so a good friend of mine wants to put a scope on his mosin. He wants the modern reproduction of the original PU scope. we're still trying to locate all of the parts he needs. we're also looking for a really good, in depth write up on not only what needs to be done, but the proper way to do so.
we know the receiver needs to be drilled and tapped, but how exactly do we line up the mount so that the scope is exactly where it needs to be over the bore? is there a trick to it, or will it require some tedious measuring and remeasuring? even though his rifle isn't anything special, its a nice arsenal refinish that we don't want to "bubba" up.
any help on locating the parts and installing them would be greatly appreciated.
on a related note, how are the 91/30s that AIM is selling? i've been thinking of picking one up for myself, but i'm a little reluctant to buy a gun sight unseen.
I would get an ex-sniper if he wants to put a scope on it. That way you already know where the holes are and you aren't "bubba-ing" anything.
AIM should be good to go, never read anything negative on here about them. If you want a specific characteristic, just do a hand select option and put what you want in the notes when you order.
I apologize for this being so long, but it's not something you can really cover in one paragraph! I also apologize, up front, for any typos. It's late, I'm tired and I didn't take the time to proof read everything.
Okay, so let's assume your friend has picked up an ex-sniper. First off, I should say that they're really not that hard to find, especially an Izhevsk PU dated '43/'44. So, look around for one that has an excellent bore. There are plenty of them out there and the price can be the same, or only a little more than a standard 91/30. Plus, you have the benefit of having a rifle that has the sniper history. In any case, get the rifle and test fire it to make sure it's going to be a good shooter and to zero the iron sights. Even if it shoots high or low, that's not a problem, so long as you take note of where it's hitting. You'll need this info later, when it's time to zero the scope.
Next, you need to determine what the hole spacing is between the main screw holes, center to center. Usually, they will be one of three spacings; 53.5mm, 54.5mm, or 55.5mm. Once you have determined that, you can order a mount/base combo (and even the scope with it, if you wish), from Accumounts.com. They will have a setup with the base that has one of those spacings. You just need to specify which one. Also, should you come up with an ex-sniper that has an odd spacing, they sell blank bases that you can drill out to match your gun. I have yet to see it happen that way, but it's not impossible.
From there, you need to remove the old screws in the receiver. They are usually welded in. What I normally do is use a center punch to mark the centers of the screws, from the inside of the receiver. BE SURE THAT EVERYTHING IS LEVEL, AT ALL TIMES! It may be required to flatten the tip of the screw, as some of them come to a slight point, before you center punch them, so that you get it well centered, without slipping off to one side. Then, if I got them perfectly center punched, use a 6mm drill bit (one comes with the Accumounts kit) in a drill press to drill them out, from the inside. If, by chance, you did not get them punched on center, you can use a smaller diameter bit and gradually work the holes with progressively bigger bits, until you get the screw out, being careful not to destroy the existing threads. Usually, once you get the screws drilled out, the remainder of the threads just fall out. If the weld is deep enough, or the remnants of the screw threads aren't coming out, you can chase the hole with the tap (also supplied in the Accumounts kit, but be careful, because they're not the strongest taps in the world!). The key to remember in all of this, is to go slow. Use low RPMs on the drill and plenty of cutting oil as you go. I usually apply a few drops every few seconds. Just take your time. The same goes with tapping the holes. Use plenty of oil and just go a little bit at a time. If you start to feel real resistance, STOP! You need to back it off and clean out the chunks. This is extremely important and you can break a tap faster than you can say "This is getting hard to.....shit!" (don't ask how I know this!).
Once you have the screw holes tapped and the screws will go in cleanly, screw the base on. Then, use some masking tape or a pencil to outline the front and back of the mount. Remove the base from the receiver. Set the action back in the stock and mark the stock at the tape lines, where your relief cut is going to be for the base (add about 2mm to all of your cut lines on the stock, to give a little room for contraction/expansion of the wood and for recoil and action tension). Also, put some more tape at the horizontal stock line, to mark where the stock ends on the receiver, in front of, as well as behind, the taped off base area. You can also use a pencil to draw this line. Either way, you need to know how high the stock goes up on the receiver. Now, remove the action from the stock again and rest the base in place (you don't necessarily have to screw it back on yet, but you want the holes aligned. Measure the distance from the stock line that you just made on the receiver, to the bottom of the base. Also, measure the outline of the lower elevation screw tab. Use these measurements (again, adding a couple mm for clearance) to complete the outline of the relief cut on the stock. From there, you can use a razor to start scoring the lines in the stock. I like to use a hobby saw (fits in an X-acto knife) to cut out the chunk of wood for the scope base. Towards the front of the cut, it may be required to hit it from the back side, to cut all the way through. A cut-off wheel in a Dremel tool works nicely. It shouldn't take too much, though, as you'll likely be able to get most of the way through with the small saw blade. Later, once your base is mounted, you can check the fit and trim if required.
