PDA

View Full Version : What makes the M1 Abrams cannon so accurate?


Bug Splat
05-17-2010, 11:39 AM
The tide of the war between America and the British was arguably changed due in part to barrels with rifling being adopted by the American fighters. The increased accuracy was unlike anything the Brits had seen and many of them (mainly officers:D) fell at ranges thought to be beyond the effectiveness of a rifleman. Rifling is a good thing.

So we have a couple hundred years of trusted mindblowing accuracy using rifled barrels and then somehow we take a step backwards with the tanks and start using smooth bores again. What gives? I know these tanks have some serious accuracy down range and I'm curious as to what the reason is behind this? How are they so accurate using smooth bores?

gun toting monkeyboy
05-17-2010, 11:47 AM
If you are going to spend several hundred to several thousand dollars per round, you can afford to put some serious R&D and quality control into each one. Much more than you would put into a rifle bullet that costs you pennies. That, and a very expensive targeting computer add up to a very accurate round.

elSquid
05-17-2010, 11:48 AM
So we have a couple hundred years of trusted mindblowing accuracy using rifled barrels and then somehow we take a step backwards with the tanks and start using smooth bores again. What gives?

http://en.wikipedia.org/wiki/Kinetic_energy_penetrator

-- Michael

UserM4
05-17-2010, 11:50 AM
"The main weapons for the original M1 battle tanks were 105mm M68A1 Rifled Cannons. These were upgraded for the M1A1 and M1A2 designs to 120mm M256 Smooth Bore Cannons. The 105mm cannons use kinetic energy cartridges containing alloyed depleted uranium. The Smooth Bore Cannons can accept a range of kinetic energy and high explosive anti-tank rounds"

http://www.armedforces-int.com/projects/m1_abrams_main_battle_tank.html

I dunno if that answers your question or not but it's what I found.

BroncoBob
05-17-2010, 11:55 AM
I'll have to ask my son since his mos is 91G

Sick Boy
05-17-2010, 11:56 AM
They can hit a tank-sized or smaller target a few miles away with a round about 2 feet in length. I am not a man to question awesomeness like that.

This seems to explain it pretty well:

http://boards.straightdope.com/sdmb/showthread.php?t=437320

mstlaurent
05-17-2010, 12:01 PM
The reason they went to smoothbores is because of the velocity of the projectiles, not for accuracy. When the projectiles start to go above a certain velocity (the exact number escapes me), they will strip the rifling out of the barrel. (The APFSDS round on the Abrams comes out at about 5,700 fps, for example.) So they changed to a smoothbore cannon and created fin-stabilized projectiles that didn't need rifling to be accurate. Going with fin-stabilized rounds also allows you to go with a longer, thinner penetrator that will yield better penetration.

The reason it is so accurate is because of the computer. The ballistics computer takes everything into account. Everything. Laser rangefinding, air pressure, wind speed and direction, those are just the beginning. It has a device on the barrel that measures the barrel deflection due to uneven heating, stress, etc. It takes into account the rotation of the earth at their current latitude. All that data lets it put the round right where the crosshairs say it will go. That's the really impressive part.

Suvorov
05-17-2010, 12:37 PM
The reason they went to smoothbores is because of the velocity of the projectiles, not for accuracy. When the projectiles start to go above a certain velocity (the exact number escapes me), they will strip the rifling out of the barrel. (The APFSDS round on the Abrams comes out at about 5,700 fps, for example.) So they changed to a smoothbore cannon and created fin-stabilized projectiles that didn't need rifling to be accurate. Going with fin-stabilized rounds also allows you to go with a longer, thinner penetrator that will yield better penetration.

The reason it is so accurate is because of the computer. The ballistics computer takes everything into account. Everything. Laser range finding, air pressure, wind speed and direction, those are just the beginning. It has a device on the barrel that measures the barrel deflection due to uneven heating, stress, etc. It takes into account the rotation of the earth at their current latitude. All that data lets it put the round right where the cross hairs say it will go. That's the really impressive part.

Pretty much covers it. One other thing is that HEAT rounds loose effectiveness when they are spinning and fin stabilized projectiles do not need to be spin stabilized so rifling is counter productive to both types of munitions. Smooth bores also allow for a better seal and thus more velocity. The lack of rifling will also mean a longer tube life. The Russians and Britts had been using smooth bore guns since the 1960s, us and the Germans were relative late comers to the party.

