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Picture of Making the scope on your Mosin Nagant stay put
The Mosin Nagant is a rifle first built by Russian and French firearms designers in the late 1800's. It's a reliable weapon and was used in the Russian military before and after the revolution.

Today, the surplus firearms market is saturated with these firearms, which are typically on display by the case at local gun stores. Their caliber (close to .308) allows them to be used for cheap hunting rifles, and they are pretty accurate, reliable, and tough.

The challenge with these firearms is that the 3/8 sight rail is a bit anemic for mounting a scope. A common problem with them is for the sight ring screws to loosen up after a few rounds (even with locktite).

This instructable documents my 3rd (yes third) adventure in mounting a scope to my Mosin Nagant M91/30.

Note: This documents me making permanent modifications to a firearm. I am NOT a professional gunsmith and am not responsible in any way if you make modifications to your firearms. If you are not comfortable with the modifications in this instructable either structurally or for retaining historical value...don't do it! If you perform this modification...IT'S ON YOU !
 
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Step 1: Required hardware

Picture of Required hardware
For the hardware, steel is ok. I like to use stainless steel, but couldn't find it in such small hardware.

(4) Metric #4-.70x12 Cap Screws
(4) Metric #4 Wave Lock Washers
(4) Metric #4 Split Lock Washers
(2) 10-32x1/4 Set Screw
(1) 1/16 Allen Wrench (or whatever fits the set screw).
(1) Tube of locktite.
(1) 10-32 tap
(1) #21 Drill bit
(1) pair of medium height 3/8 dovetail scope rings (I used the cheap NCStar ones off Amazon).

With the sight rings, but not including the scope, I have about $15 in the mod.

Step 2: Drill a hole in the scope ring bases

Picture of Drill a hole in the scope ring bases
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Drill a hole EXACTLY in the middle of the scope ring bases centered between the bolt holes. Drill the holes all the way through.

Step 3: Dimple the rifle

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NOT FOR THE FAINT OF HEART!!!

If you value the historical accuracy or doubt the structural integrity of this mod, then don't do this step!

Dimple the 3/8 sight rail of the Mosin Nagant where the set screw will be tightened. I've assumed the rear iron sight has been removed.

   * Position the sight rings on the rail where you want them and snug the mounting screws. Helps to have the scope on hand to mock up where you want the rings.
   * Use the same drill bit used for step 2 and a hand drill to drill down through the hole in the sight ring base and "dimple" the sight rail on the gun.   
   * The dimple should only be as deep as the head of the drill bit (just barely - see picture).

Step 4: Tap the holes

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Run the 10-32 tap all the way through the hole. These aluminum scope rings were easily tapped with the tap mounted in a drill.

Step 5: Add the set screw

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Thread one set screw into each base from the bottom, but such that the head of the set screw points up. The "point" of the set screw should point down.

Step 6: Add the Sight Rings

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Instead of the cheapo allen screws on the side of the sight rings (which stripped the head out the first time around), use the cap screws with a split lock washer and wave lock washer for each of the side mounting bolts. The larger head will give more support to mount with, and you can crank on the head a little tighter.

1. Inch the newly added set screw out slightly.
2. Position the sight rings in the right spot so that the set screw points "fall" into the dimples. Keep in mind which ring goes to the front and which goes to the back.
3. Add locktite to each side mounting screw and thread them back into the sight rings.
4. Tighten the side mounting screws to their final tension (set screws should be completely over the dimples). If sight rings are aluminum and threaded to accept the side mounting screws, be careful not to tighten so hard you strip the threads.
5. Tighten the set screw to it's final tension using the allen wrench through the top of the base.

Step 7: Add Scope

Picture of Add Scope
Add the scope to the rings and bolt it down.

Your done. Go sight it in. This is my 3rd attempt to mount a sight to this gun. I ran 13 rounds through the gun after this and it was still rock solid.

