Hi guys, thanks for tuning in to another video on ForgottenWeapons.com.
I'm Ian McCollum, and today we're going to take a look
at the M79 40mm grenade launcher.
This was an outgrowth of development after World War Two,
largely looking to replace the bazooka
with something that was both more portable,
more accurate, and more effective.
The bazooka was not bad for what it was originally
designed for, but it left a lot of things to be desired.
It gave a whole lot of evidence of firing when you touched one of those rockets off,
it became very obvious where it was coming from.
It wasn't particularly accurate.
And ... it was kind of a big, bulky thing to carry around,
both the launcher and its ammunition.
And in the Korean War the military started looking for other ways to deliver explosives
to things like enemy bunkers or strong points.
If you didn't have a tank, or you didn't have a guy with a bazooka,
... the US Army didn't have a whole lot of good options for how to attack a target like that.
So, there are two parts to the M79.
The M79 itself is a very simple weapon, we'll take a look at it up close in just a moment.
But really the important developmental point with this system
was the ammunition, not the gun itself.
So we're going to talk about the ammunition for a moment.
It is the 40x46mm grenade, commonly called like a high-low system, or a low pressure grenade.
And the idea is you're looking for something with a relatively limited range.
This is a 350 to 400 yard effective range weapon, and it's very accurate within that range.
But you're not looking for artillery, you're not trying to launch something 1,800 metres away.
This is for relatively close targets that are being engaged by infantry with rifles.
And if you keep the range relatively short you can keep the recoil down,
and allow a large projectile like a 40mm grenade
to be fired from the shoulder without too much problem.
It also allows you to keep the weight of the weapon down.
Ultimately the M79 would have an aluminium barrel,
you couldn't do that with a really high pressure round.
So there are two parts going on here, first off we have the projectile.
This was developed by the US arsenal system
in conjunction with private industry in the 1950s.
... In 1953 they had the development of what was called Project Niblick,
which was named after a golf club,
because the original analogue for the grenade in some of the very first testing was a golf ball,
which is about the size of a 40mm grenade, the actual projectile part.
And ... the very first guys who came up with this were kind of thinking like,
"OK, if we launch a low-velocity, round, golf ball sized grenade,
we can do this relatively accurately."
And they took basically a piece of pipe with a spring in it, and some holes drilled across the side,
and they dropped a golf ball in, pinned it down,
held this tube up, pulled the pin out, launched the golf ball.
And by the way, they did this experiment in the central atrium park
of the Pentagon building of all places.
And the result was like, "Huh, this works pretty well, let's develop this."
So the early development focused on creating a projectile
that was cheap and efficient to manufacture,
that would have an effective fragmentation.
And what they ended up doing was basically creating sort of a pre-fragmented printed casing
to the grenade that would have about a 5 metre lethal radius when it exploded.
And it would create hundreds of small
(we're talking just a couple millimetres at the small end),
a couple hundred small fragments when it exploded.
And they ... figured out a way to do that easily and efficiently
which is important for making a system that's going to be reliable,
and repeatable, and accurate, and - et cetera.
The Honeywell Corporation came up with the fuse for the thing.
It did have a safety fuse so ... the grenades will not detonate immediately in the barrel
or like if you drop them.
It's based on rotation (these have rifled barrels),
so the projectile has to travel about 30 metres before it's armed.
Honeywell came up with a fusing system that was, again, very reliable,
but also very cheap and effective.
And you put those together: now you've got a projectile to work with.
And the next question is how do you launch it?
Well, it doesn't need to go very fast, muzzle velocity is about 250 feet per second.
These are very high looping sort of trajectories to get out to 400 yards.
The problem is when they started experimenting with low pressure ... firing,
they had trouble getting clean and consistent powder burns.
And you can see that in firearms hand loading.
If you load too light of a powder charge
you get incomplete burning, your velocity varies wildly.