When the gunner (or commander) engages a target, he will place the reticle on the target and then lase the target. This laser will give the ballistics computer a range to target. The computer will then take the range data plus such variables such as cross wind, barometric pressure, outside air temperature, ammunition tempurature, vehicle cant, and gun turret slew speed (which is a measure of how fast the target vehicle is moving in relationship to the tank), and come up with a ballistic solution. The cannon will then move inducing lead and hold over based on the ballistic solution. The gunner then has only to make sure the reticle is still on the target and fire. The ballistic computer also will correct for such things as barrel wear, and measured ammunition lot variances. As mentioned, a Muzzle Reference Sensor (MRS) will measure for any warp in the gun tube due to unequal heating of the tube and this information is fed to the ballistic computer periodically.

The fire control system is only half of the matter. The other part is the suspension and stabilization system. The suspension on the Abrams allows for an incredibly smooth ride over rough terrain. It really rides like a cadilac. The turret and gun is stabilized on all three axis by multiple gyroscopes that along with the hydraulic system will allow the gun tube to stay "locked" on a target while the hull of the tank undulates underneath it.

The Abrams is truly an awesome vehicle!

Bug Splat
05-17-2010, 12:39 PM
Ah so it does use fins. There is my answer. No doubt it has an amazing computer but even the best computer in the world can turn a slug round shot out of a shotgun into a precision round. I had high doubts about the projectile being a typical bullet design but just did not know. Its amazing that they can push a round that big that fast. I fully understand the reasoning behind going smooth bore with rounds moving that fast. I don't know any rifling that could stand up to many shots at that speed.

Anyone have any pics of the different rounds outside of their sabot?

So my next question is an obvious one..... why don't we have small rifles made like this? I'd think that a rifle shooting a small projectile lets say in the 100gr to 200gr size moving at 6000fps wouldn't be at least an interesting idea. Sure rounds would cost a bit more but look at some of the crazy prices for other long range rounds like the 408 or the 416.

Manic Moran
05-17-2010, 1:45 PM
The Russians and Britts had been using smooth bore guns since the 1960s

I would correct that. The British still use rifled cannons in their tanks, and barring one or two demonstrators have never fitted a smoothbore. For what it's worth, they also hold the record with the world's longest-ranged tank-on-tank kill (5,300m), though as it was with a fin round, the rifling was irrelevant.

The vast majority of Suvorov's post is otherwise, correct, however. You have greater efficiency from a smoothbore, and cheaper costs of manufacture and maintenance. Even the kinetic energy rounds fired from rifles are fin stabilised these days, and are fitted with a slip ring to prevent the round from spinning in the barrel.

However, the downside is that though you have a better tank destroyer, you actually end up with a slightly less capable tank in the traditional sense: For any rounds which require a warhead, such as smoke, high explosive, squash head or white phosphorous, you have to sacrifice capacity and size of round in order to leave space for the fins and the air to act upon them. A traditional spin-stabilised round will carry about 30% more explosives then a fin-stabilised one, for example. Plus, particularly with the slower speeds that these rounds fly at, they become less accurate at range as the fins provide a nice big surface area for winds to act upon and cause great yaw. (Trivia: When firing a fin round in a crosswind, the tank aims with the wind, not into it. As the crosswind acts upon the fins, it pushes the rear of the round away causing the round to fly in a curve back into the wind). This is why artillery cannon are still rifled: To be accurate at range and also have as large a capacity as possible, they can't afford the fins.

Now, if you want a really odd little one, some French armoured vehicles such as the EBR-90 had rifled cannons with no twist to them at all. They primarily fired HEAT rounds.

This is the current-service US Army sabot.
http://upload.wikimedia.org/wikipedia/commons/e/e0/120mm_M829A2_APFSDS-T.jpg

The predecessor, M829A1.
http://www.tonyrogers.com/images/weapons/sabot_120mm.jpg
http://www.fas.org/man/dod-101/sys/land/m829-2.jpg

Not all finned rounds are saboted.
HEAT
http://www.inetres.com/gp/military/cv/weapon/120mm/120mm_M830_HEAT-MP-T.png

why don't we have small rifles made like this? I'd think that a rifle shooting a small projectile lets say in the 100gr to 200gr size moving at 6000fps wouldn't be at least an interesting idea

What's it going to do at the other end? You'd get a 100gr or 200gr perfect tunnel at short range. Flechette rounds for rifles and machineguns (Which effectively means 'sabots' do exist, but unless you're punching through armour, they have little purpose.

Plus you have the problems at extended range of accuracy: We don't have inbuilt ballistic computers to calculate crosswind variance...

