Hi guys, thanks for tuning in to another video on ForgottenWeapons.com.
I'm Ian McCollum, I'm here today at the Royal Armouries and the National
Firearms Centre in Leeds, England, courtesy of ARES, Armament Research Services.
And today we're taking a look at a hand-cranked machine gun/grenade launcher sort of thing.
This is a Mark 18 Mod0. These were actually used in
surprisingly large numbers in the Vietnam War by US troops.
Now, this thing was pretty much obsolete as soon as it was introduced,
but it was actually still a pretty good weapon. It was pretty well liked,
it worked pretty reliably, it just had some ammunition issues. So let me get into that specifically.
When most people see like an automatic grenade launcher, what they expect is this.
This is the 40x53 cartridge. It is a high-pressure grenade cartridge.
But it's not suitable for things like underbarrel rifle grenade launchers,
because it is, in fact, too high pressure. Those underbarrel grenade launchers
need a much lower pressure cartridge in order to not explode and stay light enough to be easily portable.
So the cartridge that they use is this one. It's 40x46mm, so 7mm shorter than the high-pressure round.
This guy, this Mark 18, is designed around the low pressure
(it's actually what's called High-Low, where there's kind of an expansion chamber
inside the cartridge case, we don't need to get into the mechanics of this cartridge today),
but suffice to say it is the low pressure version of the 40mm grenade round. And this guy was designed for it.
And that's why it became obsolete very quickly is, right about the time this was being introduced,
the high pressure cartridges were being developed for this type of weapon.
Now the other thing that makes this really interesting is that,
well, the mechanical function of it. It is hand cranked, and it's a split breech.
I guarantee you you'll take one look at it and be quite surprised that it works
in the way that it does. I know I was.
Little bit of additional background though, development of this started in 1962,
it was patented in '64, and then the military ordered a total of 1,200 of them,
by 1968 orders and deliveries had ended.
They were primarily actually used by the Navy, and the Navy was the first service
branch to actually purchase them. The concept had been use by a two-man team,
kind of like the thing is set up right now, on a standard M2 tripod.
In reality, however, they tended to be primarily used on Navy patrol boats.
Part of the reason for this is this low-pressure grenade cartridge has a very short range.
Maximum effective range is maybe 400 yards with one of these cartridges and with a short barrel,
and this type of firing mechanism, which we'll get to in a moment,
effective range for this was probably more like 250 yards.
So on a patrol boat, where the goal was to break contact very quickly and get away
from something, that worked quite well. In an infantry role it was
probably going to ... have too short of an effective range to be all that usable.
Let's go ahead and take a look inside this. Let me show you how it works, cuz it's weird and different,
So the way this works mechanically is you've got one hand to control it
(it is kind of locked into a tripod right now).
... So we have a three position safety selector,
over here on the right is the loading position for actually putting a new belt into the weapon.
And then on the other side we have the safe and the fire positions.
So to change this you pull it back slightly and rotate it. In the safe position you can cycle the the weapon,
but the firing pin isn't triggered, or isn't tripped, so it won't fire.
And then of course in the fire position it makes a lot of noise and things explode.
Now the crazy part about this is that it is a split breech.
And there's a massive gap in between the two halves of the breech block.
So when I rotate the crank,
what's going on there is we have an upper spindle up there, and a lower spindle.
And they form the two halves of the chamber,
and so when they rotate together they bring in a cartridge case,
form up almost completely (there's actually a gap between the two which gives you space for the belt),
and they actually fire in that configuration.
So that's open,
that is the closed configuration, right there. And you still have this big old gap
which is pretty much lined up with the cartridge case. Now
the reason that this can actually function this way is because of this High-Low
internal mechanism in the cartridge case. The majority of the pressure of firing happens
really before the projectile actually leaves the case.
... In that way this kind of functions like a revolver cylinder gap,
where, yes, it's going to leak some pressure, but it's not going to be catastrophic.
In order to disassemble this, I have put the safety on the load position. I have the handle pretty much vertical,
and I'm going to take this big flagged lever and lift it up vertical.
