Tank Gun Accuracy

[rexford]

Main factors influencing accuracy are:

1. VELOCITY

high velocity flattens trajectory, since round moves further for same gravity drop. flat trajectory means that when range estimate is in error (most are), height of round doesn't change as much so probability of a hit stays high.

2. WEIGHT

Softballs can be thrown many times further then a ping pong ball even though ping pong is smaller and lighter. Heavy things carry better due to momentum which requires less velocity loss for same energy loss.

3. NOSE SHAPE

Uncapped rounds are pointy but not too pointy so they don't break and bend on angled hits. ballistic caps (BC) lower air resistance, so BC rounds lose velocity and penetration slower than uncapped AP if other things are equal.

4. DISPERSION or SCATTER

Jentz' figures are hit % when range estimation error is zero (almost never happens) and percentage is number of scattered shots within a given shape. Scatter is usally secondary to other factors, except in case of APDS where high velocity and flat trajectory were ruined by highest scatter of any round during WW II (not every shot, but enough to have Jentz call WW II APDS "not particularly accurate".

5. WEIGHT TO FRONT AREA RATIO

Weight is carrying power (remember ping pong balls), diameter squared is indication of air resistance. 76 HVAP carries tungsten sabot in big lightweight carrier, 76mm APDS discards sabot and flies with about same weight as 76 HVAP tungsten but alot smaller diameter. Result, 76 APDS loses velocity a heck of alot slower than 76 HVAP.

76 HVAP will be more accurate than 76 APCBC at long range due to flatter trajectory, even after faster velocity loss is considered because HVAP starts at 3400 fps, APBCB at 2600 fps.

152mm APBC has 108#/6"squared, for 4.2.

37mm APCBC has 1.92#/1.5"squared, for less than 0.9.

Velocity alone doesn't but accuracy, APDS scatter spoils things. But small scatter doesn't buy accuracy either. 75L24 may have same scatter as 88, but 75L24 trajectory is so curved that a 50m range estimate error at 500m may result in a miss, while one aims the Jagd Tiger 128mm at 900m range and hits everything inbetween because trajectory is so flat.

Jentz' figures are not field accuracy, they just tell one how wide the scatter is if the aim is kept constant. That's all dispersion probabilities mean. They don't suggest the accuracy on the second or third shot, because the third shot at 1500m may not have the range setting close to target range, so scatter won't be centered on the target but on some point outside the target.

Dispersion is part of the accuracy picture, and it limits max hit % at 2000m and 3000m and 4000m. If one has a gun sight that exactly predicted range out to 5000m but 50% of the constant aim shots at 5000m were greater than 2m from hit center, 5000m hits would be rare.

Heavy rounds like 152mm APBC carry well but are shot at slow speed (600 m/s) and the rate of fire is about 1.5 shots per minute. 100mm APBC weighs about 34# and is fired at 900 m/s, but rate of fire is also lower than a 75mm gun. 122mm on IS might shoot at 1 to 2.5 shots per minute, although a 55# APBC round shot at 2600 fps will carry alot of energy to 2500m and beyond.

Steel has a difficult time holding together above 3000 fps, tungsten resists high velocity better and small tungsten cores can outpenetrate big steel plugs without all the recoil, which increases the penetration that a given gun can obtain.

Tungsten has bad slope effects because high hardness brings with it brittleness 76 APCBC or 17 pounder APCBC has 2.5 slope multiplier against Panther glacis, 80mm at 55° from vertical is equivalent to 200mm at 0°.

Tungsten HVAP has 4.3 slope multiplier against Panther 80mm glacis, for 344mm at vertical equivalent resistance. HVAP may outpenetrate 76mm APCBC, but 55° Panther glacis has 1.72 times the resistance against HVAP!

German APCR used to stick in the guns, according to Jentz. And rounds were so light and carrier was so large that accuracy and penetration fell off rapidly with range.

