aws@vax3.iti.org (Allen W. Sherzer) (04/29/89)
From: aws@vax3.iti.org (Allen W. Sherzer) My dad has a question: Why do modern tanks use a smooth bore barrel on their guns? Doesn't that hurt accuracy? Thanks Allen ---------------------------------------------------------------------------- | Allen Sherzer | DON'T BUILD MORE NUKES | | aws@iti.org | until we use the ones we have. | ----------------------------------------------------------------------------
henry@zoo.toronto.edu (Henry Spencer) (05/02/89)
From: henry@zoo.toronto.edu (Henry Spencer) >My dad has a question: Why do modern tanks use a smooth bore barrel >on their guns? Doesn't that hurt accuracy? The shells are generally fin-stabilized, which gets back a lot of the accuracy. Not all, last I heard, but a lot. Smoothbore guns have a higher muzzle velocity, due to reduced barrel drag, and are better suited to laser-guided shells and shaped-charge shells, which don't want to spin. (For laser guidance, spin complicates guidance; for shaped charges, centrifugal force interferes with formation of the "jet" when the charge fires.) I'd imagine the barrels also last longer. Of late, it's looked worthwhile. Henry Spencer at U of Toronto Zoology uunet!attcan!utzoo!henry henry@zoo.toronto.edu
malloy@nprdc.navy.mil (Sean Malloy) (05/02/89)
From: malloy@nprdc.navy.mil (Sean Malloy) In article <6077@cbnews.ATT.COM> aws@vax3.iti.org (Allen W. Sherzer) writes: >My dad has a question: Why do modern tanks use a smooth bore barrel >on their guns? Doesn't that hurt accuracy? The purpose of rifling a barrel is to spin the projectile so that it is more resistant to wobbling in flight, which generates unbalanced aerodynamic forces that reduce the accuracy of the gun. Most of the shells that are used by front-line tanks come in two types: APFSDS (Armor Piercing Fin Stabilized Discarding Sabot) and HEAT (High Explosive Anti Tank). An APFSDS round is essentially a large metal dart -- a (relatively) thin pointed rod with fins on the back that stabilize the round the same way an arrow is stabilized, so that the shell doesn't have to be spun for stabilization. The rifling of the barrel places additional drag on the shell (in order to transform some of the driving force from accelerating the shell to spinning the shell), and also wears down the rifling. Without rifling, the shells can be fired at higher muzzle velocities, and reduce the barrel wear. For HEAT rounds, the answer is a lot simpler. HEAT rounds, also called 'shaped-charge warheads', depend on the geometry of the warhead to generate a high-speed jet of molten metal from a metal facing on a conical depression in an explosive charge, which penetrates the target's armor. If you spin a HEAT round, the rotation tends to force the metal facing of the explosive away from the centerline of the round when it detonates, so the warhead can't form the jet properly -- the penetration goes _way_ down. Sean Malloy | "The proton absorbs a photon Navy Personnel Research & Development Center | and emits two morons, a San Diego, CA 92152-6800 | lepton, a boson, and a malloy@nprdc.navy.mil | boson's mate. Why did I ever | take high-energy physics?"
maniac%garnet.Berkeley.EDU@ucbvax.Berkeley.EDU (George W. Herbert) (05/03/89)
From: maniac%garnet.Berkeley.EDU@ucbvax.Berkeley.EDU (George W. Herbert) In article <6155@cbnews.ATT.COM> henry@zoo.toronto.edu (Henry Spencer) writes: >>My dad has a question: Why do modern tanks use a smooth bore barrel >>on their guns? Doesn't that hurt accuracy? >The shells are generally fin-stabilized, which gets back a lot of the >accuracy. Not all, last I heard, but a lot. Smoothbore guns have a Last I heard, anything from 20mm up was much MORE accurate in DSFS than solid, rotating shot. Especially since the wind and ballistic coeficients go through the roof with such rounds. DSFS: Discarding Sabot Fin Stabilized. Generally seen as 'APFSDS' or variant, this refers to the mechanism of mounting a very small diameter rod with fins on the back inside a carrier shell of aluminum or similar light material, which falls away after the round leaves the barrel of the gun. This gives a larger barrel, with lower pressure (or higher energy) than the straight rod size, and fin-stabilization for accuracy. The rod is often a Tungsten or Uranium (depleted, NOT radioactive) cored steel rod, those materials giving much higher shot density and energy.