M1 Abrams Tank

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I was watching the Science channel.
It was about the building and theory of the design for the M1 Abrams Tank.
My question is what is the purpose of the bulge in the middle of the 120 mm canon?
I seen some are shorter that others.
 

indyartisan

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The bore evacuator reduces the risk of propellant gases entering the crew compartment, allowing a greater rate of fire. It causesa pressure differential in the barrel, ensuring gases leave from the muzzle end of the barrel/tube.
 

BigMoose

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The M256 120MM smoothbore (yep, no rifling) lump is indeed a bore evacuator.

https://www.inetres.com/gp/military/cv/weapon/M256.html



its really a German Rheinmetall 120mm L44 smoothbore gun
 
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The bore evacuator reduces the risk of propellant gases entering the crew compartment, allowing a greater rate of fire. It causesa pressure differential in the barrel, ensuring gases leave from the muzzle end of the barrel/tube.


Thanks guys, Now I really wonder how this person came up with the idea and design.
There are some great minds working out there.
 

blue2golf

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Less bore wear and tank rounds can be fin stabilized and work better with smooth bore.

True but like Dalton said, "Opinions vary."

Brits hold the longest recorded tank on tank kill, using a Royal Ordinance rifled 120mm main gun at 2.9 miles during Desert Storm.
 

Tombs

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Ok, next question, why a smoothbore in a precision weapon?

Because the only reason to use rifling in a modern tank is for firing hesh, where you need projectile rotation to make the warhead behave properly.

HEAT rounds perform DRAMATICALLY better from a smooth bore. Considering HEAT and APFSDS are the 2 primary rounds used today, both of which would perform worse from a rifled bore, the rifled tank cannon is now an antiquated concept. Might still make sense for an assault gun, firing HESH, but that seems to have gone extinct as well.

True but like Dalton said, "Opinions vary."
Brits hold the longest recorded tank on tank kill, using a Royal Ordinance rifled 120mm main gun at 2.9 miles during Desert Storm.

The Abrams is just as capable of making a shot like that, if not moreso. Battlefield entropy allows the stars to align from time to time.
 

Hawkeye

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I was watching the Science channel.
It was about the building and theory of the design for the M1 Abrams Tank.
My question is what is the purpose of the bulge in the middle of the 120 mm canon?
I seen some are shorter that others.

the bore evacuator is not new with the Abrams. The M-41, M-47, M-48 and M-60 series all had bore evacuators on their cannons. The 76 and 90 mm guns had them closer to the muzzle. the 105 mm (a British design) had them more mid-barrel.
 
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The bore evacuator reduces the risk of propellant gases entering the crew compartment, allowing a greater rate of fire. It causesa pressure differential in the barrel, ensuring gases leave from the muzzle end of the barrel/tube.

Yep. And if you've never been inside a tank during a gunnery, the fumes from the main gun are rather unpleasant. It'll burn your eyes and mouth/throat almost like tear gas.

The evacuator isn't just a wide part of the bore, it's actually a casing over the outside of the barrel and there's holes drilled through the barrel that allow just enough gases out of the bore to create the pressure differential. Even with the evacuator a lot of fumes still enter the turret and there is a ventilator that creates positive pressure inside the turret to push the fumes out.

/former tanker
//death before dismount
 

daddyusmaximus

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the bore evacuator is not new with the Abrams. The M-41, M-47, M-48 and M-60 series all had bore evacuators on their cannons. The 76 and 90 mm guns had them closer to the muzzle. the 105 mm (a British design) had them more mid-barrel.

Yup. We had them on our M60A3, and on the first M1 tanks that had the same M68 105mm gun. (a copy of the Royal Ordnance L7 gun)

My M60A3 at Graf in 1982... about 2/3 down the barrel, right over the leading edge of the front left fender.

 

HoughMade

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True but like Dalton said, "Opinions vary."

Brits hold the longest recorded tank on tank kill, using a Royal Ordinance rifled 120mm main gun at 2.9 miles during Desert Storm.

Opinions do not vary as to why they chose smoothbore...which was the question.
 

blue2golf

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Yep. And if you've never been inside a tank during a gunnery, the fumes from the main gun are rather unpleasant. It'll burn your eyes and mouth/throat almost like tear gas.

The evacuator isn't just a wide part of the bore, it's actually a casing over the outside of the barrel and there's holes drilled through the barrel that allow just enough gases out of the bore to create the pressure differential. Even with the evacuator a lot of fumes still enter the turret and there is a ventilator that creates positive pressure inside the turret to push the fumes out.

/former tanker
//death before dismount

Yes they can be unpleasant, but I'd like to breathe them in again. Something you don't forget.
 

daddyusmaximus

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The question was about a precision weapon and the method chosen to achieve accuracy. There is still a place for rifled main guns on tanks.

Not in the 80's through post 9/11. They didn't use tanks anymore for infantry support like they used to in the past. For a long time tanks were limited to tank on tank warfare. (thanks to the Soviet threat) Once they developed the fin stabilized rounds, they went away from the rifled main guns. It stayed that way til long after the collapse of the Soviet Union.

If they ever come back to a rifled main gun, it will be because of the asymmetrical warfare we're embroiled in nowadays with insurgents as the main enemy, and troops once again using armor in the support role. We may once again see tanks using HE and other type rounds. I'd love to see the beehive brought back. I don't see that happening, however, as we still have other platforms to offer supporting fires, and Russia, China, and other nations have armor we may need to deal with.

I think we need a new light tank like a modern Sheridan, fast with band tracks, possibly a hybrid drive, amphibious, and a 30mm main gun. It could fire HE rounds to support troops, or the same DU rounds as the A-10 at armored vehicles.
 
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