Proper Scope Mounting

ThePunisherNS

ThePunisherNS

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I ran into a bit of a problem at the range the other day and hopefully some of you have some ideas that may be able to correct the issue. I recently mounted a Bushnell Legend 5x15 variable scope with Weaver Tactical Rings and a Weaver One-Piece Multi-Slot Base on my Remington 700 SPS Tactical in .308 Winchester. I went to the range to sight the rifle in...starting at 25 yards, 50 yards, then finally 100 yards. By the time I was semi-sighted in at 100 yards the scope had no more elevation adjustment left. I was shooting Winchester 180 grain Power Points and everything (rings, base, and bipod) were tightened down, so I'm a bit confused on why the scope has maxed out its elevation at only 100 yards. Any input would be most helpful!
 
According to Bushnell, this model has an adjustment range of 50" at 100 yd or 50 MOA. It's not uncommon to find long range scopes with 80 MOA adjustment range, so 50 MOA in your case should be more than adequate and if your out of range, you have something that is drastically wrong.

If you have a Bushnell boresighter or a similar device, I would check the range of adjustment on the screen of the boresighter. I would also check to see at what spot on the adjustment range you are at the center of your screen.

The scope might be defective or either the rings/base are not correct.

Please keep in mind that you can do some of this assessment by comparing what you see through the barrel compared to what you see through the scope. When looking through the barrel, I find that if I used a shell with the primer removed, I'm able to come up with better results.

Please let us know how you make out.

Duke1
 
A shim under the rear of the base that measures .025"-.030" should give you 20 MOA (based on my rough math not knowing how long the base is).
 
We usually always shim the rear base of the Remngton rifles. The rifle maker and the base maker have not chatted in years it would seem. Bushnell's have very little internal movement, either a tapered base or tha shim will fix you up.

Scott
 
For each .001 thickness of shim you will go up approximately 1 MOA at 100 yds. This is a common problem and seems to be on the increas. Lately I have had Tikas, Remingtons, Savages and Kimbers that required shimming. Your dealer or gunsmith should have shims.
 
If you use a flat shim at one end, won't you risk warping the one piece base and putting the rings out of alignment with each other? I've never done it, but i've heard of using epoxy and a piece of wire the right thickness to hold the base off the reciever the right distance while the epoxy hardens.
 
Before using shims, I would want to know why. As I mentioned in my earlier post, this scope has a 4 foot plus adjustment range at 100 yd so if you're out of adjustment, something is wrong.

My first task would be to measure the difference in thickness between the front of the one-piece base and the rear. This can be easily and accurately done with a caliper or micrometer (preferably digital). You could find out on here what the difference should be. If this difference does not agree with the specification value, I would return my base and get a replacement.

On the other hand, if the base dimensions are correct, I would check the difference in height of the front and rear base mounting platforms - this can also be done accurately using a couple of different techniques.

If the heights of the platforms and thicknesses of the base ends are within specifications, then what you have left is the scope.

I would only use shims if these platforms are not according to specifications. I realize that not everyone has the proper tools to verify these things but most professional gunsmiths should be able to do it.



Duke1
 
It is not his scope or the mounts, it's the rifle. Remingtons, for some reason, have that flat machined more that is required, the rear of the scope/base sits lower and you run out of elevation.

Scott
 
m39a2 said:
It is not his scope or the mounts, it's the rifle. Remingtons, for some reason, have that flat machined more that is required, the rear of the scope/base sits lower and you run out of elevation.

Scott
Click to expand...

If this is the case then you have no choice but to use shims ..... just hope my SPS is not the same but will keep this in mind when installing my optics. Will make sure to check the adjustment range of the elevation using my boresighter before taking the gun to the range.

Duke1
 
I'm using Burris rings and inserts to make sure my elevation adjustment is near the bottom when I zero the gun, so that I have lots of room to go up for greater distance. I'd hate to have lost over half the elevation just to have the rifle zero at 100 yards.
 
