Abrams, 120 mm cannon accuracy?
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#1: Abrams, 120 mm cannon accuracy? Author: Skeet,  PostPosted: Mon May 15, 2006 7:12 pm
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The Abrams carries a 120 mm non-rifled cannon. I understand the non-rifled cannon allows a shaped charge projectile to function better, but it also seems to be able to hit targets waaaaaaaaaaaaaaaay out there.

How's it do that?
#2: Re: Abrams, 120 mm cannon accuracy? Author: Joe_D, Location: Razorback Country PostPosted: Tue May 16, 2006 3:26 am
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Skeet,
I can name two basic changes. Modern fire control systems that compensate for variables such as Range, Air Temp, Barometric pressure, Ammo temp, Cant, Lead, etc. coupled with ballistic solutions that can be calculated for individual type rounds within 1 meter using this data. All is done with the gunner pressing a lase button. The other is that almost all modern tank rounds are fin stabilized and do not need to be spun to stay accurate. Even the old 105mm rifled guns eventually fired primarily fin stabilzed rounds. Quality of production also reduces round to round dispersion within round types allowing longer more accurate engagements too. I guess that makes three. I can write pages of what has been done in the last 30 years to improve accuracy, but basically what modern electronics has done for automobiles pretty much applies to tanks.

Joe D
#3: Re: Abrams, 120 mm cannon accuracy? Author: mike_Duplessis,  PostPosted: Tue May 16, 2006 5:21 pm
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I dimmly recall in the early 80s someone (the British?) held a competition to see which gun they were going to choose for their next generation tank. They used the standard 105mm gun as a baseline for comparison, firing its APFSDS round. To everyone's horror the 105mm solidly outperformed all the modern technology 120mm contenders as far as accuracy went. It seems even with driving bands a 105mm APFSDS round would still be given a slight rotation. Apparently this was enough to turn any tendency to drift into a corkscrew path as the dart flew downrange. - I hope I'm recalling this story correctly.

Rheinmetall in particular didn't like the results of those tests. It's possible this embarrassment in trials drove much of the insane standards in modern fire controls. Everything from tube wear to weather to propellant temperature is thrown into the mix.
#4: Re: Abrams, 120 mm cannon accuracy? Author: mike_Duplessis,  PostPosted: Tue May 16, 2006 6:47 pm
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I have a dumb question.
I read somewhere how when firing the Russian 125mm gun the ballistics calculations are adjusted according to propellant temps. I also read somewhere that one flavor of Merkava or another includes temperature-controlled ammo storage to maximize performance (or more accurately, to avoid degradation). At least at one point Israeli 120mm gun ammo was quite temp-sensitive.

Here's the dumb question - What about Abrams? How do they monitor propellant temps? Is that rear turret bustle temp-controlled at all? or is it monitored by a themostat in order to automatically adjust ballistics computations? I believe for T-72s they'd simply take an air temp reading in the morning and use those calculations all day (yesterday was -8 c, today its +40 c).
#5: Re: Abrams, 120 mm cannon accuracy? Author: Dontos, Location: Vine Grove, KY PostPosted: Tue May 16, 2006 9:40 pm
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- mike_Duplessis
....Here's the dumb question - What about Abrams? How do they monitor propellant temps? Is that rear turret bustle temp-controlled at all? or is it monitored by a themostat in order to automatically adjust ballistics computations? I believe for T-72s they'd simply take an air temp reading in the morning and use those calculations all day (yesterday was -8 c, today its +40 c).


No such thing as a dumb question....

Actually there is an ammo temp gauge in the turret. One simply input temp into FCS and the 'little hamsters in the white box' ( Shocked - Just kidding on the hamsters...) calculates the ballistic solution with all inputed info.

Ammo 'wells' seem to run much cooler than crew compartment. Ammo doors block out residual heat from turret & outside.

Many times (as am M-1, IPM-1, & M1A1 gunner) I remember temps in ammo wells running in 100-120 degree range. Ft Polk actually seemed to be the worst.

Don
#6: Re: Abrams, 120 mm cannon accuracy? Author: Dontos, Location: Vine Grove, KY PostPosted: Tue May 16, 2006 9:48 pm
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- mike_Duplessis
I dimmly recall in the early 80s someone (the British?) held a competition to see which gun they were going to choose for their next generation tank. They used the standard 105mm gun as a baseline for comparison, firing its APFSDS round. To everyone's horror the 105mm solidly outperformed all the modern technology 120mm contenders as far as accuracy went. It seems even with driving bands a 105mm APFSDS round would still be given a slight rotation. Apparently this was enough to turn any tendency to drift into a corkscrew path as the dart flew downrange. - I hope I'm recalling this story correctly.

