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Mosin-Nagant Factory Pressure Test Rifle


Hi guys! Thanks for tuning in to another video on ForgottenWeapons.com I’m Ian McCollum and I’m here today at the Rock Island Auction Company where we are going to address two separate questions. One of them is “Why is there a weird thing growing out of this Mosin-Nagant receiver?” And the other is “How did they measure chamber pressure a hundred years ago, before they had computers or like fancy electronic equipment to work with?” Well, THIS is how. Let me show you. The answer to “Why is there a thing growing out of my Mosin?” is, of course, that it’s a PRESSURE TESTING rifle. The answer to “How do you determine pressure?” is you take a piece of solid copper and you see how much it squishes when you expose it to chamber pressure. This should be a good reminder to folks of just HOW much pressure is in that rifle’s chamber when you pull the trigger on a live cartridge. You know, this is “only” a .30 caliber cartridge and You’re gonna measure its pressure by physically squishing this thing down a measurable amount. So, that’s a solid block of copper – that’s no mean feat. Now, the way this works is… Let’s see… Let’s actually just start by taking this out start from the ground up. So, what they did is they took a standard Mosin-Nagant (and this is a beautiful one, by the way) And then they added this ring around the receiver. (In fact, it’s actually in front of the receiver – it’s just around the base of the chamber, which is where your chamber pressure is going to be highest) They added this ring because they also went and drilled a hole straight into the chamber. So, you can see that center hole, you know, that goes right open into the chamber. Then… You’re going to have this device. This guy screws into that pressure ring, and then we’ve got a second piece here that we raise up [Placeholder music] And then there is a little piston right here. That piston travels inside this plug… Now, the purpose of this plug and this pressure ring is so that… When you fire the rifle with a hole drilled in the chamber, that pressure is going to be exposed to the center, Where it’s going to push this piston upwards. This threading is thick enough that it will not blow out this whole unit. *That’s* what that’s there for. Now you’re going to take your piece of copper. Your calibrated specifically sized piece of copper. It’s in there… Open it up a little bit more… There we go. We’ll put the piston all the way down at the bottom and then this guy sits right in there, and I’m just going to tighten that down Now we have our piece of our copper block sandwiched between this immovable bit at the top And this movable piston at the bottom And then this gets threaded into that pressure ring. (You don’t have to actually take this out to put in one of those copper slugs) So, we’ll tighten it down to there… I can leave it there so you can see… And then, when you fire, this piston’s gonna get pushed up; that copper plug is going to get squished down, So it’ll get shorter in length and wider in diameter – you then measure the change in dimension of the copper And that translates into a unit of measurement which is… Not, I mean, kind of obviously, it is actually called “copper units of pressure”. So you will see, if you look up, like, old handloading databases or old information on cartridges… You’ll see chamber pressure described in copper units of pressure and then typically also in psi. And… People say you’ll find references that say that there is no conversion factor between copper units of pressure and psi – And that’s because this really isn’t an actual direct measure of pressure. It’s a secondary measure of pressure. The pressure is performing an action and then you’re measuring the *results* of that action. So that’s why you can’t take some numerical constant and convert from psi to CUP. Now there’s one other element here that’s important, And that