Accuracy depends on alot of factors and velocity, or scatter or penetration alone can be misleading in certain cases.

[:USERNAME:]

http://www.warlinks.com/equipment/tank_research/section_c.html

[Bullethead]

rexford said:

<BLOCKQUOTE>quote:</font><HR>Accuracy depends on alot of factors and velocity, or scatter or penetration alone can be misleading in certain cases.<HR></BLOCKQUOTE>

You listed all those technical factors, but you omitted the most important factor of all--the gunner.

You seem to assume that a given gun firing a given ammo will always either hit or miss depending on some mathematical formula. This might be true for a static gun bolted to a test frame firing at a paper target at a fixed range.

However, this is NOT true when there's a gunner with control over the piece. Therefore, IMHO, most of the technicalities you mention here have very little bearing on how the gun will perform in combat with somebody behind the sights who can actively compensate for the gun's performance.

The worst gunner can always manage to make the most accurate gun miss. And vice versa.

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-Bullethead

In wine there is wisdom, in beer there is strength, in water there is bacteria.

[This message has been edited by Bullethead (edited 01-19-2001).]

[Matthew_Ridgeway]

Conversely the best riflemen in the world couldn’t hit the broad side of a barn at 200 meters with a Brown Bess.

[rexford]

True about gunner factor, the post was discussing how projectile and gun factors fed into the equation.

Having someone who aimed true and someone else who estimated range well could do wonders. Alot of factors. Yup!

[Bullethead]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Matthew_Ridgeway:

Conversely the best riflemen in the world couldn’t hit the broad side of a barn at 200 meters with a Brown Bess. <HR></BLOCKQUOTE>

Remember that muskets had no rear sight graduated for different ranges. Also, back in the days of the musket, a soldier's skill was rated on his ability to perform the steps of loading his weapon and marching in formation. His firing training was rigidly confined to firing exactly parallel with the ground regardless of range (nobody back then except artillerymen paying any attention to ballistic trajectories), and the sergeants made sure he developed muscle memory for this point of aim by using his spontoon to keep his squad's muskets from pointing up too high.

So the ball starts out about 5' above the ground (shoulder height). It then accelerates downward just like any other falling object. Thus, a ball fired parallel to the ground from about 5' up will hit the ground about 1/2 second after it was fired. (D = 1/2A(T^2) + VoT + So)

The horizontal distance the ball travels is thus a function of its muzzle velocity and how far it can go in that 1/2 second before it hits the ground. Muskets fired subsonic balls, so assume a max muzzle velocity of 1000fps. Ignoring speed loss in flight, this means the ball would only travel 500' before hitting the ground. Thus, because 200m is over 600 feet, the ball would hit the ground due to ignorance of ballistics long before it reached the broad side of it, even assuming probably a higher-than-actual muzzle velocity.

Thus the oft-cited statement above, solidly based on both mucho battle experience and contemporary tests by trained troops at battalion-sized paper targets, fails to appreciate the fact that given the marksmanship training of the day, 200m was simply beyond the ABSOLUTE, not just the effective, range of the musket. The fact that a few hit were obtained at this range anyway indicates some troops aimed higher than they were supposed to

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-Bullethead

In wine there is wisdom, in beer there is strength, in water there is bacteria.

[This message has been edited by Bullethead (edited 01-19-2001).]

[This message has been edited by Bullethead (edited 01-19-2001).]

[Guest Michael emrys]

<BLOCKQUOTE>quote:</font><HR>Originally posted by rexford:

Main factors influencing accuracy are:

1. VELOCITY

high velocity flattens trajectory, since round moves further for same gravity drop. flat trajectory means that when range estimate is in error (most are), height of round doesn't change as much so probability of a hit stays high.<HR></BLOCKQUOTE>

There are a couple other useful results of a high velocity. One is that for a given range, a faster round will less subject to windage. The other is that it will require less lead for a moving target and thus a reduced chance of misestimating that lead.

Michael