Muzzle brakes on AT guns?

[Makes The Jelly Judder]

Right, my understanding is that the muzzle brake on tank guns is there to reduce the recoil of the gun.

Now I can understand this on guns in tanks due to the cramped conditions in the turret. What I don't understand is why the muzzle brakes exist on towed AA and AT guns, surely the recoil of the guns doesn't really matter for these? Guns I can think off that have muzzle brakes are:

AT Guns

German 75mm

German 88mm

German 128mm

Russian 100mm

AA Guns

Russian 85mm

Russian 75mm

Plus there are various Arty guns that have these things attached too.

Surely the muzzle break ruduces velocity and accuracy of the guns? So what gives? Are these simply tank guns placed in a gun carrage for ease of production(AA guns and arty excepted)?

[Guest Mike]

Carriages can only take so much recoil force - muzzle brakes are a common way to try to keep the overall gun size down by reducing the recoil force hence allowing a smaller carrieage.

Sometimes muzzle brakes were added after experience had shown that the recoil forces weer too high and resulted in carriages being damaged or whatever. Sometimes they were designed in from the start.

Apaprently there is or can be a small decrease in muzzle velocity from having a good brake fitted, but it's only single-digit metres per second, so not too much of a problem.

[Bastables]

Ah ha, but the gun has to deal with less recoil and that means it can be lighter than a comparable gun sans muzzle brake.

[Redwolf]

Well, for a very high velocity gun like an AT gun it should be more substancial slowdown. I think the last thread on the issue had some numbers.

The whole thing is a tradeoff of more than two parameters. While the speed at the muzzle is reduced for the same charge, you an use a bigger charge, get the same projectile speed and the same recoil, but at the expense of higher stress on the chamber.

So if you have a gun where the chamber has reserves but the carriage is overloaded you can play with muzzle brakes, charge size and barrel length to arrive at a better average utilization of all your parts (i.e. better gun performance and/or reduced load on the formerly overloaded part for longer life of the gun).

[Guest Mike]

The bit about the reduction in velocity ceoms from teh thread on the T34/SU-76 armament difference, where, IIRC, the mv difference is less than 10m/s between the braked Su-76 and the unbraked T34.

Of course eth guns are different too, but use the same ammo and are pretty much the same calibre.

[Redwolf]

Ah, yes.

BFC give the SU-76m gun 655 m/sec and the T-34 gun 680 m/sec.

That's roughly 4% speed and 8% kinetic energy and this is not even an especially high-performance gun.

[ June 23, 2003, 10:44 PM: Message edited by: redwolf ]

[Stalin's Organ]

I stand corrected - I guess it's a bit more than I remembered then!

Another comparison - the Germans used the barrels from French 75's to make improvised AT guns - they used captured French & Polish ammo, had a muzzle-brake fitted & lost 5m/s viz the original (575 - 570m/s).

They were fitted to PAK 38 chassis (the 50mmL60), and a few to early Pak40 chassis.

[ June 24, 2003, 12:48 AM: Message edited by: Stalin's Organ ]

[MikeyD]

Here's an article on muzzle brakes written by the indomitable R.P. Hunnicutt:

http://www.activevr.com/afv/muzzle.html

If you've ever seen WWII footage of a 6pdr anti-tank gun bouncing-while-firing while placed on a cobblestone street (where its trailing legs can't get a good grip) it's enough to make you wonder how the gunner dares man his weapon! It looks like much more recoil and the gun carraige would flip over!

The Flak 88 didn't need a muzzle brake because of the stability of its cruciform legs staked into the ground. The Russian 76mm field gun (Zis-2 or 3, I keep forgetting) uses the game field carriage as the 57mm gun and so needs a muzzle brake to bring the recoil down to levels the carriage can tolerate.

[ June 24, 2003, 10:22 AM: Message edited by: MikeyD ]

[John D Salt]

Originally posted by redwolf:

Well, for a very high velocity gun like an AT gun it should be more substancial slowdown.

[snips]

Why should a muzzle brake produce any loss of m.v.?

Assuming that the driving band produces proper obturation, the propellant gases do not act on the brake until the projectile clears the muzzle, as is mentioned in the Hunnicutt article referred to above.

All the best,

John.