is… Well… What if I just want to, you know, do some other test firing? Like, make sure that a cartridge functions in this rifle? Or measure muzzle velocity without venting gas into this thing? Well, that we have a *second* plug. This one is solid and if you look up close at it, you’ll see that it’s actually curved (right there) and that matches the curvature of the chamber. So, this guy is serialized… One… Uhh, no, that’s a date – 1914. It is serialized *over there*… 4797. It is custom made to fit *specifically* this rifle, Because you can thread this into there. (That hole is for a bar, so you can tighten it all the way down) And when you do tighten it all the way in, that curved section on the very bottom nicely seals up the top of the chamber In line with all the rest of the curved surface of the chamber. So, with this plug in place, you can now fire a normal cartridge without venting gas out your open hole in the chamber. There are a couple other things that I want to show you. Well, we can take a look up close at this rifle. They have number there – 4797. They put that number there, presumably because this goes right across the top of the chamber (where the original serial number was). There’s a really nice crisp stock cartouche in this rifle, And it’s the sort of thing you don’t often see in a Mosin-Nagant, because most Mosin-Nagants went through, you know, All of World War one (if they had been made that early) and then World War two. Well, this one didn’t, because it’s a chamber, you know, pressure test rifle. Bolt is also numbered – 4797. They did go ahead and add that serial number back on the side of the the chamber (right there). Pressure testing versions of rifles are around like this for a lot of different types of rifle. It’s not just Mosin-Nagants. This certainly was not something that was unique to Russia and the Mosin-Nagant development. You’ll find these for a bunch of other [rifles]. What’s funny is you’ll find these for a bunch of other types of rifle. Most often – rifles that were made by factories that were Occupied by invading armies, because stuff like this often ends up being a cool souvenir that some soldier brings home. So, for example, I’ve seen pictures of Arasaka pressure test rifles (which isn’t all that surprising). Those things would get picked up as souvenirs in 1945 and 46 – the years, you know, when the US was occupying the Japanese Arsenals. But really, every major factory that did military rifles would put together some guns like this, So that they could properly develop ammunition. So, it’s really cool to see one like this that actually has all of the equipment with it. Usually bits like the actual pressure testing anvil and the, you know, the firing plug… Usually you don’t find those most often. You’ll find a rifle that has, you know, there’s pressure ring on it or whatever other alteration was made by some of the other factories. Pretty neat to find all the equipment together and, thus, be able to see exactly how it worked. So, if you would be interested in adding this to your own collection, There’s always kind of oddball guns, where it’s, like,.. You’re not actually gonna shoot this thing, because there’s a hole in the receiver And you’re probably not going to try and set up your own, you know, Ammunition Testing Service to figure out pressures on Mosin-Nagant cartridges, so… These things. And yet these things are really quite scarce and really cool. But there’s always that kind of… You know, “for the collector who has everything else” sort of deal. So, if that might be you, take a look at the description text below – you’ll find a link there to ForgottenWeapons.com From there you can click over to Rock Island’s catalog page on this guy That will show you all of their pictures (the high-res pictures), their description, their list of all the bits that come with it, As well as their price estimate and everything else you might want to know about it. Thanks for watching!

