Installing a Scout Scope Mount on a Mosin-Nagant

Copyright 2007 by Junior Doughty Update here.

 Click photos for full size popup versions.

I did all the drilling mentioned here on a $99 portable drill press. If I can do it, so can you.

All drills & taps, etc., came from Brownells. See below for a list of tools and parts used.

I had an extra 3x pistol scope hanging around the loading room, so I decided to put it on my $80 M-38 Mosin-Nagant via a scout scope mount. An Internet search found suitable mounts priced from $85 to a low of $15 from H Town Imports. I couldn't see paying more for a scope mount than I did for the rifle, so off went $15 + shipping to H Town Imports. A few days later, the mount arrived. It was made in China as expected. However, the Chinaman who designed it didn't know about a fellow named Newton and his law of inertia: An object at rest will remain at rest unless acted upon by an external and unbalanced force.

Click for full size popup photo The mount was designed as if the scope did the recoiling, not the rifle. The rifle recoils to the right in this picture, and thanks to Newton the scope wants to stand still. In effect, the rifle goes backwards and the scope and mount twist counterclockwise, pivoting around the cross-screws. You see one hex-head cross screw in this photo—both hereafter know as the P or Pivot screws. In other words, the back of the mount goes up, and the front goes down. In only three shots, the scope and mount rattled back and forth.

I moved the scope to the very rear of the mount and tried again. The same thing happened—rattle, rattle.

Click here to see another way to skin this cat.
I solved the problem by drilling & tapping the front of the mount for an 8-40 screw—hereafter known as the A or added screw. I wanted to leave this ol' combat veteran rifle as close to original as possible, so I drilled & tapped through the rear barrel band. If I ever wanted to restore the rifle to its original state, putting an 8-40 plug screw in the band someday would look better than a filled hole in the wooden forearm. (Yes, I know I have to remove the scope in order to remove the forearm.)

The A screw pushes against the barrel and prevents the mount from twisting. You can see the A screw clearly in the large version of the photo above. I cut the screw off even with the top of the mount and slotted it with a hacksaw.

Click for full size popup photoHere we see the right side of the mount. The rifle recoil in this case is to the left. The front edge of the mount acts like a recoil lug against the lip of the military sight base. I carefully filed the leading edge of the lug so that the lug contacted the lip when the P screws were tightened. That moved recoil forces from the P screws and onto the lug.

Note: By filing one side of the mount lug more than the other side, you can align the mount Left & Right with the barrel.

Notice the cone-tipped screw—hereafter known as screw B. In use, its tip pushes against the top of the military sight lip and forces the front of the mount upwards.

Above, you can also see one of the two rear screws—hereafter known as screw C and screw D. Their function is to push the rear of the mount upwards.

Click for full size popup photoThis photo more clearly shows the relationship of the screws. This H Town Imports mount is in the process of being installed on an $80 M-44 Mosin-Nagant for use with a red dot sight. The A screw has just been installed and awaits a date with a hacksaw.

Screws A, B, C, and D all push upwards and force the mount against screws P.

Notice there's only about 1/4" between screw B and the Pivot screws P. No way can screw B overcome counterclockwise rotational recoil forces without the help of screw A. Without screw A, recoil twists screws P and pulls screws P upwards. The result = a loose mount.

Well, I whacked off the mount in front of screw A and installed a $28 Simmons red dot sight. Three shots later, I could wiggle the mount. (Insert curse word here ____!)

  • I should have put screw A closer to the front of the mount like I did on the 3x pistol scope mount for the M-38.

  • I should have noticed how top heavy the red dot sight was compared to the 3x pistol scope.
Click for full size popup photoHere's a look at the red dot sight and at the final solution.

The numbered knob contains the battery and is located at the very top of the sight, i.e., most of the sight's 7.7 oz mass is way above the center of the sight. Plus, it's almost 3 1/2" from the top of the battery box to the centerline of the rifle bore. At recoil, the rifle moved to the right and the sight, top heavy and with lots of leverage, twisted counterclockwise—probably bending the mount momentarily and moving screws C and D up and off the barrel.

