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Gunsmithing Rifles

How to Mount a Scope on a Swiss K31

by Gus Norcross   |  July 31st, 2013 1

I think most of you will agree that standing on a range hammering targets with an accurate bolt-action rifle is a lot of fun. My favorite rifle for this activity is the Swiss K31. Very accurate with a good trigger, and weighing less than 9 pounds unloaded, these are slick weapons readily available on the surplus market. My only serious gripe about the K31 is that I can’t see the sights very well, and if you’re not hitting the target, where is the fun in shooting? The barrel-mounted tangent rear sight might have worked for me in the ‘70s but no more. This rifle screams for either a receiver mounted peep sight or a scope.

Fitting a peep sight would require drilling and tapping holes in the receiver, and I’m not quite ready to make permanent modifications to this rifle. So I looked at scope mounts. Due to its vertical ejection pattern a scope can’t be mounted directly over the top of the receiver loading port. That leaves us with either a side mount or a “scout” type mount forward of the receiver. I have tried the side mounts from Swiss Products. They sell a permanent mount that screws to the left side of the receiver, which is quite solid but it requires drilling and tapping three holes. OK for a sporter, but doesn’t fit my criteria of no permanent alterations. The same company produces a clamp-on side mount which attaches to the right side of the receiver that works quite well. I set up a rifle with a 2-7X Leupold VX-1 and the clamp-on side mount (see pics). It worked fine except for a few brass marks on the scope body, and the slight offset of the scope to the right of bore centerline was hardly noticeable when shooting.

I was relatively satisfied with the side mount setup, but one day the nice people at Hi-Lux Optics sent me a new scope to evaluate. It is similar to the 2-7×32 scout scope I previously tested on the Garand but with a new .308 BDC reticle. When someone sends me a product to test I feel obligated to do so and I contemplated my options. Looking through the Brownells catalog, I came upon the S&K “Insta Scout Mount” for the K31.  The S&K mount replaces the rear sight, attaching securely to the rear sight base and provides 4 3/4 inches of Weaver style rail forward of the receiver. Attaching the steel S&K mount was a snap and I mounted the scope to the rail with Burris Zee rings to keep it as low as possible.

Minimum eye relief of the Hi-Lux scope is 8.7″ at 7X and is perfect for the K31. Most scout scopes are low power optics good for a quick shot at shorter ranges but not so good for target shooting at distance. With a variable power scope like the Hi-Lux I have the best of both worlds. I can turn it down to 2X and hammer targets off-hand at 50 yards or I can sit at the bench at 100 yards and test my handloads at 7X. The .308 BDC reticle is designed to be zeroed at 200 yards—center of crosshair—with hold-over marks for 300, 400 and 500 yards. The 7.5 x 55 K31 actually fires a .308-caliber bullet, although the brass casing differs from our own .308 Win and ballistics of the two cartridges are similar enough that I believe the reticle will work in this application.

Zeroing the scope was quick and easy with the finger adjustable elevation and windage knobs, although I found the knobs a bit stiff to operate. Once the rifle was zeroed, I loosened the two screws on each knob and zeroed the scales. The knobs provide positive, audible ¼ MOA clicks and are capped when not in use.

With the Hi-Lux scope, I was able to shoot sub MOA groups off the bench at 100 yards relatively easily firing Swiss 174-grain FMJ ammo dated 1978. A K31 is generally very accurate, and the addition of a good scope allows the marksman to shoot the rifle to its potential.

  • JT

    The BDC for this scope is probably set up for the Federal GM Match 168 grn 308. I compared the ballistics and trajectory of this round and the GP11 Swiss which uses a 174 grn bullet with a shape very similar to the Berger VLD. MV from a K31 is about 2560 fps.
    Using the Hornady ballistic calculator and comparing both rounds I believe you are correct when you state this reticle can be used for the GP11 round. The difference at 500 yards is less than 1″. At 300 yards the GP11 round should, according to the calcs, drop .4″ more that the Federal 168 grn. Those differences are less than the accuracy potential of the K31 (my opinion only!) Of course, I an assuming that this reticle is set up for the Federal GM Match.
    And the only way to know for sure is to take it out to the range! And a K31 with this scope set up would make the open class in vintage military competition tons of fun! 300.500/600 and 800 yards. Your basically shooting a vintage sniper rifle with a better scope than was available 60-70 years ago.

    Anyway, great review! I have a number of K31s and have been wanting to scope one with a scout set up. I have Swiss Products diopters for target shooting and their side mount for a scope and I think the set up you tested will be perfect.

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