Rheinmetall in particular didn't like the results of those tests. It's possible this embarrassment in trials drove much of the insane standards in modern fire controls. Everything from tube wear to weather to propellant temperature is thrown into the mix.


Mike

In 1988 'we' had some serious problems with the 120mm ammo. Initially it was packaged, shipped, and delivered in wooden crates like the 105 ammo. This caused serious preformance reliability problems.

When 'we' were doing CAT 89 train up, we found that round to round dispersion was way off the scale. 'Our' goal was to hit a coke can at 1500m. With the first generation (training) Sabot, it was difficult to hit the Screening panels at 1500m with more than one round, let alone a coke can.

After 'much pain' it was finally determined that the ammo was at fault. This is about the time that the sealed 'catacomb' containers made their appearence.

Voila!!! We started screening and hitting a 12 inch 'bulls-eye' at 1500m, round after round.

Don
#7: Re: Abrams, 120 mm cannon accuracy? Author: Joe_D, Location: Razorback Country PostPosted: Wed May 17, 2006 12:33 am
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Hey Dontos,
Yeah, there were some issues with the old M865 anyway when it first came out. With the newer PA-116 (I think that's what they're called)containers you probably got the newer M865IP (PIP) or whatever they called it then. We used to have to ID it from the older ones by the groves cut in the petals. Both had the same ID and DODIC. I think we are on our 4th or 5th connotation of the M865 now.
Mike, gotta remember that unless you are firing service ammunition results may vary. Training ammo has to be good but the other factor is cost as opposed to service rounds where money doesn't factor in that much. I can believe the 105 was more accurate during the test just because the rounds for the 120mm were not a mature of a system at that time. My experience with 105 training APDS compared to 120 training APCSDS was that the 105 seemed more accurate. I will tell you when they screened service rounds in Kuwait prior to the war (OIF) the results we most impressive, especially the shot groups. 1st UK didn't screen, they zero'd using L29 and then switched to L27 CHARM. Fired a lot more ammo but I personally believed they had a more accurate final result. They do have some impressive long range gunnery ability.

Joe D
#8: Re: Abrams, 120 mm cannon accuracy? Author: Dontos, Location: Vine Grove, KY PostPosted: Wed May 17, 2006 1:04 am
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PIP...thats it.

I believe it had a lot number of '88F' the only APCSDS-T that we were allowed to use.

In the days prior, (CAT89) we zeroed every different lot we got. 5 rounds. Fire 3 at 'bull', determine MPI, toggle adjust, then fire 2 confirmation rounds. No 'Fleet Zero' for us.

(I still have my zero data from May - June 89.... I'm NOT a 'pack-rat' damn it!!!) Laughing

Of course, that was 'E-ONS' ago.... Cool

#9: Re: Abrams, 120 mm cannon accuracy? Author: Joe_D, Location: Razorback Country PostPosted: Wed May 17, 2006 2:30 am
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Dontos,
I still think that zeroing is better than screening Smile , but of course money talks Rolling Eyes . The theory is that if all tanks were made and maintained to a equal level of quality and the ammunition was constructed within certain tolerences than one could reasonably expect the same firing results across the board. Screening just verifies that the tank and ammo meet these tolerances. It may not be the most accurate but the standard is 2 rounds within the circle of the ST-5 panel (formerly ST-4 octogon). If it can accomplish this it meets the accuracy requirements. The problem with zeroing is you can potentially hide a maintenance problem Sad . Just because you can adjust the reticle to get a bulls eye at 1500 meters doesn't mean you can do the same thing at 1000 or 2000. The FCS could be flawed and not correctly calculate the ballistic solution. All you accomplished was make it hit at 1500 meters standing still. Other factors are also mechanical. It can be very frustrating with older systems Evil or Very Mad .That's the reason why Master Gunner's look the way they do on a range. But..., if the tank is good and the ammo is good, zeroing is far more accurate Wink . All comments made are my personal opinion and do not reflect any official doctrin or procedures

Enjoy the Armor conference
Joe D
#10: Re: Abrams, 120 mm cannon accuracy? Author: Skeet,  PostPosted: Sun May 21, 2006 10:00 am
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Thanks folks.