I just measured the thicknesses of the 2-piece bases for the 700 LA/SA (Weaver 35 & 36) and the difference in their thicknesses is around 0.125", depending on how it is measured. This difference is a bit difficult to measure accurately because the bottom of the bases are not shaped the same.

Now all that I would need to do is measure the difference in height of the base platforms on the gun.

I'm in the process of getting a 1-piece picatinny rail for my 700 SPS LA and will be anxious to finish my measurements to check to see if my gun might have similar problems:(.

Duke1
 
Ive had the same problem with both Remington SPS V's... one in .204 and the other in .308.

Scott is right, its something to do with the base on the action.

I used.. 4 popcan shims... I think... thickness on the back ring for both my guns. The scopes were both Bushnell Elite 3200 Tacticals, and I needed the shims before I could even get it to boresight.

The .308 now has NF 20 MOA base and rings and I dont have to shim it anymore.
 
To determine if you have a height problem with the receiver of your Rem 700 do the following; take your one piece base and screw it down to the front mounting holes only then push the rear part of the base (there is enough flex in most bases to allow this) and if you have any movement then the rear mount point requires a shim. You may also be able to see daylight between the bottom of the rear of the base and the rear receiver. I think Remington must have changed their machining or jigs a couple of years ago as we have foung many new 700's require the shim in question. At some point I think the mount companies may change their dimensions as well to accomadate this change or at least supply a shim. Phil.
 
P of PDent said:
To determine if you have a height problem with the receiver of your Rem 700 do the following; take your one piece base and screw it down to the front mounting holes only then push the rear part of the base (there is enough flex in most bases to allow this) and if you have any movement then the rear mount point requires a shim. You may also be able to see daylight between the bottom of the rear of the base and the rear receiver. I think Remington must have changed their machining or jigs a couple of years ago as we have foung many new 700's require the shim in question. At some point I think the mount companies may change their dimensions as well to accomadate this change or at least supply a shim. Phil.
Click to expand...

Excellent suggestion........ I had heard about doing this somewhere but did not want to suggest it unless I had tried it first.

Thanks again for your input..... this is the first thing I will do when I receive my 1-piece base.

Duke1
 
Thanks for all the great suggestions! A colleague of mine, who is also an avid shooter, took a look at my rifle last night and made a few adjustments...my one-piece base hadn't been tightened down quite as much as it needed to be and my rings were a bit of the same. We switched the front and rear rings and reassembled it. I'm going to hit the range probably on Monday and see if those adjustments have made any difference. If not, I'll be contacting a local gunsmith to see if he can resolve the issue.
 
If you don't check to see if you need a shim and go ahead mounting your scope then you may have elevation problems as first noted but more importantly you would be putting undue stress on the maintube of your scope. Even if you use two piece bases I would still temporarily mount a one piece base to check if the problem exists. If you lap your rings this would also identify the problem in a visual indication of the rings not being in alignemtn with each other. Phil.
 
P of PDent said:
If you don't check to see if you need a shim and go ahead mounting your scope then you may have elevation problems as first noted but more importantly you would be putting undue stress on the maintube of your scope. Even if you use two piece bases I would still temporarily mount a one piece base to check if the problem exists. If you lap your rings this would also identify the problem in a visual indication of the rings not being in alignemtn with each other. Phil.
Click to expand...

Another good suggestion..... I do have a ring/base alignment tool so it would be easy to check the alignment of the rear mounting platform although the resolution of the alignment might not be adequate for a proper evaluation.

I will check this out on my 700 SPS and get back here. I do have a set of 2-piece base but my 1-piece rail is still not here.

Duke1
 
The problem has finally been fixed...my bases and rings simply were not quite tight enough and that caused the poor scope performance. I had my rifle out on Friday and shot a .75 MOA group at 100 yards with Winchester 180 grain Power Points. Needless to say, I'm a happy man now!
 
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