And that unlocks the top,
of the mechanism, so I can
pull it
out ... and open. And now, ooh, we have all sorts of cool mechanical bits in here.
We can see the bottom spindle here, and you'll notice that it has a step in it.
That step is to accommodate the belt.
So the grenade cartridge is going to fit right there.
Peel it out. The belt
... used with this is actually an interesting piece of technology on its own.
This is not a cloth belt, but this is like those that
1960s super space-age sort of thing. This is Mylar reinforced Dacron,
effectively a cloth belt really. And we've got, it's kind of delaminating here, but
with the rounds fitted to the belt you can see the belt fits right into that step in the two
spindles. So when the top spindle closes over this, you have space for the belt.
When you fire this, the case actually remains in the belt, so you're gonna put a loaded belt in one side
and you're going to get a belt full of empty cartridge cases coming out the other side.
The belts were not totally reusable, you could get four to five
recyclings out of a belt before it was basically destroyed, and then you throw it away.
So, and honestly kind of like cloth belts in that regard, they're reusable, but not indefinitely reusable.
Alright, when I turn the handle (actually I have to hold this little safety out manually,
that's normally done by a piece in the top cover),
when I turn the handle you can see two separate things happening simultaneously.
At approximately the top and the bottom of the handle's travel, it's rotating this bottom spindle.
And then it's also running this lever back and forth.
Now this lever connects to an arm on the top, and this directly controls the top spindle.
So it forces the two to synchronise.
Obviously they have to be synchronised so that the top and bottom line up,
so you have space for a cartridge inside.
If we look in the bottom here, you can see a set of gear teeth that are
responsible for all of that rotation. Now if I move this to the fire position,
you can hear that snapping, that is the firing pin tripping, which is right here.
Comes back, released. And that's also controlled by the same cam system,
so the firing occurs at roughly the rearward
and forward positions of the handle.
Right here we have the hook that interfaces with the lever on the bottom assembly.
As this cycles backward and forward, it rotates the top spindle.
And I have to leave it where it is, so that it's synchronised when I close the whole unit back up.
But that is how the top spindle is matched.
The practical rate of fire of this was probably something like 100 to 200 rounds per minute.
One of the user reports was that if you tried to run it really too fast, it got a bit ragged.
You kind of wanted to control the rate of fire on it to make sure it continued to run smoothly.
That said, in testing it was a remarkably reliable system, that was able to go something like 5,000 rounds
on average ... between stoppages ... So really quite an effective weapon, if a bit
simplistic, and low pressure, and low power for its period.
Where you did have the potential for stoppages from well,
largely probably from worn belts or mishandling, trying to run the thing too fast, or ...
Typically crank fire guns are always susceptible to ... jerky motions by the shooter.
...You want to keep a nice steady pace on the handle and not speed up and slow down
jerkily in order to run the gun reliably.
The sights on the Mark 18 Mod0 are this sort of, they kind of look like aircraft style spider sights.
You'll notice that the rear sight is elevated way above the front. That's because these grenades have a very
rainbow-like trajectory. Short range, high angle of fire. So that's your sighting system.
There's of course a data plate. These are the markings on the gun.
Interesting to point out this is a Gun, Rapid Fire, 40mm. This was before they were using the designation
grenade launcher or grenade machine gun on something like this.
This particular one is actually a very early one, number 82,
manufactured in '66 by the Honeywell corporation.
Total weight as you can also see there, 27 pounds, not including the tripod.
Thank you guys for tuning in to watch.
We haven't done a whole lot of grenade launchers, but hopefully that will be changing
as part of our on-going series with the National Firearms Centre and ARES.
There's some really cool stuff in this type of firearm.
So if you enjoy that, make sure to check out the ARES blog post that goes along with this video.
They'll have a bunch of high-res pictures of the inside and the outside of this Mark 18 Mod0.
If you would like to see it in person, along with a wealth of other light grenade launchers and
automatic cannons and that sort of ordnance, get in touch with the Royal Armouries.
The NFC collection is not open to the public, but it is available
by appointment to legitimate small arms researchers.
Thanks for watching.