In reply to another question I made, this link was provided:

www.globalsecurity.org...m830a1.htm

That pretty much answers my question. I didn't know that that all the 120mm rounds were fin stabilized.

Interesting idea about using that round being used on helicopters. I wouldn't think you could bring a 120 mm to bear on such a target.
#11: Re: Abrams, 120 mm cannon accuracy? Author: Roy_A_Lingle, Location: El Paso & Ft Bliss, Texas PostPosted: Sun May 21, 2006 6:50 pm
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HI Skeet! Hi Folks!

- Skeet

Interesting idea about using that round being used on helicopters. I wouldn't think you could bring a 120 mm to bear on such a target.


That idea has been around for bit. The MPAT round makes it work a lot better.

Sometime around 1972-73, when I was stationed at Hunter Liggett Military Reservation, the unit I was in conducted a test to see if it was possible for Soviet Tanks to engage US Cobra Attack Helicopters firing Sabot ammo. The unit had five platoons of M60A1 tanks which were fitted with a Soviet type of sight retinal. Using the Great Grand Father version of the system used now days at the NTC, it was learned that Soivet's Tanks using Sabot could not hit a moving Cobra most of the time.

After the test was over, then some one asked the question, "Can US tankers using our current FCS and Sabot, hit a Soviet gunship"? Back to range with the nomal sight retianls reinstalled. It was found that our system could nail a hovering or slowly moving helo. Last I heard of that test program was they where going someplace else to try and learn how much damage a Sabot round could do to a helicopter. I wonder if somewhere in the developement of MPAT round, those old tests had anything to do with it's design?

Some of my old history.
Sgt, Scouts Out! Smile
#12: Re: Abrams, 120 mm cannon accuracy? Author: mike_Duplessis,  PostPosted: Mon May 22, 2006 12:55 pm
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I recall reading somewhere (warning, I may be remembering this all wrong) that German tanks were slated to get a 'dual-purpose' laser rangefinder for combatting helicopters. I believe the article said - and I'm really shakey on this info - that a laser reflection can give multiple range returns due to laser scatter. A standard ground combat rangefinder will, I think, discard all but the last return. This is the opposite of what you want for a helicopter which would be primary laser return followed by background clutter. So I think the article said the German rangefinders had a switch that would allow either accepting last or first laser return depending on the target type.

What this implies is a helicopter close enough to be within the APFSDS dart's flat trajectory would be dead meat, but if ballistics calculations are involved (beyond 2500m?) then hit probability may be hindered by the ground-optimized ranging equipment.

Any REAL tankers willing to help me on this?
#13: Re: Abrams, 120 mm cannon accuracy? Author: Dontos, Location: Vine Grove, KY PostPosted: Mon May 22, 2006 3:13 pm
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- mike_Duplessis
I recall reading somewhere (warning, I may be remembering this all wrong) that German tanks were slated to get a 'dual-purpose' laser rangefinder for combatting helicopters. I believe the article said - and I'm really shakey on this info - that a laser reflection can give multiple range returns due to laser scatter. A standard ground combat rangefinder will, I think, discard all but the last return. This is the opposite of what you want for a helicopter which would be primary laser return followed by background clutter. So I think the article said the German rangefinders had a switch that would allow either accepting last or first laser return depending on the target type.

What this implies is a helicopter close enough to be within the APFSDS dart's flat trajectory would be dead meat, but if ballistics calculations are involved (beyond 2500m?) then hit probability may be hindered by the ground-optimized ranging equipment.

Any REAL tankers willing to help me on this?


Mike

I 'used' to be a REAL Tanker, so I'll try to take a stab at explaining this....

The Abrams LRF has dual settings for '1st return' & 'Last return'.

If lasing on a target on a hill top (or in the air) with a limited possibility of any obstructions then this means the LRF will give a range to the actual target.

Many times multiple range returns are noted due to tree limbs, grass, (etc) that are in the line of sight between the tank and the intended target. When in 'Last Return' the indexed range should be the target you are lying the reticle on.

There is a 'multiple range return' bar in the symbology of the GPS which lets the gunner know that more than one range return has been received. Its up to him to assess if the indexed range seems appropriate.

Hope this helps,
Don
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