Scope Mounting Experiment

IHMSA80x80

New member
Rimfire Benchrest Folks...

I have one of those nifty XP-100 pistols converted to .22LR. It is an amazing little gun that is killer accurate and so much fun to shoot. I didn't get it new, but it came set up this way, with a Leupold 40x Competition scope on a standard Weaver base.

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Bill offered to make me one of his single-base, double-ring mounts, so I got a new Weaver base and sent it off. Then he asked me to run an experiment for him. In his own words:


The first spearment to do is this:

Foul the bore, then shoot a couple of groups..........then, remove the cross bolt from the rear ring, then remove the top strap of the rear ring.

Then you can carefully slide the rear ring off of the base.......you might lift up slightly on the scope as you slide the rear ring off...

Now, with only the front ring holding the scope, foul a shot, then, taking the same aiming hold as you did for the first two groups, fire another group.

Now, see where this group strikes the target as compared to the first two groups shot with the scope held by both rings....


Here's the point of this spearment:

If the group you fired with just one ring holding the scope strikes the exact same location as the two groups using both rings, you have a perfect scope mounting system..........

If the one ring group strikes a different location, this shows that the scope was in a bind with the two ring set-up.

And, depending on how far apart the group locations are, determines how "bound up" the scope was in the two ring set-up. ( the single ring will hold the scope just fine...I've tested a lot of guns using just one ring)



I was able to get the first part of the spearment done this week. My target was set at 50 meters as that was the only distance I could utilize that day. I fouled the bore, then shot some sighters on the left, then a couple of groups, the center two The wind was at first light and steady, but I wasn't able to set out any wind flags due to the range event that day. Here's the two groups.

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Then I removed the rear cross bolt and ring half and carefully removed the lower ring. Then, without changing my aim point, I fouled the barrel and shot a couple more groups, with the following results.

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Of course, by now and with the range breaks I had to endure, the wind had picked up and become a bit switchy. Disregarding my poor wind guessing holdoffs, you can see these groups are definitely higher than the first two, and also not as small. Just to confirm, I shot a third group next to the original two, and it was also in the same location, higher than the original ones.

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Obviously, I didn't have a perfect scope mounting system...the scope was in a bind.

I hope to complete the second part of this test next week, with the new single-base and two-ring system, but besides seeing the light on the singe-base system (which I had read about and agreed to it's merits before this test), it raised some interesting questions for me.

One: The single-base mount is supposed to remove the binding in the scope mounting system, but this one had the Burris Signature rings with inserts already in place. Theoretically, that type of mounting should remove any binding in the scope, so my groups should have been in the same location as the original ones. Why did the point of impact move when only one ring was used?

Two: Is it possible that with only one ring in place, the scope could have moved when the rear ring was removed because of the plastic insert not being a solid metal to metal contact? It seems just a very slight bump when removing the ring, despite how careful I was, might be enough to cause that change in impact.

Three: I understand the Burris Signature ring system, and, like Wally and the others, I was always convinced it was a better way to go, In fact, I also use it on most of my guns. I can see how the plastic inserts can self-center when you first start tightening the ring halves, but as the screws are tightened further and the insert halves join together, can the tightening process cause those plastic pieces to become solid enough to end up binding the scope?



Since I haven't removed the scope yet and it is still mounted with just the front ring, I could go back to the range and try putting upward or downward pressure on the scope, shoot a couple of groups and see if the impact point changed. That would confirm whether I had bumped the scope to cause the vertical change on the targets or whether the scope was actually in a bind.

Maybe I will need to replace the Burris Signature rings and inserts and go with a solid Weaver ring setup. More to come later, when I can get to the range again.
 