Look closely above and you'll notice that the metric ~1/4" diameter Chinese screw C is now an American 8-40 screw. It is clearanced through the mount and is drilled and tapped into the military rear sight. It now prevents the rear of the mount from moving upwards. Notice also that I've provided screw D with an 8-40 locking set screw on this side in addition to the Chinese supplied locking set screw on the other side. Maybe 100 heavy loads later, this mount hasn't even wiggled.

Click for full size popup photo Pay particular attention to this photo looking down at the mount sans sight but with the sight base in place.

Notice how I carefully placed the sight base's lugs against the mount's lugs so recoil would push lug against lug, preventing movement of the base/sight. Remember: the rifle recoils/moves to the right in this photo; the scope wants to stay still.

At the far left, see screw A and its hacksawed screwdriver blade slot.

Near the center, notice how 8-40 screw C is countersunk into the surface of the mount. I did that (a) to let the fillister screw head clear the edge of the mount lug; and (b) to give the flat base of the fillister screw head a flat surface on which to bite.

To mark the hole for drilling in the military sight base, I used a hole center punch which just barely fit inside the Chinese-drilled hole in the mount. I was afraid to drill into the barrel, so, by depth measurement, I stopped the drill just as it passed through the military sight base.

The hole for new screw C drilled & tapped, I leveled the top of the mount with the centerline of the rifle bore and tightened screws A, B, and D. Then I trimmed the end of screw C with a file until it fully tightened with 1/2 turn to spare. For more support, I could have used two 6-48 screws instead of or even in addition to 8-40 screw C. Click for full size popup photo

 If I had used a "holo" red dot sight with its much lower center of mass, I probably would not have needed to drill & tap for a new screw C.   Hindsight is always 20-20.

Here's the M-44 & red dot ready for the woods.

As you see it here it weighs 7 lbs 10 oz. The OAL is a handy 40 1/4" which is perfect for hunting in the thickets.

I added an Uncle Mike's sling swivel stud and a keychain ring so I could use one of my saddle ring slings on the rifle.
Click for full size popup photo
This rifle is hereby christened the Rain Rifle. How can a little rust hurt an $80 rifle? If it's pouring down rain I can don a parka and grab the Rain Rifle and hit the woods after ol' Mossy Horns. A Mosin-Nagant is easily dismantled. Back at camp, I can quickly take the rifle apart and dry it out.

A saddle ring sling will allow me to lean against a tree and keep my hands inside the parka and all dry and cozy while the Rain Rifle stays outside the parka all wet and ready. Sounds like a plan to me!

Here's an appendix about my $28 Simmons red dot sight. An identical red dot sight is sold under several brand names, but all of them probably originate in the same factory in China. Mine contained zero information about battery life. I own a sensitive ammeter, so I hooked it up to my sight's battery and checked the amperage at different scale settings. The scale around the battery box reads from 0 to 11.

According to the CR 2032 battery in my Simmons red dot sight is a 240 mAh battery. In other words, it can push out 240 milliamps for 1 hour. Or 24 milliamps for 10 hours. Or 2.4 milliamps for 100 hours. So. . . .

    on 1 = .087 mA = 2758 hrs
    on 5 = .635 mA = 378 hrs
    on 11 = 9.0 mA = 26 hrs

My dot is plenty bright on 5, so I'm not worried about battery life.

Here's the list of tools and parts from Brownells:

Screw A (both rifles):

  • 8-40 x 1" fillister head screw # 080-000-837

  • 8-40 tap

  • #28 drill for tap

Screw C (Rain Rifle):

  • 8-40 x 1" fillister head screw # 080-000-837

  • 8-40 bottom tap

  • #28 drill for tap

  • punch from hole center punch set # 080-732-000

  • #8 fillister sight screw counterbore # 080-671-841

Screw D (Rain Rifle):

  • 8-40 hex socket plug screw # 080-534-002

  • 8-40 tap

  • #28 drill for tap

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