Carl Gustav 84 - Why so heavy?

#1
I don't think anyone's asked this. I know they made an aluminium 18lb model, but looking at the 34lb steel version;

I used to think that the gas out the back formed a high-pressure area which created a kind of virtual breech wall so that some of the later gas couldn't escape so easily, so allowing the chamber pressures to climb and the projectile to move. That can't be right, though, because then (I think) there would have been recoil.

So, presumably, what actually happens is that a bucketload of hot gas flies out the back and you get a simple (Newtonian) explosion - mass times velocity of the gas equals mass times velocity of the projectile, the weapon stays still.

Now if that's true why was it so bloody heavy? Presumably you would need a load of steel around the round itself to resist the pressure caused by the rapid expansion of gas, but the breech pressure once the projectile starts to move would (presumably) be half of fanny adams. A rifle needs a strong barrel because there is burning propellant causing high pressures progressively accelerating the bullet the whole way up the barrell. But if all you are doing is (essentially) causing an explosion and then directing one bit of it (the projectile) I can't see that you need a uniform thickness on the barrell. Most of the barrell is just there to hold the rifling, no?

Similarly if the venturi just protects your legs when prone you could half it, make it of something else lighter, or adopt a different prone firing position.

The reason I ask is that you might think that the total propellant to drive a mass a distance must be similar whether you use fast burning stuff in a recoilless rifle or slow burning stuff in a rocket. If we could have a thin (and light) barrell maybe we could have something cheap, effective and accurate for Afghanistan.
 
#2
Robustness, the term squaddie proof springs to mind. :wink:

Charlie G was one of my old favourites. I used to prefer No 2ing/loading rather than firing and always closed and locked the hinged breech with a flourish whilst proceeding to check the back blast area. :wink:

The Carl Gustav used a rifled barrel for spin-stabilizing its rounds
The use of the recoilless firing system allowed the Carl Gustav to use ammunition containing considerably more propellant, firing its rounds at 290 m/s, as opposed to about 105 m/s
The result was superior accuracy at longer ranges.
http://en.wikipedia.org/wiki/Carl_Gustav_recoilless_rifle
 
#4
The reason that its so heavy is because the explosion travels in every direction, not just front and back.

Look into Newtons' Laws of Motion; for every action there is an equal and opposite reaction. The huge gas plume will act as the "reaction" for the force driving the round forward.

Have I just been wah'd?
 
#5
gobbyidiot said:
but the breech pressure once the projectile starts to move would (presumably) be half of fanny adams.
Nope. It doesn't instantly achieve that speed, it has to accelerate; the pressure is sufficient to keep accelerating the projectile most of the time that it's in the barrel, and certainly hasn't dropped to zero by the time the shell leaves. Watch for the muzzle gases in this clip:

http://www.youtube.com/watch?v=VvRzOO_avCc&feature=related

Think about "what's the pressure immediately behind the shell"; it's high (to get the shell moving) and it it is being applied equally to the back of the round, outwards against the barrel, and backwards against all of the air that's between it and the venturi and freeeeeddddoooommmmm.....

You could argue that the barrel doesn't need to be as strong at the front as it does towards the back, but that would make it expensive. Remember, this is a 1960s design aimed at conscript armies - cheap and cheerful is the name of the game, and a straight steel tube fits the bill. The weight reduction in the barrel is possible through the use of carbon fibre (the alloys got used on the other non-pressure-loaded bits, e.g. bipod), and affordable through the shrinking of armies.

gobbyidiot said:
The reason I ask is that you might think that the total propellant to drive a mass a distance must be similar whether you use fast burning stuff in a recoilless rifle or slow burning stuff in a rocket. If we could have a thin (and light) barrell maybe we could have something cheap, effective and accurate for Afghanistan.
Already exists. Buy a bucketload of M72 or RPG-7.
 
#6
Gravelbelly said:
gobbyidiot said:
but the breech pressure once the projectile starts to move would (presumably) be half of fanny adams.
Nope. It doesn't instantly achieve that speed, it has to accelerate; the pressure is sufficient to keep accelerating the projectile most of the time that it's in the barrel, and certainly hasn't dropped to zero by the time the shell leaves. Watch for the muzzle gases in this clip
Yup, it has to accelerate because if it is at rest and goes quickly it's undergone an acceleration, I just can't convince myself that the way to think about it is "High chamber pressures throughout, like any other rifle", rather than "Shitload of gas heading one way requiring equal and opposite other way".

Mind you, it took me two attempts to get a "B" on my Higher Physics :D
 
#8
polar69 said:
I just remember them being f**ing heavy, although why a crab needed to fire a charlie g is another story
And loud, don't forget f**ing loud.
 
#10
I think it had more to do with date and technology . The newer M3 version is half weight of the M2. An advance in metallurgy means you can make it of lighter metal. You may also have had a bigger fudge factor in the original M2s.