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burris zee rings

The burris rings with inserts takes 2 rings to hold scope they are made like a trunnion bearing with just one ring the scope has nothing to hold it in line. you can take one finger and move other end of scope. Just like 2 trunnion bearings will hold a shaft straight 2 burris rings with inserts will hold scope straight. This how they can use inserts of different thickness as long as top and bottom inserts equal plus and neg numbers +10 on top must have neg 10 on bottom same as -20 and +20 must be used togeather. I am 99.9% sure I am right on this
 
Friend 80X80

Friend 80X80

Thanks for doing this spearment........

Here's what it seems to me:

Like Jim G said, it may take both rings for the system to work.........as designed.

Although, I will say this; your point of aim difference is really not bad at all......I've seen "several inches" of difference, testing this same way.

It would have been most interesting if the rings had been solid type...........may have not made any difference as the point of aim difference may have been exactly the same.......or much worse.........

And, kike you said, you may have moved things a little when you physically removed the rear ring.......maybe?

Soooooooo......I don't think your scope was in much of a bind, by your results.......so for a conventional scope mounting, those rings do seem to work good.

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A couple of other things to ponder:

One thing the floating insert rings would most certainly do, is to take care of scope tubes that are not perfectly straight......which lapping conventional rings won't.

And, the bulk of the RFBR actions, in use today, have equal height receiver rings, for and aft........unlike the XP which is stepped down in the rear.

So dealing with the XP is a worse case scenario.

Your friend, Bill Calfee
 
IHMSA80x80,

Burris designed those rings to use the inserts to point the scope as close to POI as possible before using the scope's adjustments by using offset inserts. Or just 0 inserts could be used and a traditional sighting in is called for. I say that to ask this: Did you have the 0 inserts in the rear ring or one of the offset? (5, 10, 15, 20) I would think if one of the offset were in the rear that POI would change a decent amount in an experiment like this.

The inserts aren't a hard plastic so I do think there is some compensation in the plastic used that keeps from binding the scope versus typical rings. In my opinion at least.
 
The burris rings with inserts takes 2 rings to hold scope they are made like a trunnion bearing with just one ring the scope has nothing to hold it in line. you can take one finger and move other end of scope.

Even if it was solidly clamped by the front ring?

I plan to check this out next time at the range, to see if I can move the single ring-mounted scope and whether any pressure I apply to the scope will change point of impact on the target.
 
I say that to ask this: Did you have the 0 inserts in the rear ring or one of the offset? (5, 10, 15, 20) I would think if one of the offset were in the rear that POI would change a decent amount in an experiment like this.

I did not do the original scope mounting on this XP, but I just went and looked, and the plastic ring inserts that I removed from the rear ring are both marked "0". When I remove the front ring, I'll post which inserts were installed there.
 
Friend 80X80

Thanks for doing this spearment........

Although, I will say this; your point of aim difference is really not bad at all......I've seen "several inches" of difference, testing this same way.

It would have been most interesting if the rings had been solid type...........may have not made any difference as the point of aim difference may have been exactly the same.......or much worse.........

And, kike you said, you may have moved things a little when you physically removed the rear ring.......maybe?

Soooooooo......I don't think your scope was in much of a bind, by your results.......so for a conventional scope mounting, those rings do seem to work good.



Your friend, Bill Calfee


I was surprised by the difference in impact points of the different groups. I had thought if there was any difference, it might have been very little. Several inches is a lot of difference!

Tuesday I will test it with the original front ring only, just like I left it after the first part of the experiment, to see if I can move the scope up or down and change the impact point.

Then I can install the new base you sent and do the second part of the spearment.

Do you think the new single-base ring system will work as well if I continue to use the Signature rings, or would it be better to swap those for standard Weaver metal rings?


Friend Dean
 
Dean,

How tight do you tighten the bracket screws. I think Burris only recommends 14-18 inch pounds. Doesn't seem like much but from what I gather it doesn't take much. I tried the same thing a few years ago and had no real difference. It could simply be the scope. If you have perfect alignment and the scope is not perfect there may be a bind. You don't have much of one if any.

Wally,

I bought this XP already set up this way. Someone else tightened the screws and I haven't checked the torque, only checked with the torx wrench to see if any of them were loose when I got it.
 
