There are several mfg.'s who make scope mounts for S&W's. The rear sight is removed, and the mount fits with a shoulder against the rear sight cut out. This withstands the most of the recoil. With lesser calibers, the older frames which were not drilled for scope mounts can use mounts such as B Square sells but heavy recoiling guns such as the .357 and .41 mag and .44 mag really need multiple screw down points. I'm not sure just when S&W began putting the scope mount holes in the top straps but it has been quite a few years. Finding a 686 with pre-drilled holes shouldn't be difficult.

Of course you can always have a good gunsmith drill & tap holes to install a scope mount. Collector value of the gun may be affected, but it is of no difference with a shooting gun.

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H Richard
SWCA1967 SWHF244