Mosin Nagant, PU Scope


January 23, 2012, 06:56 PM
Alternate Thread title: I'm an idiot who should just leave well enough alone.

Long story short I found a series of Surplus ammunition that my 1923 Mosin Nagant with PU scope loves. Blew out the X-ring at 100 yards on Sunday. It was snowing and about 24 degrees so I figure I'd take her out to the range and make her feel like she was at home.

So now that I had her sighted in and shooting well, I got to tinkering and fiddling and figured I would loosen up the adjustment knob screws and set them to zero. Hooray, she'll be accurate and dead on if I want to adjust ranges later on when I take her out for longer distances. First two large screws came out without a hitch, then was the smaller screw in the center that locks the adjustment knob.

Should have taken the hint when I had to go digging for a small enough screwdriver to fit it, but soldiered on and got it. As I was taking it out I didn't grab it right, fingers slipped and the screw zipped away on me. Just spent the last 2 hours with a magnet going over every conceivable area of my bench and the floor with no luck.

So. I know it's a longshot, but would anyone have any idea what size screw I would need? It's a barrel screw, no head on it.

This link has an exploded view of the turrets at the bottom, the one I lost is labeled Adj. Knob Lock Screw.

It's the smalle center screw in the exact center of the turret on this picture.

I was originally going to buy one of those gunsmith screw sets that they have for sale on Midway, but some of the research I did said the screws could be #4-32, #6-32, or #8-32. Not exactly sure what those numbers mean unfortunately but don't see those on any of the screw kits.

Just hoping someone here might have done the same kind move I made and might know the size off the top of their head.

Stupid screw is most likely hiding with the takedown pin of my Cetme that I never found?

Thanks in advance gentlemen for any possible help you might be able to give me.

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January 23, 2012, 07:29 PM
the screws could be #4-32, #6-32, or #8-32.It for sure won't be any Amercian thread like those.

It is a Russian scope, and it will use metric thread screws.

As for what those numbers mean?

6, 8 , etc is the diameter of the thread.
32, 36, 40, etc, is how many TPI, or threads per inch there are.

Metric screws will be like M1x.4mm, M2.x 5mm, etc.

Was I you, I'd keep looking.
It's got to be there somewhere.

Get a stong light and shine it near the floor at a low angle.
The screw will cast a shadow Ray Charles could see.


hang fire
January 25, 2012, 02:08 PM
I am sure 99.9999% of us have empathy for you, for we have been there too.

I found out long ago that using a small magnet is almost a waste of time. I bought few packs of the 1/2" magnets at Wally World and and glued them on to cover a 8"x2"x1/4" aluminum plate. Made a handle for it and now cover large areas with much more success.

Under my work bench resides many pieces of large and small ferrous metal and a magnet is useless. So when working on a gun & etc., made up a drop sheet to prevent the devilish small parts diving under the bench like they had eyes.

January 25, 2012, 04:38 PM
Yeah, should have learned my lesson after my Cetme retaining pin flew off to never be seen again. Probably today I'll lay down some paper, go down, pop out the remaining screw and take the calipers to them to get the measurements. I work in an R&D plant so I'm sure some of the scientists there have a book or two dedicated to just screws lol.

Knew it was a long shot but thanks anyway everyone. If I do find a proper replacement I'll be sure to update this for any poor soul who finds themselves in the same predicament.

January 25, 2012, 04:47 PM
Did you try the light & shadow trick yet?

Also, if all else fails, start with a clean & empty shop vac and sort through what you suck up with it.

The reason you couldn't find it with a magnet is because it is probably not magnetic.

May be stainless, or chrome plated brass.
Brass screws are often used in optics so they won't rust or corrode in place.


January 25, 2012, 05:09 PM
I'll vouch for the light trick. I've used it to find various screws. Handy for broken glass, too.

January 27, 2012, 04:56 PM
Yeah I'd use that light trick if I could. Dirt floor, old carpet. Love my work bench for the fact that I don't have to worry about solvent on the floor too much, but it makes times like these painful :(

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