... Especially velocity on a weapon like this that has a very low muzzle velocity in the first place,
just a little bit of change in muzzle velocity will throw off your sights and your accuracy.
Because the projectile will go quite a lot farther or shorter than it's supposed to.
So they need a way to get consistent powder burn.
And what they turn to is a system developed by Rheinmetall during World War Two
for an 8cm anti-tank weapon where they had a similar set of requirements.
They wanted a light weapon, they didn't need that high of a muzzle velocity
because they were firing a hollow charge projectile, but it had to burn consistently.
And so what Rheinmetall came up with was this dual-pressure system.
Where basically you have a charge of rifle-like powder, fast burning gunpowder,
in a small contained section of the cartridge.
And it burns, and it burns up at a very high pressure,
and it then basically breaks a seal and bleeds into the rest of the cartridge case.
Which sort of ... frankly it acts like a suppressor, sort of.
It acts as a buffer, it allows the volume to go up which means the pressure comes down.
But you've already accomplished a nice complete clean burn of your powder,
so you now have a very consistent pressure being generated by the cartridge.
But outside of the cartridge itself ... you only have to hold a relatively low pressure.
So in the case of the 40mm, the high pressure section is about 35,000 psi,
... pistols are 20-25,000, rifles are more like 45-50,000.
So we're talking ... this is a substantial standard firearm sort of pressure.
However, that breaks out into the rest of the 46mm cartridge case,
and the pressure that the firearm actually has to contain drops to about 3,000 psi.
And that's what allows it to be lightweight, use an aluminium barrel,
and it generates this relatively low muzzle velocity of about 250 feet per second.
But it does it consistently and accurately.
So, when you put all that together, you get a really effective cartridge.
Now with that cartridge there would be a whole bunch of experimentation.
Springfield spent a number of years working on grenade launching solutions for the M1.
It didn't really go anywhere.
They had multi-barrel versions, they had harmonica magazine versions,
they had pump action versions, they had a whole bunch of different stuff.
And ultimately a lot of these experimental launchers had reliability problems.
They were too complicated, they were trying to do too much.
And it was apparently a guy named Roy Rayle, who by the way wrote a very interesting book called
"Random Shots: Episodes in the Life of a Weapons Developer", which I reviewed a while back.
You can check out that video, and if you're interested in this
definitely check out his book. It's cheap and easily accessible on Amazon.
He came up with this notion of like, "Let's simplify this down,
let's go with like a good old-fashioned break-action shotgun,
and just make a single-shot launcher."
And that developed into the M79.
So let's take a look at it, and we'll talk about then where it went.
This is a really simple weapon, and there's not a whole lot that we need to take a look at here.
Patterned on a break-action shotgun, we've got an opening lever here on top.
Note that we have a little pin here that is going to
keep this lever in the open position until I close the barrel again.
And that lever itself slides into this slot, and that's what holds the barrel assembly down.
This is spring-loaded, so it will assist in opening, not a whole lot, but a little bit.
We have a spring-loaded extractor right here to help pull the empty case out.
This is just single loaded, you pop it open, slide a shell in,
close it, and you're ready to fire.
We have a safety here on the back on the tang, just like a shotgun.
These were developed with a winter trigger guard.
So we have a little spring-loaded catch here,
push it in, and you can rotate the trigger guard down and out of the way.
Remember that a big part of the motive or inspiration for this weapon came from the Korean War.
Korea was very cold, Vietnam not so much, but you've got a winter trigger in there.
Probably the most complex part of the whole gun is the sighting system here.
So this is your rear sight, that's your front sight, and they're both mounted way up on the barrel
because this cartridge has such a low muzzle velocity and such a high arcing trajectory.
We have a battle sight zero, right here, that is 100 yards.
And then we have this whole upper leaf.
Now, you'll flip this up to use it. But because this is big and potentially floppy,
they didn't want it bouncing around and getting caught on stuff,
so there's actually a locking catch right here.