100 thoughts on “Mosin-Nagant Factory Pressure Test Rifle

  1. If the testing apparatus is still functional, maybe set up a special one-time Patreon deal so you can put a bid in for it (assuming you don't plan to anyway) so we can get a video of it being used. I'd chip a few $ towards that.

  2. I imagine a function dependent on some basic properties of the piston could allow one to convert the two units (at least theoretically to a reasonable degree of precision). Very interesting, reminds me of the weight – mass distinction except with a 'gravitational constant' which is determined by a highly variable man-made device.

  3. Everyone seems interested in the prospect of seeing this rifle test fired and the copper gauge deformed. I'm simply interested to see how high the hammer price will be on such a rare item

  4. Seeing this you kinda have to wonder how many tests they did before to rely on this copper squishing device. I guess being a gunsmith was a pretty adventurous job back then.

  5. So when the cartridge fired I am assuming that the 54000PSI chamber pressure would have blown a neat hole in the side of the case adjacent to the hole in the chamber and leave small disc of brass in the space below the piston? Otherwise there would be a bulge of brass protruding into the piston hole which would prevent extraction of the fired case or is the distance the brass moves against the piston so small that it just springs back?

  6. I have one. Its a wonderful rifle that can take a beating, drop a bear, and fantastic coyote rifle. Best part is they only cost like 100 bucks and the ammo is usually about 10 bucks a box of 20

  7. I would strongly suggest these for anyone just getting into hunting for the first time or into range shooting. Its a fantastic rifle that doesnt break the bank

  8. I don't know what I'm talking about, but that won't stop me from offering an opinion. It seems to me that the reason that you would not be able to convert directly from cup to kpsi isn't because the copper movement is an "indirect measure." After all, all measurements are "indirect" in some fashion or another. I think the issue is that the amount by which the copper moves will not be a function of peak pressure, but rather a function of the amount of time at pressure.

    A ductile metal like copper will begin to deform when the stress exceeds a certain critical value called, if memory serves, the "yield stress." After that, it will basically move like a viscous fluid. The copper will continue to deform as long as the pressure remains above the yield stress, so you will get more deformation either by raising the pressure or by sustaining the pressure for longer.

    Think about the difference between compressing a spring and squishing a piece of play-doh. Below the yield stress, the copper block acts like a (very stiff) spring. Above the yield stress, it acts like play-doh.

    To get a true pressure measurement, you need a transducer that behaves like a spring over the entire pressure range.

  9. As a reloader I know what CUP is and have that info in some of my older manuals, but I've never seen a pressure test rifle . So this is a really cool video to watch . In recent reloading manuals PSI is used , and there is information stating the barrel used for load development of each cartridge before the various bullet weights and charges of powder used . Often times the barrel will be a certain manufacture , length and twist rate . But sometimes the barrel used is listed as "test barrel '. A knowledgeable shooter and reloader should inspect the fired brass for signs of overpressure . These are , but not limited to , primers showing signs of backing out of the pocket , primer cratering , primer flattening , excessive case stretch , and such . Interesting story , I was new to reloading and told a relative I could use the spent brass from his 30-30 to reload better than factory ammo . When I received some brass he had recently shot I gave them an inspection before depriming . The primers were set back from the pocket a few thousands of an inch were a bit flattened , and were starting to crater . I asked him how his rifle was shooting . He said as accurately as ever , but the recoil seemed harder . I told him his rifle was shooting too high a pressure . Over the years he cleaned the powder residue from his bore and chamber, but never cleaned for copper fouling . After a thorough cleaning of copper buildup the rifle shot factory ammo with no signs of overpressure , but accuracy was terrible . My handloads shot equally poor groups . Years of improper cleaning had damaged the the rifling just forward of the chamber . The fouling was allowing the bullet into the rifling straight but slowing it's release from the case . Y'all Take note . Clean your guns of powder residue and metal fouling . And if your spent brass , especially the primers , look wonky , have the gun checked out before shooting it anymore . Peace , Out !

  10. Last time I checked, Winchester was still listing the pressure for the Ranger T-Series 127 gr. +P+ (RA9TA) in Copper Units of Pressure. On the last box I bought, they had it listed as 42,000 C.U.P. One source I found claimed this is a crossover point, where C.U.P. and PS I are in general agreement. Not sure if this is true, but–side note–that stuff sure beat the hell out of my gun, and extra stiff springs didn’t help!

    I’ve always been interested in C.U.P. If I loaded for 7.62x54r, I would be sorely tempted to use this collector’s item for its intended purpose.

  11. I mean so long as you know the Young's modulus of the copper sample then you can calculate the force applied. The force applied divided by the surface area of the chamber should be your chamber pressure

  12. The stuff I learn. I'll join your patreon. I've never done that before, but the world would be lesser without Forgotten Weapons

  13. Best oddball rifle seen in person is a 1903 Springfield rifle converted to a .45auto test pistol. On display at Springfield Armory NHS.

  14. I just came across your gun smithing channel how come you dont do those type videos anymore? We need more good gun smithing videos like mark from c&r

  15. Why do they do this? To check their manufacturing tolerances have not strayed too much over time?
    The gun is already in mass production, so I assume they're not doing it to re-design the gun, but to tweak their manufacturing

  16. Very cool gun. I never thought about how they measured chamber pressure in those times.
    What would have been really cool, besides seeing the measurement process of course, would have been a second one of those copper pieces from after the test to get a feeling about how much it shortens. But I'm pretty sure you just didn't have one on hand.

