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 Gun stuff from an industrial supply?

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Zeiss Ikon



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PostSubject: Gun stuff from an industrial supply?   Fri Mar 16, 2012 8:44 pm

Okay, so what's a piece of steel tubing got to do with a Mosin Nagant?

Well, in this case, this is 1" x 2" x .120" wall; that .120" wall gives a nominal inside measure of .760" -- which is exactly what my dial caliper reports as the width of the rear sight base on my 1943 Izhevsk 91/30. In practice, I expect I'll wind up having to sand the inside of the tube a little after cutting to shape, but this will get me to a Brass Stacker style see-through scout scope base in a significantly more fun way than just shelling out forty bucks or so plus shipping; it'll also let me customize the location of the rail (I have a piece of flat-bottom Picatinny rail six or seven inches long as well as a BSA red dot that'll going on here initially, though longer term I have my eye on an NCStar 2-7x42 pistol scope).

I plan to document the build with photographs posted here -- I'll start by cutting off a suitable piece from the six feet of tube I had to buy (from the industrial supply distributor I work for, so I got a pretty decent deal, about what I'd pay for just the six inches I really need from an online seller, by the time I figure in shipping), cutting it to shape, locating and drilling holes for extended versions of the pins that secure the sight base on the dovetail (I prefer pins over screws), then polishing up the surface and smoothing things out before bluing. Once done, I'll have clearance under the scope base to use the original sight out to (at least) 1000 meters -- and I should only add about six ounces compared to the lightest possible mount (given the weight of a stock 91/30, I don't think I'll even notice). Best of all, to return the rifle to original condition, I'll need only drive out the pins, take off the mount, and reinstall the original pins.

Now, if one didn't care about preserving use of the iron sights, one could use 1" square tubing and possibly even cut that down a little; one might also use 1" x 3" to get a little more clearance over the rear sight, but I honestly don't know what the iron sights are good for beyond five hundred meters -- I can barely see a man-sized target at that range without optical assistance, never mind locate such against a busy background. I don't have enough friends who shoot to make up a volley fire unit anyway (the only conceivable reason for the 2000 meter maximum on my Mosin's sights).

I figure I'll be able to get between eight and twelve of these bases out of the piece of steel I've got; I'll have to figure out something to do with the rest...
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Zeiss Ikon



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PostSubject: Re: Gun stuff from an industrial supply?   Sun Mar 18, 2012 4:40 pm

Okay, I got started on the build today. Nothing complicated, just cutting the actual work piece off the stock tube. First, I cut the end to the initial angle (the back end will actually have a notch cut out of this, but I wanted to get the work free of the heavy length of tube before dealing with that). Click on the thumbnails to see 800 pixel versions of these photos.

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Since I don't have either a power hacksaw or a bandsaw, nor a large enough angle grinder to mount a slicing wheel that could cut this size tubing, I made the cuts the old fashioned way -- with a muscle powered saw and miter box. The angle is to ensure that I'll be able to use all the elevation the height of the base permits without interference between the sight adjustment buttons and the scope base.

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Once the cut was well started, I pulled the stock out of the miter box to let me use a longer saw stroke.

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A few minutes more, and the first cut was done.

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Then I marked the length of the rail (to correct my first post, this is a Weaver, not a Picatinny rail piece).

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Finally, I made the second cut to free the "blank" from the stock tube. This is where I stopped for today; the humidity is huge outside and my arm is tired. Besides, I have to look around and try to find my (Harbor Freight) angle grinder and see if I have a wheel for it that I can use to clean up these cuts; my Dremel is a little on the lightweight side for this job.
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SilverTip
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PostSubject: Re: Gun stuff from an industrial supply?   Sun Mar 18, 2012 10:20 pm

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Zeiss Ikon



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PostSubject: Re: Gun stuff from an industrial supply?   Sat Mar 24, 2012 11:19 pm

Got a chance to do some more work on this build today (humidity was the enemy again -- turned into thunderstorms a couple hours after this).

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This was actually mid-week, I used my angle grinder to roughly clean up the cuts (mainly to remove the sharp burs left by the hacksaw cuts).

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I clipped what would be the base edge (taking care to leave the inside weld seam at the top, so I wouldn't have to grind it all off in order to fit the base over the rear sight). This was done in part to give a square edge to start the next cut.