I did not do the original scope mounting on this XP, but I just went and looked, and the plastic ring inserts that I removed from the rear ring are both marked "0". When I remove the front ring, I'll post which inserts were installed there.

That answers all I was curious about!

I would think the lateral movement change in POI would be the most important result as far as the bind experiment goes though I'm like wmsmallwood, I would have thought the POI would have shifted downward instead of up.
 
If the back of the scope rises when the screws are released then the impact should rise.
Kim


That is true. My reason for doing some more testing tomorrow is to see if my point of impact change on the target was a result of me putting a slight upward pressure on the scope when I removed the rear ring, even though I was very careful to not do that.
 
I was able to get to the range yesterday. After fouling the bore, I shot a few rounds to check the wind conditions and confirm the point of impact was the same as the previous time. It was. Then I applied some hard downward pressure in the back of the scope in the single mount.

A couple of groups were fired with no other changes, and yes, the point of impact moved downward quite a bit, so I may have bumped the scope on the first day, while removing the rear ring.

I then removed the front ring and scope, removed the original base, and installed the new single-mount base on the front receiver ring. Then I remounted the scope using the same Burris Signature rings. I was able to get the scope re-zeroed at 50 meters, but wasn't able to shoot any groups to see if the single-mount base system was any more accurate than the original one. By then, the wind had picked up considerably, so testing would have been inconclusive. Part two of the spearment will have to wait until next range day.
 
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Friend 80X80

I was able to get to the range yesterday. After fouling the bore, I shot a few rounds to check the wind conditions and confirm the point of impact was the same as the previous time. It was. Then I applied some hard downward pressure in the back of the scope in the single mount.

A couple of groups were fired with no other changes, and yes, the point of impact moved downward quite a bit, so I may have bumped the scope on the first day, while removing the rear ring.

I then removed the front ring and scope, removed the original base, and installed the new single-mount base on the front receiver ring. Then I remounted the scope using the same Burris Signature rings. I was able to get the scope re-zeroed at 50 meters, but wasn't able to shoot any groups to see if the single-mount base system was any more accurate than the original one. By then, the wind had picked up considerably, so testing would have been inconclusive. Part two of the spearment will have to wait until next range day.

Friend 80X80:

Whether this scope mounting system gives an accuracy advantage over conventional mounts is still an open book...

The idea of it, is to help your gun shoot its best accuracy day in and day out, especially during temp changes......

I fully expect your accuracy to be a wash with it, compared to your traditional mounting.......

But, once you play with it enough to form an opinion, if you find that your gun actually produces better accuracy, then you will be another vote in that direction............

I've had several folks change to my scope mounting system, to keep their guns working day in and day out, and as a bonus, find their accuracy slightly better, to boot...

But, the final disposition is still to be determined.......


Your friend, Bill Calfee
 

Friend 80X80:

Whether this scope mounting system gives an accuracy advantage over conventional mounts is still an open book...

The idea of it, is to help your gun shoot its best accuracy day in and day out, especially during temp changes......

I fully expect your accuracy to be a wash with it, compared to your traditional mounting.......


Your friend, Bill Calfee


Friend Bill,

I fully agree that your single-base scope mounting will maintain the gun's best accuracy on a daily basis. I can see that the traditional mounting systems can easily induce scope stresses...they just have to. That could explain why guns seem to need a few clicks to re-zero each time you shoot them.

Next week, I will try to test the new mounting system, now that it is sighted in again. We'll see if there are any accuracy advantages over time. It may not change, but I will feel better using the new mount.


Friend Dean
 
Managed to get to the range this week and test the new single-base scope mount. Conditions were fair. The target looked like some of the other ones I shot with this gun in the past...nothing obviously better, nor any worse, at least. I'll keep at it when I can. It sure did draw a lot of comments from the other shooters, though.
 