For the pins, the same principles apply, as were used on the screw holes. Go slow and use oil to drill the holes. I would start, however, by using the base as a guide to center punch your holes and get them started. Be sure you have the screws tightened down firmly, so that the base is in it's final position to get the pins in the right spots. It's possible that the pins may not perfectly align with the originals. However, I have yet to have any problems from this. If you can find the orignal pin holes and get them to align, that's great. If not, just go by using your base. I would not drill all the way through the receiver to install the pins, unless you have one where the original pins are aligned with your holes AND they were drilled all the way through, to begin with. Usually, about 4-5mm deep is good enough.
The tolerance of the pins in the holes has to be tight, so a loose base will throw off the alignment. It may be necessary to turn down the diameter of the pins to get them to fit properly into either the receiver, the base, or both. You want them tight to the point that you will have to TAP them in with a hammer. So, what I normally do, is to chuck the pin in the press and turn it against a file, a little at a time, stopping repeatedly to check the fit. It may be necessary to have one end of the pin smaller than the other, to match the holes in either the receiver or base. The difference in size will be miniscule, but required.
Once the pins are in place, tighten the screws the best you can and check the fit of everything. If you've done it right, it should be good to go. Now, you want to take note of where the smaller keeper screws will line up on the main screw heads and mark the heads. Remove the screws and use a mill bit to mill out the semi-circles where the keeper screws will go. Apply some loc-tite to the main screws and put them back in place, then screw in the keeper screws and you are almost done.
After this, you'll want to attach the mount/scope to the base. Try to get both of the elevation screws turned in so that there's an equal amount of space between the upper and lower edges of the mount, at the rear. Tighten the large thumb screw. The first think you'll want to check for, is that the scope is centered over the rifle and that the reticle is level. If not, there are ways to shim it (or/also loosen the rings and twist the scope to level, if needed), but we'll get to that in a bit, as you may have to shim for a proper zero, as well. But, for now, just take note of the scopes alignment over the rifle. Now, put the rifle in a solid rest and get the iron sights aligned on a target that's approximately 100 meters away. Check the scope to compare sight pictures and see what kind of adjustments need to be made. If it's only off by a very small amount, you can just use the elevation and windage turrets to make the corrections and get it as close as you can to what the POA should be. At this point, there are a lot of directions this could go. You need to make sure everything is tightened down and go out to test fire the rifle. It shouldn't take too long to figure out any alignment, elevation or zero issues. If the reticle is fairly well entered in the FOV of the scope, but you are shooting way left, you may need to file down the "pads" on the back/rear area of the mount, where it contacts the scope base. Before doing this, however, I would be sure that any windage needed cannot be attained by a simple scope adjustment. If you have one of the scopes where the reticle does not move in the FOV, I would put it at mechanical zero and adjust the mount from there, to get it as close as you can to zero, before going back to adjust with the turrets. If, however, you have an original PU scope, or one that functions like an original, where the reticle moves within the FOV, you may be able to zero the scope within the FOV, but you may find that it's off to one side, or high/low. If this is a small amount, it's no big deal, if it's way off to one side, you will want to adjust the mount by either filing the pads, or shimming under them with a thin plate of metal, until you get it to an acceptable sight picture. Also, with the original style scopes, you want to keep in mind that, to dial up for long shots, the reticle is going to move down in the FOV. So, unless you do all of your shooting within a few hundred yards, you may want to zero the scope so that the reticle is a little higher than center in the FOV. This way, if you want to dial up a 1000 yard shot, you'll have plenty of elevation adjustment in the scope to do so. You can also use the two elevation screws at the back of the base, to make your base elevation corrections, before using the reticle to fine tune the zero. Once you have them set where you want them, screw them in tight and leave them. The Russians would usually stake the screws into place, to be sure they wouldn't move.
Going back to the possible misalignment of the mount/scope over the bore axis; If you find that the scope is off to one side and not centered over the bore, you can usually shim it in a similar fashion as described above, for the zeroing procedure. However, if the mount also requires a shim to get the scope zeroed, you'll have to find a combination that works for both. This is extremely unlikely with a new mount, though. The only problems I've had with this issue were on an original mount that had been heavily ground, so the scope was offset slightly to the left of the bore axis. It took a bit of work, but I got it centered and with a centered reticle zero. If you're using a new mount that has not had the pads ground, this most likely won't be a concern.
Now, if you were using a rifle that was not an ex-sniper (hypothetically, because I wouldn't condone such a thing), you would not have to worry about the hole spacing, the welded screw holes or existing pins. You would simply try to align the base to the bore's centerline and work from there. If you've got it parallel to the bore, you should be able to make up any difference with the elevation screws and the elevation turret on the scope, without any issues.
If I missed anything or if this is as clear as mud, I apologize. I'm always willing to answer questions, though. So, feel free to fire away, or IM me.
I forgot to add; you'll also need a bent bolt, of course. There are some available out there, both in completed parts, as well as guys who perform the service on your existing bolt body. I have a favorite "go-to" guy; Mike Battersby at Mosin Parts, LLC. I've seen/used them all and his have been the best, so far. His prices are competitive and turn around times are very short (No way am I waiting 3-5 months to have a bolt done when he can do four of them in two weeks for me!).
Thanks for all of the information guys, especially you AKJP. that's exactly the kind of write up we've been looking for.
i'll pass the information along too him and see what he says.
Thanks AKJP . I have an ex -sniper and have been wondering about bringing it back