If I push this button down, that frees me to rotate the sight
and it will lock in the up position or the down position.
I do have windage adjustment right here, click adjustable.
For long range use we have this second rear sight notch.
This is a nice calibrated tower, it starts ... at 100 and goes up to 375.
I apologise it's a little hard to read there.
There is a micrometer dial here for very fine adjustments.
For gross adjustment you push this button in (this one's a little sticky),
and then you can just slide the thing up and down.
And if you don't want that to happen, if you want to lock it in place,
you can screw this in to tighten it.
... There we go. And now no spring and this is locked in position there,
so you can only use the micrometer adjustment for fine tuning it.
The front sight looks very much like an M1 Garand front sight,
although the front sight post is slightly different in shape.
It's a little bit of a shark fin style there instead of just a flat blade.
That's pretty much it for the technical side of the M79.
The barrel is rifled, so a 14 inch barrel.
Of course I should mention the stock here, this has a weird shape to it
because the gun is generally going to be fired at a relatively sharp upward angle, unlike a rifle.
So your cheek rest, your comb, is going to be necessarily of a bit of a different shape.
There is sort of a semi-pistol grip to the grip, but that's it.
So Roy Rayle's single-shot idea became the XM-79,
it was formally type classified as M79 and adopted by the US Army in December of 1960.
It would take a couple years to get into full production.
Of course there wasn't a huge need for it immediately in 1960,
but the Vietnam War would kick off and US involvement would ramp up quickly.
And by 1965 this was in full-scale production.
They would ultimately make about 350,000 of these "bloop tubes" as they are called,
or M79 40mm launchers.
Although they almost immediately started working on its replacement.
... This was a fantastic weapon, it was very well liked, it was very accurate.
The guys who practiced with these could ... drop a 40mm grenade into a window about
this big at 300 or 400 yards. Really an excellent small arm.
The problem was it was single shot, there wasn't a very good short range system.
Like if you got surprised at close range there wasn't a whole lot you could do.
You don't want that grenade going off right in your face,
and it would take 30 yards before it could arm.
There was experimentation with a huge variety of other munitions.
They had a buckshot round, they tried a flechette round.
They had a .22 calibre, it's like a hornet's nest of I think 18
.22 rimfire cartridges all in a single 40mm shell.
None of those things were really all that effective.
People think about a 40mm buckshot round
and think it had to be just absolutely devastatingly effective,
but it's important to remember that you are limited to a relatively mild recoil impulse.
That makes this whole weapon possible.
You are not going to be able to take a 12 gauge buckshot load and scale it up
and have like 1,200 feet per second on 6 ounces of buckshot or something,
whatever you could cram into a 40mm round. It was relatively low velocity.
And while it sounds cool on paper, it just didn't really stand up in practice.
And so what you ended up with was guys who were carrying an M79
and then they would have something like a 1911 as a backup sidearm for personal defence.
What they wanted, what people realised would be a lot better, is
"Well, it's a single shot launcher anyway. What if we find a way to like stick this onto a rifle?"
And that led to the development of underbarrel grenade launchers.
There are a lot of tie-ins here to Project SPIW, which is tangentially related.
Which was in fact a large driving force in development of the 40mm grenade system.
Those are subjects for other videos.
But with the development and the adoption of the M79
they immediately started looking for underbarrel versions.
That would become the XM-148, which we have a video on, which had its own problems,
and then that became the M203 which is still used today, or was until very recently.
The M203 went into production about 1970, that's about when the M79 left production, 1971.
But it wasn't replaced in all roles immediately,
and these things were in use certainly as late as Desert Storm.
And they'll still be found all over the world because they are
simple, reliable, and very effective weapon systems.
I hope you guys enjoyed this look at the M79.
You should definitely stick around, because the next video in this little series
is going to be on the pump action version of it, so stay tuned for that.
Thanks for watching.