NTM

saber
05-17-2010, 3:44 PM
There is some small arms ammo that uses sabots:

http://en.wikipedia.org/wiki/Saboted_Light_Armor_Penetrator_(SLAP)

Bug Splat
05-17-2010, 3:46 PM
I would imagine some of these long range guys would LOVE to have a round that would drop only 6-8 feet at 1000 yards. Talk about a laser! F-class and tactical guys would be all over this. And with the speed comes more wind bucking ability. Sure there would have to be some R&D on this like anything new but this has got to turn on more shooter than just me. :D

smle-man
05-17-2010, 3:49 PM
Remington accelerator rounds are sabot rounds.

Bug Splat
05-17-2010, 3:59 PM
Sure there are Sabot rounds out there for rifles but i'm talking scaled down replica of the Abrams cannon. Smooth bore, finned round, 5500-6000fps. A standard 22cal bullet tucked in a sabot is not going to fly correct or accurately out of a regular rifled barrel designed to shoot normal rounds. Barrel twist is going to be WAY off and you still are restricted in speed by the rifling.

God Bless The Mauser
05-17-2010, 4:08 PM
I believe the gun is German, it's the same one they use on their tanks. They have a history of good tank technology.

Once A Marine
05-17-2010, 4:18 PM
Sure there are Sabot rounds out there for rifles but i'm talking scaled down replica of the Abrams cannon. Smooth bore, finned round, 5500-6000fps. A standard 22cal bullet tucked in a sabot is not going to fly correct or accurately out of a regular rifled barrel designed to shoot normal rounds. Barrel twist is going to be WAY off and you still are restricted in speed by the rifling.

Because shooting at steel and composite armor measured in multiples of inches is completely different than shooting at flesh and bone. To kill a tank, you need a very hard, hypervelocity round to bore through armor and create a plasma burst/overpressure to kill the men inside.

You need a soft metal projectile that can expand on contact and penetrate just right to effect the greatest possibility of a kill on a human target. A hypervelocity needle against a human target will just punch right through.

Suvorov
05-17-2010, 4:19 PM
I would correct that. The British still use rifled cannons in their tanks, and barring one or two demonstrators have never fitted a smoothbore.

Well, if there is anyone here who can sharp shoot me, it is you! ;)

And all this time I thought the Chieftain and Challenger were smooth bored :o

xibunkrlilkidsx
05-17-2010, 5:21 PM
There is some small arms ammo that uses sabots:

http://en.wikipedia.org/wiki/Saboted_Light_Armor_Penetrator_(SLAP (http://en.wikipedia.org/wiki/Saboted_Light_Armor_Penetrator_%28SLAP))

guy i worked with saboted 308 diameter tungsten rod into a 50bmg casing for use in the m2.

as well as a bunch of other misc saboted rounds. i can ask him tomorrow at work. he worked on these kind of things.

Manic Moran
05-17-2010, 5:22 PM
Well, if there is anyone here who can sharp shoot me, it is you! ;)

And all this time I thought the Chieftain and Challenger were smooth bored :o

Nope, sorry. They've been using a 120mm rifle since the 1955 Conqueror, though the 1966 Chieftain L11 uses different ammo. Chieftain and Challenger both used the L11 rifle with three-piece ammo, Challenger 2 uses the L30. L11 ammo could be fired from the L30, but for pressure reasons you had to be careful about going back the other way.

Where they did have the lead with the Soviets, and you might have confused this, is in the use of a 'large' calibre for the standard tank: The British were ditching the L7 105mm rifle about the same time the US was placing the L7 into service as the M68 to replace the 90mm T54. It was some 15 years before the Germans were next to go to a large calibre (Excluding the M60A2 here).

NTM

Bug Splat
05-17-2010, 9:13 PM
Because shooting at steel and composite armor measured in multiples of inches is completely different than shooting at flesh and bone. To kill a tank, you need a very hard, hypervelocity round to bore through armor and create a plasma burst/overpressure to kill the men inside.

You need a soft metal projectile that can expand on contact and penetrate just right to effect the greatest possibility of a kill on a human target. A hypervelocity needle against a human target will just punch right through.

Well I meant more for just target shooting. Doesn't matter what you fire at paper, it will make a hole.

mstlaurent
05-18-2010, 7:45 AM
A standard 22cal bullet tucked in a sabot is not going to fly correct or accurately out of a regular rifled barrel designed to shoot normal rounds. Barrel twist is going to be WAY off and you still are restricted in speed by the rifling.

