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!