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I cut off one edge of the tube, as close as possible to the wall, to open the tube into a channel (and leave as much height as possible). This was a long and tiring cut with a manual hacksaw, let me tell you.

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I got through it, though, and while it wasn't perfectly parallel to the narrow side of the tube, it didn't wander much over the length of the cut.

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The angle grinder came out again to clean up and even out the cut edge. I fix tools like this one (well, much more expensive versions) for a living, but this project is the first time I've actually used one off the job. Faster than a file, no question about it, but I'll wind up having to clean up the edges again with a file to get rid of the grit marks.

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Last one for today, I mocked up the base against the Mosin's sight. Next work session, I'll be notching in the rear end so it doesn't interfere with the adjustment buttons on the sight leaf, and contouring the front end to clear the hand guard -- both will probably be done mostly with the angle grinder. I'll also need to just touch the sight base with a file to take off a couple stake marks (which have no purpose I can see, they may be old damage that was blued over during the rearsenal), and then I may need to adjust the tension of the scope base walls so they lightly grip the sight base.
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PostSubject: Re: Gun stuff from an industrial supply?   Sat Mar 24, 2012 11:49 pm

Keep at it! Looks promising. Reminds me of the scope mount on my SVT I had.
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Zeiss Ikon



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PostSubject: Re: Gun stuff from an industrial supply?   Mon Mar 26, 2012 7:15 pm

I ran out of work today, so my boss let me come home early (without pay, but what can you do?). That gave me an opportunity to work on the scope base again.

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Because the sight adjuster and buttons extend beyond the base, I had to ensure the scope arch wouldn't interfere and prevent moving the adjuster forward to raise the blade. The simplest way to do that is to ensure that the scope base is no higher than the contour edge of the sight base, so I put a sticky note on the sight (carefully aligned with the bottom of the base), raised the blade to 1000 meters, then traced the base contour and marked the location of the adjuster (no need to cut away the scope mount further than that, I won't be able to see under the base at that setting, and couldn't hit anything smaller than an SUV with the open sights at that distance anyway). I also marked the length, since I'd need to notch to clear the hand guard.

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After carefully cutting the sticky note along the trace marks, I moved it to the work piece (again carefully aligned with the bottom edge) and traced the critical contour onto the steel (with a pencil, since I don't have a soapstone handy). I also transferred the handguard cut mark and freehanded a contour that would lighten the mount without compromising stiffness (much).

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Then it was outside with the angle grinder. This was a $20 tool, including the grinding wheel, and I've had it for ten years or more -- and I'm finding it's every bit as good as the smallest ones I fix for a living, which cost four to six times as much. Don't be afraid of Harbor Freight; I wouldn't recommend buying there if you make your living with your tools, but for hobbyists, it can save you a huge amount of money. I have this grinder, a spiral saw, a nail gun and tiny compressor, and most of my hand tools (hammers, files, punches, squares, protractors, and so on), as well as my dial caliper, all from Harbor Freight (and my lathe came from one of their spiritual kin, Homier), and while they aren't as pretty or, most likely, as durable as higher priced tools, they do the job, and are as accurate as they need to be.

Here, I'm about halfway through cutting the rear contour, just grinding away everything that isn't going to be part of the scope mount.

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And here, the rear contour is done -- I eyeballed the match between the two sides; I'm pretty good at that, but if I weren't, I'd have made a reverse pattern and transferred the contour to the other side. You may notice that the contour isn't the same as the Mosin rear sight base; it doesn't have to be, just lower so it doesn't interfere with the adjuster, and this was LOTS easier to cut (lots of file work to come, but when finished, it'll be prettier than a 1943 Izhevsk).

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This is the front contour -- I had intended to cut this deeper, for lightness, but I decided that, first, I liked this curve, and second, this would be stiffer (more meat under the front end of the mount). Not to mention this saved me fifteen or twenty minutes of grinding...

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And here's proof I'm pretty much done with the grinder for this project; the mount dry fitted to the sight base. The only changes from here to finished will be cosmetics, other than drilling the holes for the locking pins and drilling and tapping for the Weaver rail.

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Last one for today -- proof that I can raise the sight as far as will permit me to see under the mount, without the adjuster interfering with the scope mount.
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Zeiss Ikon



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PostSubject: Re: Gun stuff from an industrial supply?   Mon Apr 02, 2012 6:54 pm

Well.