I notice that in the septic videos the No2 does a runner the wimp.
 
#11
Steven said:
polar69 said:
I just remember them being f**ing heavy, although why a crab needed to fire a charlie g is another story
And loud, don't forget f**ing loud.
My ears have been ringing since 1976.....those little pink ear plugs were no effin' use and the Amplivox weren't much better.

:(

Rodney2q
 
#12
Rodney2q said:
My ears have been ringing since 1976.....those little pink ear plugs were no effin' use and the Amplivox weren't much better.

:(

Rodney2q
I fired it once with double ear protection and it didn't seem too bad - either that or it was so feckin loud it went beyond loud. Onlookers thought it was louder than I did.

Get this - I know a bloke whose foam plugs contracted and dropped out in the cold in Norway during a live attack - he fired 8 rounds with no protection. Totally ridiculous. My ears hurt thinking about it. Easy to be wise after the event but I'd have had the number two put his fingers in my ears.
 
#13
Don't forget the beasting factor, if it wasn't so heavy it wouldn't be the same shouting at the lads.
Strong tradition going back to Roman times and Marius' Mules.
 
#14
They showed the 'Latest' offering in the Charlie G line on Future Weapons Discovery Channel the other week.
It can be fired from inside a Building or a Wagon/AFV.
john
Equal and opposite reaction.
Big heavy lump, slowly out the front equals very light glasses and whatever ultra fast, out the back end.
 
#15
I was a Charlie G'r in 24 Fld Sqn for about six months.....wasnt too bad. Then I went the to LMG and I found that harder going especially tabbing and alternating with my No2 with that big cumbersome box of mags. Sometimes though we used to distribute. But I was a wary bastard and loved every minute of them both!
 
#17
Rodney2q said:
Steven said:
polar69 said:
I just remember them being f**ing heavy, although why a crab needed to fire a charlie g is another story
And loud, don't forget f**ing loud.
My ears have been ringing since 1976.....those little pink ear plugs were no effin' use and the Amplivox weren't much better.

:(

Rodney2q
The best description I heard of firing the Charlie G was: "It is like the world farting and the cheeks of its arse slapping you around the head"
 
#18
Fell down a field ditch one night in Germany when carrying the Charlie G.. didn't hurt really..... until I woke up!
Fekin thing was un-balanced when carrying it with that sling that was big enough to carry 4tonner and caught on anything and everything, and debussin from the the armoured personnel tonner!!!!!!!!
feck me like geriatrics gettin off a bus!!!!!!
never got to fire it circa 1982 one round.......yes thats ONE round issued for the whole Batt on an FTX per year! and you lot think you got problems with kit shortages today HA!!!
You got it cushty mate!!!!!!!
Seriously though it was a piece of shit!!! heavy and would have been un-useable in reality, better to carry more gimpy ammo than 64mm rounds.
 
#19
gobbyidiot said:
Gravelbelly said:
gobbyidiot said:
but the breech pressure once the projectile starts to move would (presumably) be half of fanny adams.
Nope. It doesn't instantly achieve that speed, it has to accelerate; the pressure is sufficient to keep accelerating the projectile most of the time that it's in the barrel, and certainly hasn't dropped to zero by the time the shell leaves. Watch for the muzzle gases in this clip
Yup, it has to accelerate because if it is at rest and goes quickly it's undergone an acceleration, I just can't convince myself that the way to think about it is "High chamber pressures throughout, like any other rifle", rather than "Shitload of gas heading one way requiring equal and opposite other way".
The difference is that a normal firearm has equal pressures (ish) over the entire barrel, bolt face, and back of the bullet until the bullet leaves the weapon.

If you had a set of magic pressure gauges to use on your 84mm MAW (showing my age - thank f**k we don't have SMG any more), and you measured the pressure just behind the shell; a bit further back; a bit further yet; and so on until you got to the venturi; you'd see gradually lower pressure readings. You have a peak pressure slightly behind the shell, and a rapid fall-off, unlike the rifle with its much more even pressure. That peak pressure will travel forwards up the barrel just behind the shell, with its value dropping as it goes.
 
#20
My favourite part of shooting the '84' was once when I was checking the back-blast area and I saw my CSM, Coy OC, the RSM and the CO had all poked their heads up and were way too close so I couldn't fire. I shouted once for them to clear and when they didn't I screamed it at the top of my voice adding invective and they all hit the deck pretty smartish. It made me smile but by fcuk that thing was heavy on a long tab and also gave the lie to the idea of ear defenders on the range. Health and safety? Fcuk off! So when you then tell them you are proper deaf in one ear they say ' did you wear ear defenders?'. Ooh it makes I fume so it does.
 

Similar threads

Latest Threads

Top