[Bone_Vulture]

I was thinking the same thing as John. But doesn't the muzzle have to be rather airtight (projectile still to exit the barrel) in order to veer some of the combustion gases to the brake vents? If so, the round will suffer from a momentary friction after the pressure peak of ignition inside the barrel.

[Redwolf]

The air that was in the barrel before the shot is subject to the same brake mechanism as the air and explosion gases escaping after the shot.

The air in front of the projectile doesn't move out of the way freely with a brake, a part of it bounces off the muzzle brake and is then "in the way" of the projectile.

Or in other words, the projectile has a harder time moving through the air that it is pushing out of th barrel, because a part of that air is now being compressed against the brake, establishing much greater resistence for the projectile.

[Doodlebug]

Can't muzzle brakes also cause problems with APDS rounds in that they could be damaged by the sabots as the flew off?

[MikeyD]

To fire APDS with a muzzle brake you have to be very careful in the design in order to avoid problems, but it has been done.

APDS damage to the muzzle brake is something neither the Russians or the Germans had to worry about, since they didn't field APDS. But the Brits did and their towed 6 pounders had muzzle brakes (as the modern 6pdr-derived 90mm Mecar low recoil gun has a muzzle brake and now fires APFSDS).

I don't quite follow the "muzzle brake needs to be airtight" theory, especially considering the ISU-152's highly effective multi-slotted muzzle brake looks as open as a set of venitian blinds! As to the round finding significantly greater air resistance with a muzzle brake, all rounds would be pushing a column of air out of the tube from the moment of firing, any resistance not counterbalanced by the explosion behind it would only occur in the last 8 inches(?) of travel through the brak itself as perhaps 30% of the gasses behind it are redirected.

[Redwolf]

Originally posted by MikeyD:

I don't quite follow the "muzzle brake needs to be airtight" theory,

? Who said something like that.

As to the round finding significantly greater air resistance with a muzzle brake, all rounds would be pushing a column of air out of the tube from the moment of firing, any resistance not counterbalanced by the explosion behind it would only occur in the last 8 inches(?) of travel through the brak itself as perhaps 30% of the gasses behind it are redirected.

Exactly. That is why you only have a slowdown of less than 10%. But some slowdown in unavoidable with any working muzzle brake.

[rexford]

Originally posted by John D Salt:

</font><blockquote>quote:</font><hr />Originally posted by redwolf:

Well, for a very high velocity gun like an AT gun it should be more substancial slowdown.

[snips]

Why should a muzzle brake produce any loss of m.v.?

Assuming that the driving band produces proper obturation, the propellant gases do not act on the brake until the projectile clears the muzzle, as is mentioned in the Hunnicutt article referred to above.

All the best,

John. </font>

[Monty]

I have read that muzzlebreaks give a smaller dustcloud so the tanks of guns are harder to spot for the enemy.

Is this right ? ?

Monty

[Redwolf]

No, it's the opposite.

Since more air is moving away from the gun's muzzle at high angles, more dust is being kicked up. I read descriptions of muzzle brakes being removed in dusty areas improve the gunner's life expectation.

You could try to get fancy and build a muzzle brake that diverts less air to the bottom and more to sides and upwards, but I don't know whther that has been tried and I guess the asymmetrical forces on the barrel are not welcome either, at least for indirect firing artillery.

[Makes The Jelly Judder]

Thanks for all the replys guys, all makes perfect sense, just a question of balancing all the factors for the best effect.

Right, Ive got another question. When an AT gun was found to be underperforming i.e 2pdr its replaced by a gun with a larger diameter shell i.e. the 6pdr. The names of these guns suggests that its not really the size of the shell that is important but its mass. I assume that penetration is directly related to momentum i.e. velocity * mass. My question then is why didnt the 2pdr just get a heaver (i.e longer) shell, wouldn't that work just as well? What about HE, why increase the diameter of the shell when you can just make the shell longer and stuff more explosives into it?

[ June 28, 2003, 09:57 PM: Message edited by: Makes The Jelly Judder ]

[Stalin's Organ]

For starters guns are chambered for a particular size of cartridge - so if you just slap a heavier shell on the front it goes slower.

If you do rechamber the gun you have higher pressures - a larger propellant chargge pushing a heavier projectile, so you also have to increase the weight of hte breech and barrel to contain those pressures - I imagine it would soon become an exercise in futility as your 500 ton "2 pounder" struggles to contain hte pressures incured by firing a 17 lb shot

IIRC Kinetic energy = 1/2 * mass * velocity*velocity (v^2) - so in a simplistic sense it's better to go faster than to becoem heavier.