Friend 80X80

Managed to get to the range this week and test the new single-base scope mount. Conditions were fair. The target looked like some of the other ones I shot with this gun in the past...nothing obviously better, nor any worse, at least. I'll keep at it when I can. It sure did draw a lot of comments from the other shooters, though.

Friend 80X80

I expected the accuracy to be at least a wash...........

Expecting an immediate accuracy increase isn't why I adopted this system............the other issues with scope mounting are what I was trying to correct.....

The possibility of an accuracy increase came later, initially, when I started doing my through the scope movies............thinking the added weight of the camera hanging off of the scope was the cause..........still do..........but the school is still out about this accuracy increase....

I have begun to notice something related to a possible accuracy increase.............

The folks who've tried my scope mounting, who use the big Nightforce scopes, are the ones who believe they actually received an accuracy increase......

But again, school is still out as to the validity of my system maybe giving an accuracy increase............



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The reaction you had to it was like it was for me when I first shot a match with my scope mounted, as such...........

I will say this; we're seeing more and more folks mount their scopes in this fashion.........and for good reason..........it does solve some scope mounting/bedding issues.........

I have a feeling, as we proceed, that more and more folks will start using this..........again, for a very practical reason: They want their gun to perform at 100% every time they compete..........whether it's 100 degrees or 50 degrees...........

For best results though, the third hole really needs to be drilled and tapped..........
(by the way, this is one very positive thing with the new Turbo products...........those actions come with the third hole................all actions should be drilled this way, cause the world of big time RFBR is slowly evolving to this method of scope mounting...........and like I said, for very sound and practical reasons.......)

Your friend, BC
 
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I finally got some pictures of the new scope mounting system. Since the last post, I have been able to shoot this only a couple of times. Neither time did I have any good conditions, just ok, so no real idea of any accuracy improvement. As Bill said, it will take more shooting to see if there is any advantage, but I do like the set-up. The gun was consistent in shot placement both times with the temperature between the two days about 20 degrees different. No adjustments to the scope had to be made. Tomorrow's range day looks iffy again.

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"so no real idea of any accuracy improvement. As Bill said, it will take more shooting to see if there is any advantage, but I do like the set-up."

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Friend 80x80:

Excellent pictures........

Dean, from all of my work with this scope mounting system, I sorta doubt there will be an actual accuracy increase with scopes like your L-comp or the Lyman AA's that I use...........

The main benefit is the correcting of some long time scope issues, and bedding issues, when traditional mounting is used across the loading port...

I'm tending to believe that the beneficiaries of any accuracy increase are the users of the big NF scopes......

One other kinda interesting point about this mounting system:

If you look at your original, traditional mounting, and look at the amount of overhang of the scope, then look at the current mounting, it is most obvious that the way you have the scope mounted now more perfectly balances the weight of the entire scope, for and aft, between the rings.


Folks like the "Raging Inferno" may, and I repeat may, be gaining an accuracy increase with those NF scopes.....

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Or someone like Tom Wilkinson, with his NF may also be gaining some accuracy increase...

wilkinson%20scope%20base.jpg


Here's a picture of one of my Lyman AA's showing how perfectly balanced the scope is with my scope mounting system.

When I have this scope mounted across the loading port in the traditional way, a much greater percent of the weight of the scope hangs off the front end..........which, if, there's some kind of accuracy advantage, it's the wrong way.....I actually may be killing some accuracy by having so much of the scope's weight hanging off the front.....

scope%20on%20magic%20marker.jpg


Your friend, Bill Calfee
 
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That is a great picture. Sure does balance the weight evenly.

Unfortunately, my range day was rained out again.


Friend Dean
 
Friend 80x80

That is a great picture. Sure does balance the weight evenly.

Unfortunately, my range day was rained out again.


Friend Dean

Friend 80x80:

CYA is strictly about advancing rimfire accuracy.

Can't wait until you get to test further.....

Your friend, Bill Calfee
 
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