"It's not a tumah"
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
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.
Less bore wear and tank rounds can be fin stabilized and work better with smooth bore.
Ok, next question, why a smoothbore in a precision weapon?
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.
Less bore wear and tank rounds can be fin stabilized and work better with smooth bore.
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 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.
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.
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.
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
Opinions do not vary as to why they chose smoothbore...which was the question.
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.