I was going to do some more today (transferring the hole locations and drilling the holes), but I suddenly realized I don't have any metric twist drills, and my research indicates the sight retaining pins are 3 mm diameter. I have a 7/64" bit, but that's about .010" undersize, .108" vs. .118" for 3 mm -- and while twist drills generally drill a little oversize, I wouldn't expect to see them almost 10% over. If I drill the scope base to 7/64", therefore, I'll have to use undersize pins and the base will be prone to move back and forth, up and down enough to potentially throw POI off by a good foot at a hundred yards (not to mention eventually destroying the holes in the sight and/or the pins).

And since this payday was a little thin, I may have to wait until next payday (the 13th) to get a 3 mm twist drill and finish drilling the mount. I should, at that point, be able to get some 3 mm drill rod or similar to make the new pins, also.
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Zeiss Ikon



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PostSubject: Re: Gun stuff from an industrial supply?   Sat Apr 21, 2012 5:49 pm

Today's task, having acquired some M3 screws and acorn nuts, plus the #31 twist drill (0.120" diameter, vs. 0.118" nominal for 3 mm) required to drill for them, was to mark and drill the holes and test fit the base.

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Here's the method of marking the centerline for the holes, with a little rigamarole to get the line parallel with the top surface of the base instead of the (imperfect) bottom edge (and you might note I found my Dykem layout blue, which I could have used on the earlier profiling stages).

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And here I've marked the hole centers, transferred the marks to the previously scribed lines, and center punched accurately where the marks cross.

There's no photo of the next step at this time. When I drilled the holes (in the top side only, planning to use a transfer punch to mark for the bottom side holes, because I'm aware the holes for the sight pins wander a bit in some Mosins), despite what seemed adequate care to center up the twist drill in the punch marks (and using a drill press!), the drill wandered off the marks and the holes came out incorrectly spaced, inconsistently positioned vertically (which would cause vertical aiming error likely too large to readily adjust out), and too far to the rear (causing the base to interfere with the end cap on the hand guard).

There's no fixing this; I can't redrill without making the holes oversize, allowing the base to move under recoil, possibly enough to shear M3 screws and certainly enough to prevent holding zero. I'm going to have to start over. I've got lots more metal, but before I waste more time, I'm going to reexamine the operation path for this to see if I can't come up with better methods. Ideally, I'd like to use a vertical bandsaw to cut the end profiles (probably not possible; I don't even know where there's one locally that has correct blade speeds and enough power to cut steel), and find a way to mark and drill the holes, at least on the first side, before cutting the bottom off the tube. Failing those improvements, I'm at least going to drill only one hole, then temporary mount the new base alongside (as opposed to over) the sight and use a transfer punch to mark for the second, mount the part in my drill press vise and use a center drill to start the holes to prevent wandering. I may also do the drilling before cutting the profiles -- that'll save time if I have more problems drilling accurately, and improve my ability to transfer the sight ramp profile, for a neater appearance. Finally, I'm at least going to seek permission to make the next 45ยบ cut on the stock tube on a horizontal bandsaw we have at work -- that alone will save a half hour and a lot of muscle/tendon/joint aches (not to mention giving a cleaner cut).

I won't be waiting on money at this point; the only thing I still have to buy before mounting my BSA red dot is a pair of screws to hold the rail onto the base (should be under a dollar from the company I work for); I already have a tap set (cheap, but functional). Still, it's likely to be a couple weeks before I get caught back up to this point on the second try
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PostSubject: Re: Gun stuff from an industrial supply?   Sat Apr 21, 2012 6:02 pm

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Zeiss Ikon



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PostSubject: Re: Gun stuff from an industrial supply?   Mon May 14, 2012 12:34 am

Well, I'm about to start over for the third iteration. I'd gotten the front profile cut (combination of hacksaw and angle grinder), broke off a center drill trying to drill the first cross hole (for the screws that will go through the sight pin holes), offset the holes and successfully drilled both holes through the first side, close enough to perfect spacing that I was able to file a slight oval shape on one hole, at most about .010" out of round needed and parallel to the base (so wouldn't allow the sight to drift in elevation under recoil). I marked the holes on the second side with a transfer punch through the sight base, with a screw in one hole while I marked the other and vice versa, then drilled the second side -- and either the holes or the transfer punch (7/64" in a 3 mm hole is a few thousandths undersize, but not that loose) wandered by half the hole diameter. Crying or Very sad