They actually did just this with tank cannon rounds in WWII, google APDS. They still use this for smaller rounds, they just design the barrel to impart the proper spin on the sub-projectile and don't shoot anything except saboted rounds out of it.

Because shooting at steel and composite armor measured in multiples of inches is completely different than shooting at flesh and bone. To kill a tank, you need a very hard, hypervelocity round to bore through armor and create a plasma burst/overpressure to kill the men inside.

You need a soft metal projectile that can expand on contact and penetrate just right to effect the greatest possibility of a kill on a human target. A hypervelocity needle against a human target will just punch right through.

Unless you're fighting troops that are equipped with ceramic rifle plates, in which case an AP saboted round starts to sound pretty good. Wait, did I just hear an arms race starting?

gn3hz3ku1*
05-18-2010, 7:53 AM
you guys are all WRONG! they have a magpul designed trigger.

mif_slim
05-18-2010, 8:08 AM
http://www.fas.org/man/dod-101/sys/land/m829-2.jpg
NTM

Are those RL-15 powder or Varget? It has to be Varget. it burns cleaner. :P

Those powder's gotta be fist size! and the BC gotta be up in the hundreds!! LOL

tonelar
05-26-2010, 8:31 AM
I've shot sabot rounds out of my 12 on a couple of occasions. I did notice they hit higher on the target than the standard slugs did. Also they grouped a little tighter, but I was only shooting at # 50 yards and my target was an old maytag.

xrMike
05-26-2010, 8:56 AM
Are those RL-15 powder or Varget? It has to be Varget. it burns cleaner. :P

Those powder's gotta be fist size! and the BC gotta be up in the hundreds!! LOLHehehe, first thing I thought when I saw that pic: "That powder would probably not meter well in my ChargeMaster..." :D

orangeusa
05-26-2010, 9:01 AM
mstlaurent pretty much nailed it . Droop measurement and fire control system are most of it...IMHO.

I was at Aberdeen Proving Grounds when the 120mm was being tested for deployment. At that time, there was no barrel "droop" measurement and it WORKS.

We (Rockwell/Delco prototype tank) were firing using a milli-meter radar for targeting - actually slewed the turret. The tank had a prototype droop measurment (laser bounced off mirror on front of barrel). Our groups were the best ever measured at APG (per the Captain in charge of our project).. The M1A1 was not near as accurate back then....

Later, I heard the barrel measurement was added to M1. It's hard to believe, but the barrel was moving up to 1/2" due to temperature, number of rounds through the barrel and if cold barrel or after firing. Compensating for that makes a big difference at "those" kind of distances...

Don't know much about the rounds - the demo fired aluminum rounds (easier on the drone M48 tanks used as targets).

.

basalt
05-26-2010, 9:34 AM
Hehehe, first thing I thought when I saw that pic: "That powder would probably not meter well in my ChargeMaster..." :D

I thought it looked like they filled it with D-Con or Alfalfa pellets!

Notblake
05-26-2010, 10:26 AM
I could be totally wrong here, but I don't believe that fin-stabilization works very well if the fins are only .2 " in diameter. It also raises the question, "How much money do you want to pay per round?" when there are so many working traditional rounds out there.

reidnez
05-26-2010, 11:15 AM
I could be totally wrong here, but I don't believe that fin-stabilization works very well if the fins are only .2 " in diameter. It also raises the question, "How much money do you want to pay per round?" when there are so many working traditional rounds out there.

That is basically the conclusion the military came to when it evaluated flechette rounds with project SALVO. The flechettes were potentially very flat-shooting and long-ranged, but the light weight and hyper velocity also made them incredibly unstable. There were some reports of flechettes being deflected totally off-target by light foliage and even rain. Also, while they were excellent at penetrating armor, but didn't always do much damage once they did penetrate--since by design they did not expand or fragment.

X-NewYawker
05-26-2010, 11:19 AM
http://i125.photobucket.com/albums/p54/Fasanoland/US%20Army/Abrahms-tank.jpg

orangeusa
05-26-2010, 11:33 AM
love the "Gutter Ball" on barrel.. :)

Group B
05-26-2010, 12:24 PM
I believe the gun is German, it's the same one they use on their tanks. They have a history of good tank technology.

Ze Germans!

Yes, the 120mm gun was developed by Rheinmetall AG.

Manic Moran
05-26-2010, 12:45 PM
The Abrams is one of those multinational things... My tank had a German cannon, British armour, Canadian fire-control-system, Belgian machineguns, American engine, Italian sidearms, and an Irish commander.

NTM