,

If you are talking about B-Square adjustable rings, the problem is probably that the sideways adjustment screws are not all tight. It just takes one of the four to be loose to do what you describe.

Now make sure you tighten the SIDE screws and NOT the locking screws that only lock the side adjustment screws.

Once those screws are tight you can chin yourself on your scope and it won't get loose (but don't try it!).

B.B.

 
At April 12, 2009 2:55 PM, Anonymous Keith_J said...

RWS C-mount, when properly installed, will not bend the scope.

First, clean the threads and pinch points on the mount. Install the base to the rifle, then install the rings on the scope without tightening the base to the rings. Just use the base to align the rings.

Now elevation can be adjusted on the C-Mount by loosening the base to ring mounting. Slight wingage adjustments can be made in the ring to base mechanism.

I have found applying rosin to the pinch points on the ring bottoms makes the mount hold much better with magnum recoiling guns like my RWS 48.

 
At July 07, 2009 6:51 AM, Anonymous Anonymous said...

I was looking into an affordable alternative to getting a Unertl type scope for a cartridge fire gun and was wondering if the one piece B Square adjustable mount can handle being put on a firearm, specifically a .308 BLR. Thanks

Tom

 
At July 07, 2009 8:07 AM, Blogger B.B. Pelletier said...

Tom,

You will need a B-Square mount made for a firearm. That would be one with a Weaver base.

I think I would stick with steel mounts on recoiling firearms.

B.B.

 
At July 07, 2009 10:33 PM, Anonymous Anonymous said...

Okay, the search continues... Thanks

 
At December 05, 2009 1:35 PM, Anonymous Anonymous said...

Re. adjustable scope mounts: Darned if I see any adjustment screws or whatever on the B-Square rings your site linked to. I can see that they might swivel independently, but no screws for up/down, L/R! Wrong photo? http://www.pyramydair.com/s/a/B_Square_10101_1_Interlock_Adjustable_Rings_11mm_Dovetail/235

(The Gamo mounts are discontinued: http://www.pyramydair.com/s/a/Gamo_1_Pc_Adjustable_Mount_w_1_Rings_3_8_11mm_Dovetails/599 ) but at least an elevation knob shows.


Randy H

 
At December 05, 2009 2:18 PM, Blogger kevin said...

Randy H,

The Pyramyd Air picture doesn't show the adjustment screws but they are there on the back side.

The Pyramyd Air description is also lacking. These do adjust for windage and elevation. Throw the intructions away when you get them and pay very close attention to B.B.'s instructions when adjusting these mounts. They're tricky. DO NOT OVERTIGHTEN THE TINY ADJUSTMENT SCREWS OR YOU'RE SCREWED.

keivn

 
At December 05, 2009 2:24 PM, Blogger kevin said...

Randy H,

Thought your comment was under the b square adjustable mount tutorial that B.B. did but this isn't it.

Here's a link to the 3 part series he did. Parts 1 & 2 can be accessed by clicking on them at the top. Here it is:


http://www.pyramydair.com/blog/2007/07/b-square-adjustable-scope-mounts-part-2_05.html

kevin

 
At December 05, 2009 4:20 PM, Blogger B.B. Pelletier said...

Randy,

Those are indeed adjustable mounts and they do move in both directions. The entire ring screws up and down on a large central post.

The horizontal screws are on the sides of the rings., but they are in an underhung position and don't show here. The tiny screws Kevin refers to are the locking screws.

B.B.

 

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