smoothbore vs rifled main guns

[Sublime]

im curious. using the m1 as an example it originally used a 105mm rifled L7 cannon, later adopting a 120mm rheinmetall 120mm. why? aremt rifled guns more accurate? in the case of russian armor that fires missiles from the main gun sometimes too i can understand but for shell only guns this confuses me..?

[c3k]

Lots of reasons. One, simple, reason is for higher muzzle velocity. Rifling is a drag. Newer finned sabots are as accurate (or moreso) than rifled rounds. This gives smoothbore the edge.

 

Again, that's a fairly simplistic explanation.

[Panzerpanic]

Also , in the soviet/russian case , its easier to shoot gun lunched atgm from smooyhbore. Still they get around as the t-55 am can shoot bastion but i dont know if its rifle or not. Also  for the brit, isn it the charm 3 a sabot?

[MikeyD]

I recall reading an article waaaaay back in the early 80s(?) about them having fits getting the Rheinmetall gun as accurate as the rifled 105. Even the non-spinning 105mm APFSDS dart round was getting better accuracy. That's because the 105 round's slip rings weren't 100% efficient and imparted a slight spin. A flat-flying round deviating from target would keep pulling off-line in the same direction. A slightly spinning round would deviate in an increasingly large circle around the rotation axis. That's about the time we saw wind sensors appearing on tanks. Measuring the cross wind in an effort to correct for drift. That, of course, was approx. 35 years ago.

Edited May 20, 2015 by MikeyD

[DreDay]

Also , in the soviet/russian case , its easier to shoot gun lunched atgm from smooyhbore. Still they get around as the t-55 am can shoot bastion but i dont know if its rifle or not. Also  for the brit, isn it the charm 3 a sabot?

 

I am not so sure about this claim. ATGMs have their own propellant boosters, so I don't see why the gun tube type would matter so much... I mean, what about BMP-3/BMD-4 that have low velocity guns that still fire advanced ATGMS?

[Panzerpanic]

well i thought that the rifling in the ghe gun would made the missil,e spin (wich is not a good thing) and with the smoothbore...well no spinning.

[c3k]

Slip-rings were used by the British to enable the L7 gun to fire HESH rounds effectively. That kept the round from spinning.

 

Rheinmetall got caught cheating in the M1 gun shoot-off. They used APFSDS projectiles with weighted noses to improve their accuracy, not the standard rounds.

 

The British weapons development took rifled tank guns as far as technology allowed. The German approach showed that (with modern tech), smoothbore had finally surpassed rifled weapons for developing kinetic energy penetrators.

[Melchior]

Imparting a centrifugal force onto the penetrator decreases the energy it directs straight into the impact point. Fin stabilizing essentially makes rifling needless for accuracy.

Older HEAT rounds also didn't do very well fired from a rifled gun. The spinning would disperse the warhead's effect instead of focusing it. Though that isn't really a problem today because AFAIK modern HEAT rounds sometimes mount the warhead on bearings. Like what C3K says above.

[Los]

Yes, your basic APDSFS armor piercing discarding sabot FIN STABILIZED....

Edited May 22, 2015 by Los

[Apocal]

im curious. using the m1 as an example it originally used a 105mm rifled L7 cannon, later adopting a 120mm rheinmetall 120mm. why? aremt rifled guns more accurate?

 

The 105 anti-tank rounds had inferior penetration and the Soviets had better armor. Doesn't matter if you can put the round on target further away if it won't do anything to the tank's armor when it gets there...

[MikeyD]

Brits still uses a rifled gun. Wasn't it a Challenger that got credited with a max range hit awhile ago? Of course the APFSDS rounds have slip rings to minimize rotation.

 

If (very) distant memory serves, a finned projectile tends to pull into a cross-wind rather like the rudder on a boat changing its direction. The big advantage of smooth more guns is all of the muzzle energy goes into velocity. I recall the Tiger I rifled gun had progressive pitch rifling, The further down the gun tube the tighter the rifling got. That was meant to reduce initial torque, get a bit extra of the muzzle energy into pushing the projectile forward.

Edited May 22, 2015 by MikeyD

[Melchior]

The British utilize rifling still because they prefer to use HESH rounds almost as much AP rounds and rifling increases the "pancake" area of the round. HESH is known for being great against buildings and can either be very useful or very useless against armored vehicles. The round needs to impact and flatten itself against a surface which is problematic if the surface is rounded like a T-64 turret or has lots of stuff on it like tracks, shovels, spaced armor, etc. The British don't seem to have had many problems with that sort of thing though.

[c3k]

Progressive rifling is an efficiency thing. With constant pitch rifling, the projectile loses a bit of oomph with the initial bit. (The projectile is thrust, with no spin, into a "fully" spun twist.) As the velocity increases down the bore, the spin rate increases, yet the pitch is constant. Progressive rifling smoothly accelerates the spin in concert with the increase in velocity. Pitch of the rifling is tied to velocity of the projectile.

 

It is hard to manufacture.

It is hard to calculate the correct progressive rifling rate AND ensure that all the projectiles meet that profile.

The benefits are not very noticeable.

 

(Crosswind effects on APFSDS is countered by the use of wind sensors/lasers/etc. The spin of rifled rounds produces minor other rotational effects of their own, in addition to those of wind.)

[panzersaurkrautwerfer]

Another thing with mentioning is that smoothbores have significantly better barrel life on top of the round performance stuff mentioned earlier.  Additionally the accuracy problems of a near to past end of life smoothbore tube are less pronounced than when rifling goes bad. 

 

 

 

Wasn't it a Challenger that got credited with a max range hit awhile ag

 

It was, but the reality of the shot was that someone in a Leo 2/M1/Mervaka could have made it too.  It wasn't a special rifled barrel thing, it was the opportunity of a totally exposed enemy tank that was stationary, plus a crew that was skilled enough to work around some of the stuff that's less optimal at range (the laser especially, the farther it goes, the less "certain" it can be).

[JonS]

It is hard to manufacture.

The benefits are not very noticeable.

aren't those things true of all recent improvements in accuracy and hitting power? APFSDS, for example, is insanely difficult and complex to manufacture.