This time, I'm going to check whether I can find the wave-set, fine-tooth blade that fits my bandsaw; as a woodworking saw, the blade speed is too high for best results cutting steel, but I've done it once before and if I keep the cut lubricated and don't feed too fast, it does work. I can cut the profiles on both ends with the bandsaw if this works, saving a huge amount of grinding and requiring hacksaw and grinder only to open the tube on the bottom. Then, I'll drill the holes on one side as before (scribed line parallel to top surface, scribed crossing lines set with my dial caliper for hole spacing, start with center drill and finish with #31), but drill the second side with the base mounted as I did when transfer punching -- but the drill running through the holes in the sight. The sides of the drill flutes won't cut enough to worry about, but the hole should guide the drill perfectly. The #31 is about .002" oversize for a perfect 3 mm, but I'll mike the pins and, if necessary, I can sand/stone down the flute diameter of a twist drill (I've got 10 I haven't used yet) in my lathe to avoid cutting the holes in the sight and base oversize -- or, I can use a 7/64" bit with a single wrap of tape on the flutes to center up, then redrill to size with the #31.
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Zeiss Ikon



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PostSubject: Re: Gun stuff from an industrial supply?   Wed May 16, 2012 5:47 pm

Sigh. Found the bandsaw blade I was looking for; despite being marked as "bimetal", which usually denotes a blade made to cut steel, it just makes a lot of noise when I try to cut a scrap from the rectangular tube with it.

Looking at the second attempt, however, it does look as if I could slot out the holes where they wandered and be okay; in both cases, the necessary slotting would be at right angles to the major recoil forces. I'll have some work time tomorrow, so I'll check pins vs. #31 drill for size, stone the flutes on a drill bit if needed, and redrill the second side holes through the rear sight pin holes. That should leave me ready to cut the rear profile (clearance for the sight adjuster to at least 500 yard setting), then drill and tap the top for my rail before mounting the red dot I already have (to test the mount before spending money on a scope). If the redrill works, I ought to have the mount ready to test (i.e. all cutting finished, but not polished and blued) before I can get my rifle back in service from the broken interrupter.
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Zeiss Ikon



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PostSubject: Re: Gun stuff from an industrial supply?   Thu May 17, 2012 9:16 pm

Well, I was right -- I was able to slot the holes that had wandered enough to get the screws in, and the slots are neither parallel to each other, nor to the barrel, nor to a pretty good guess on the direction of resultant forces from recoil acting on a scope mounted on top of the base. I used two files from a needle file set I bought literally decades ago (throwing away a tool is one of the more heinous sins -- a truth which has caused conflict with a couple wives), and test fitted many times along the way -- in the process noting that my particular rear sight is quite loose on the dovetail when the pins are out, with both vertical play and easy longitudinal movement (the pins, however, which are half a thousandth oversize for the holes, hold everything quite snugly). This might be of use if I don't like this mount and want to try mounting direct to the dovetail.

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I do find that the base is tilted down a little toward the front; I expect I'll have to shim the front end of my rail to get a zero at reasonable distance, but shim stock I've got. If I can find a way to level the bore without buying an expensive purpose-built tool, I may try to determine how much tilt I've got, to see if there's enough metal available on the top to grind out the slope. Failing that, I'll just have to mount my rail and red dot and boresight.
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PostSubject: Re: Gun stuff from an industrial supply?   Fri May 18, 2012 2:01 am

Lookin good. Smile Man that scope is gonna be up there pretty high.

I had a SVT 40 and I made a scope mount for the rear of it. It looked similar to this. I had one cross bolt holding it in place. After about 20 shots, that cross bolt was bent from the recoil. I think yours though, will hold up better.
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Zeiss Ikon



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PostSubject: Re: Gun stuff from an industrial supply?   Fri May 18, 2012 8:29 am

SilverTip wrote:
Lookin good. Smile Man that scope is gonna be up there pretty high.

I had a SVT 40 and I made a scope mount for the rear of it. It looked similar to this. I had one cross bolt holding it in place. After about 20 shots, that cross bolt was bent from the recoil. I think yours though, will hold up better.

Yep, I'll be using a "chin weld" with the original stock when I get the scope mounted. Easier on the neck, though; I get a crick bending my head down/forward enough to use the iron sights.

These screws aren't going to bend; they're encased in the sight or scope base full length. They might shear, if the recoil is bad enough (especially if the mount had some free motion, which as far as I can detect, it doesn't), but they won't bend.
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