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Over the years, I've mounted a number of optics on the rifles I've owned. I never gave it much thought since up to this point in time, the larger rifles were either used for deer hunting (shots out to about 200 yards max) or the smaller calibers for plinking. Accuracy was always good enough for the intended use.
A couple of months back, I decided to purchase a Savage 10 FCP HS-Precision bolt gun in .308 Win. I intend to use it at Front Sight or another training facility for precision rifle shooting. I'll use it locally with some of my shooting buddies when we do long range shooting.
After doing some research on optics, rings, and bases for my new Savage, it
became clear that scope ring alignment and fit weren't simply guaranteed because
you bought name brand rings. Slight differences in the recieiver, base,
and scope ring dimensions all add up to a misaligned scope ring. More
research showed that I could get a reasonably priced tool, made by
Engineering, that could correct this problem. It would allow me to verify
ring alignment and lap the rings if any adjustment was necessary. This kit
accommodates both 1" and 30 mm scope rings. It looked like a good deal so
I found a retailer and picked one up.
The Wheeler combo kit contains two sets of solid steel lapping and alignment bars to handle 1" and 30mm scope tubes. A handle is included for the two lapping bars. Along with the instructions, the kit also contains 220 grit lapping compound.
I already had a Tipton gun vise and it was was quite handy for
securing the rifle while checking alignment and performing the subsequent
lapping of the rings. If you don't have one, you may wish to consider
getting a gun vise. I also use it to hold my rifles when I clean them.
It really does make the job much easier.
The business end of the two alignment bars. After the lower scope rings are installed on the firearm, the alignment bars are placed into the rings. I positioned the bars so the gap between them was midway between the two rings and there was but a small distance between the points. The top half of the ring was then installed and tightened to manufacturer's spec.
It should be noted that one needs to keep the upper and lower rings paired together at this point. When removing and reinstalling the upper rings, switching the ring's location between the two lowers can certainly result in an alignment difference. Even keeping them matched but rotating a ring 180 degrees can cause issues in the alignment process. I used a piece of masking tape on the top of each ring to indicate the forward facing direction and its position (front or rear mounting ring).
At this point, I checked to see how the alignment bars looked. A proper alignment will have the two points both horizontally and vertically aligned with each other. If it is not quite in alignment, and you are using dovetail mount rings, rotate them slightly to improve the alignment. Similarly, if the rear ring is windage adjustable, try moving it to get a better alignment. It is possible that you may even have to shim the front or rear base (assuming you are using two piece bases) to get the bar points to align. In my case, I was using a one piece picatinny base with corresponding rings. I had good alignment and so was ready to proceed with the last step, lapping the rings. Lapping will only remove minor alignment issues so one can not rely on it to "fix everything" if there is a problem.
Now satisfied with the alignment, I removed the upper rings and then the alignment bars. I threaded the handle into the 30mm lapping bar and applied a bit of the 220 grit abrasive compound to the bar. You can see the light gray compound on the bar in the above photo.
With the lapping bar laying the lower rings, I replaced the upper rings (noting their appropriate positions) and just barely tightened the screws. One needs to be able to rotate the bar side to side and front to back in what is best described as a figure 8 pattern. If the rings are too tight, the bar will not be able to be moved. Also, you don't want any slop in the rings....a sloppy fit will allow the bar to wobble around in the ring. Doing so will cause improperly lapping and not contribute to improving the alignment and the ring's grip on the scope tube.
After about 90 seconds of rotating/sliding the lapping bar, I removed the upper rings and set them aside. I removed the lapping bar and then wiped the lower rings clean. I also wiped the upper rings clean. As you can see in the above photo, approximately half of the original black finish on this lower ring has been "scrubbed" away by the 220 grit abrasive compound. These "high spots" are now being lowered so that more of the ring's surface is in contact with the scope tube. In doing so, the ring's ability to evenly clamp the scope in placed is greatly improved and the chances of it shifting under recoil are very much reduced. Likewise, having an even clamping surface distributes those forces so there are no binding spots on the scope tube.
Next, I examined the remaining three ring halves to see how they looked. I put the lapping bar back onto the lower rings and carefully reassembled the upper rings, again noting their correct orientation. About another 60 seconds of lapping action gave me nearly 100 coverage on the rings. One doesn't want to get too carried away with the lapping process. Trying to put material back on the ring is quite a challenge <grin>. There will be an obvious difference between steel and aluminum rings in regards to how long the lapping process will take. The steel rings will not lap in nearly as fast as the aluminum rings.
Another wipe down of the rings to remove the abrasive compound and another check with the alignment bars verified things were looking great. I declared the alignment and lapping process to be complete.
If you were wondering what was getting mounted, here is a photo of my .308 Winchester Savage 10 FCP HS-Precision rifle. I used a one piece 20 MOA EGW base with Burriss XTR 30mm rings. The scope is a Bushnell 4200 6x24-50mm first focal plane mil-dot illuminated reticle.
If you are wondering how it works.....read on.
My 2nd trip to the range for working up a suitable handload yielded the above group @ 100 yds. During my 1st trip, four of the five loads resulted in sub-MOA groups. The above group was shot with 168 gr. Sierra Match Kings using Varget powder and Winchester brass. At this point, I've only worked with this one bullet weight and powder so there are still lots of opportunities to experiment with other combinations.
The Wheeler Engineering Scope Alignment and Lapping Kit worked very well. I had no problems what so ever with it. I decided to purchase one for my new rifle and scope since it was just a small fractional part of what I spent on the total project. I am looking to get the best performance from my .308. Going cheap when mounting the scope just didn't seem like the best way to achieve that goal. So far, I'm very happy with the Savage's performance and I look forward to squeaking a bit more out of it.
See you at the range!