Good hunting!
RCS829 months ago

Why not use one of the systems designed for mounting scout scopes to the mosin that keep the rear leaf sight intact, while securing the scope. i.e Brass Stacker mount, or UTG TriRail mount. This allows the modification to be reversed in case you ever want to sell the rifle to someone who dislikes your mods.;

RC. I find the rear leaf sight mounts rarely stay solid. If you are lucky enough to find a solid shooting Mosin in a pile of surplus you will want a very solid mount. I have a UTG on my run of the mill surplus (10in groups @200yrds) but use the 3/8 dovetail for one with that shoots above expectations(2in groups with match ammo @200yrds). I agree that typically it's good to not modify a firearm beyond the point to turn back but it is a Mosin Nagant and most people will just get their own surplus from a dealer. Half the full of a Mosin is refinishing it and making it your own.

mallen451 year ago
I foud a way mount a scout scope with no damage to the gun. Just dont lose the sight. You need two of these. http://i00.i.aliimg.com/wsphoto/v0/688696782/VO-1pair-3-8-11mm-Dovetail-to-7-8-21mm-Weaver-Rail-Adapter-Mount-Matte-fit.jpg,digh. http://i00.i.aliimg.com/wsphoto/v0/688696782/VO-1pair-3-8-11mm-Dovetail-to-7-8-21mm-Weaver-Rail-Adapter-Mount-Matte-fit.jpg

BSA sella them, but they are available for cheap on eBay,and amazon. They appear to be identical the the ones from BSA

They end being a snig fit. That's good. Drift them on with a wooden dowel. Then tighten the screws using loctite. It on there good. I have had a couple 1000 round s with one of those.
cwesner1 year ago

I wanted to do this but I liked the scout scope configuration I got from big 5 that is made by AIM Sports Mosin Nagant combo pack. Works pretty good to about 200 yards but past that I haven't had the opportunity to shoot at a target yet. The P.U. scopes I have seen online and in stores are to expensive for a surplus rifle like the Mosin. plus they really have no magnification like the scope I have on it now. Good job on the instructable. I might end up doing this to mine in the near future.

Lucky7x72 years ago
Don't take this as abusive or negative but Please stop molesting the Mosin. She is a wonderful rifle just the way she is. If you need a scope buy a PU sniper version of the M91/30 but please oh please stop sporterizing them. PLEASE : ) but I digress she is yours and you are free to dress her as you see fit. Good Day
I agree. Modifying a Mosin for sporting is like sharpening an antique sword for trailblazing.
rizingf3nix (author) 2 years ago
The two dimples on the top of the rail I put there for the set screws to grab onto. The two holes on the side of the rail are original to the rifle. The two pins that hold the original rear sight slide into them.
zacker2 years ago
what's the two holes for? did you make them? I don't have them in mine and im trying to mount a scope to my Mosin but im not using the rail because its too far away for my scope and I don't really want to buy a new scope...lol
tyeo0984 years ago
Id just tap the receiver so I wouldnt have to deal with long eye-relief scopes.
Neat 'ible though, Locktite is very useful!
the trouble with tapping the reciever in a 91/30 is that the bolt action is at a square angle. you'd have to either replace the whole bolt, or have a smith bend it down to something like 60* which is absolutely horrible to work with.
rizingf3nix (author)  Tinker833 years ago
ATI actually has a great kit that includes a bolt handle and rear sight mount with very good instructions. Anyone with simple machine skills will be totally comfortable with the installation. It also holds a full scope quite well.
nickitzi3 years ago
One problem I find with this mod is that you are using rimfire scope mounts on a centerfire gun. What I would recommend using a universal weaver mount and drill and tap four 6-48 screw holes and remove all possibility of scope shift,
most rimfire mounts lack any real holding power even on the intended gun the use of set screws is a old gunsmith kink. PS I think it is great you did not use the worthless rear sight mounts.
rizingf3nix (author)  nickitzi3 years ago
The scope setup of the platform in general doesn't give many options short of diy gunsmithing, which at the time I wasn't comfortable with. Since this instructable, we've put about 300 rounds through the gun and it still hits where expected. Nothing has loosened up, but I would agree that rimfire rings aren't the best thing for it. So long as they hold...

Ironically, I've recently purchased an M44 (carbine version of a 91/30) and fit it with the ATI rear sight mount, subsequently putting about 20 rounds through it. The accuracy was astounding (using a Russian VOMZ scope) and I prefer shooting through it rather than the 91/30. The sighting for the scope mounted over the bolt feels more sure of itself. I'm looking forward to fall deer season with this gun.
tyeo0984 years ago
Also, your mosin could use a good refinishing with something other than 100yr old varnish!
that's not varnish... thats cosmoline...
rizingf3nix (author) 4 years ago
Update on the scope mod. I've since put about 100 rounds through the rifle, and the scope is still holding zero.