  17. Of course you can convert,you take the stress deformation graph of copper,you put the permanent deformation ofthe copper on x and you go up with a line of the same inclination of elastic deformation ,when the line intersect the copper graph thats the pressure on the copper,you multiply that for (Area coppercylinder)/(area piston) and you obtain the pressure inside the chamber

  18. Not sure what's more exciting, squishing the copper plug, or the threads that hold that force and more. Would be cool to have a dial on the top too…

  19. """Although no accurate conversion formulas are possible, for converting between true pressures and crusher indicated pressures, linearized approximation conversion equations do exist over narrow ranges of pressures for estimating piezo pressure readings given crusher pressures.""", Wikipedia 'Copper Units of Pressure'.

    This means, that b/c the copper plug's deformation is not measured over time, they can only get a single number for the pressure and it's influenced by some response curve.

    The modern transducer creates that nice pressure trace over time. You can just pick off peak, or whatever.

    It's fun to think about the trace of, the force vs compression of a copper plug. Since it's compressible, it's non-linear; there's a curve in that trace. You're not completely done, bc that curve is (hopefully) a linear function and you can fit to it and get a good conversion if you know a lot of facts about the setup you are testing. You'll have uncertainty with every conversion factor though, so it's not easy.

    I made most of that up…but i think it's a good guess.

  20. As someone who works in an ammunition factory I find this very intriguing. I would very much like to own this if only I had the money to do so.

  21. Very interesting rifle for pressure testing. Thanks for showing this interesting rifle Sir an have a Happy thanksgiving.

  22. I love this, it is so much more palpable and aesthetic than electronic measurement. Rule of thumb: Everything was cooler in the past except when you got sick or belonged to the lower class.

  23. For some reason I'm much more drawn to the old school of engineering to the modern day CNC and 3d printing era, I could watch things like this all day

  24. They were capable of fine machining in Tsar Russia… Communism flawed perceptions, curbed motivations and ideologized "truth".

  25. This makes me think of an old gunsmith i knew. His method of making the hottest loads he could was to keep loading hotter and hotter till the primer would push then he just backed the load down slightly. I was always amazed he never fucked himself up. He may have loaded ammo like an idiot and looked like a troll but he was a good gunsmith.

  26. Would there be case wall covering the hole at the base of the chamber? I mean, if the case strength is also accounted for in this method, and the cylinder is measurably squished, the case would be ruptured or noticeably deformed, right?

  27. "…and then this guy sits right in there…"
    Not gun Jesus, that's probably Browning, Stoner, Kalashnikov, or another gun smith.
    Ian is Gun Bob Ross

  28. Copper Crushers, as the copper pistons are know were a common way of measuring the in chamber pressure of many rifles. Normally what would happen would that a manufacturer of these 'crusher's' (which came in rods and balls) would sell them as lots with pressure tables (a tarage table), as Ian mentioned, one you have fired your round you would measure the amount of compression on the rod and ball and compare it to your table to give you a pressure measurement. This system had been around since the early 50's and was uses world wide in small arms, even though it began life which large calibre (i.e. artillery pieces).
    As of 1977 Abderdeen Test Centre delcared that the Copper Crusher Method was no longer suitable for NATO purposes as it could not be measured precisely, therefore nowadays most NATO countries (and many non NATO countries), use Piezoeletric sensors which are quartz based sensors which can provide measurements with accuracy to normally 0.5%. (Depending on how well the equipment has been maintained, whether it is within it's calibration spec and the DAQ system it is attached too is operated by a competent user).
    Oddly enough you still see copper crushers being used in and around the middle east and normally on shotgun cartridge testing mainly out of habit and that Piezoelectric sensors can be expensive (read approx $2-3k per sensor).

  29. I don't understand how it's "impossible" to convert copper unites to psi. psi itself is, of course, also measured by measuring its effect on something else.

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