[Makes The Jelly Judder]

Ok, I kinda figured that the velocity of the shellwould be seriously impacted, but low velocity for the HE shells wouldn't be too much of problem.

Could gun crews be given a couple of huge short range HE shells for use in situations where they might be overrun.

[Mr. Tittles]

What about the 75mmL/70 'Panther' gun? It was used with a brake (in the tank) and without the brake in the Jgpnz IV L70.

Was it used in the TD without a brake because it was low to the ground? Kicking up too much dust? Not needed because the interior had sufficient recoil room?

Most modern tanks do not sport these. They do have bore evacuators. The main purpose of them is to collect and discharge particulate from the propellent. But could they also have some sort of brake effect?

[Redwolf]

Originally posted by Mr. Tittles:

What about the 75mmL/70 'Panther' gun? It was used with a brake (in the tank) and without the brake in the Jgpnz IV L70.

Was it used in the TD without a brake because it was low to the ground? Kicking up too much dust? Not needed because the interior had sufficient recoil room?

That vehicle had the brake removed because it was too prone to get its gun stuck into the earth when moving over uneven terrain, especially when crossing trenches.

I also assume that the gun mount could sustain more recoil than the turret mechanism in the Panther. Respectivly for the Jagdpanzer the wear didn't matter much but wearing out the turret ring is a bad thing.

[Bastables]

Originally posted by redwolf:

</font><blockquote>quote:</font><hr />Originally posted by Mr. Tittles:

What about the 75mmL/70 'Panther' gun? It was used with a brake (in the tank) and without the brake in the Jgpnz IV L70.

Was it used in the TD without a brake because it was low to the ground? Kicking up too much dust? Not needed because the interior had sufficient recoil room?

That vehicle had the brake removed because it was too prone to get its gun stuck into the earth when moving over uneven terrain, especially when crossing trenches.

I also assume that the gun mount could sustain more recoil than the turret mechanism in the Panther. Respectivly for the Jagdpanzer the wear didn't matter much but wearing out the turret ring is a bad thing. </font>

[Michael Emrys]

Originally posted by Makes The Jelly Judder:

When an AT gun was found to be underperforming i.e 2pdr its replaced by a gun with a larger diameter shell i.e. the 6pdr. The names of these guns suggests that its not really the size of the shell that is important but its mass. I assume that penetration is directly related to momentum i.e. velocity * mass. My question then is why didnt the 2pdr just get a heaver (i.e longer) shell, wouldn't that work just as well?

To elaborate just a bit on what Stalin's Organ has already posted, no, for the following reason. A larger diameter shell (or shot, as in this case) has a larger base area. That means that for a given chamber pressure, more motive force will be applied to accelerate it up the tube. More mass is definitely nice to have, but you have to move that mass to a useful velocity.

Now, a larger diameter also means greater frontal area, ie. more aerodynamic drag once the the shot/shell leaves the tube, so there are tradeoffs here. One way around them is to use—ta-da!—discarding sabot, which gives a large base area but without the frontal area after the round is on its way. Squeeze bore is another approach to the same problem.

What about HE, why increase the diameter of the shell when you can just make the shell longer and stuff more explosives into it?

Sometimes in fact that was done. If you compare some of the HE rounds to the AP rounds for the same gun, you may note that the HE rounds are noticeably longer. That doesn't necessarily mean that they are heavier though, since the HE filler is less dense than the metal it replaces.

Michael

[ June 30, 2003, 02:39 AM: Message edited by: Michael emrys ]

[JonS]

Originally posted by redwolf:

No, it's the opposite.

Since more air is moving away from the gun's muzzle at high angles, more dust is being kicked up. I read descriptions of muzzle brakes being removed in dusty areas improve the gunner's life expectation.

You could try to get fancy and build a muzzle brake that diverts less air to the bottom and more to sides and upwards, but I don't know whther that has been tried and I guess the asymmetrical forces on the barrel are not welcome either, at least for indirect firing artillery.

Er, I don't know where you get that from. Pretty much every MB I've seen has the 'holes' to the sides. Coincidence? I doubt it.

This is a short speil on muzzle brakes.