RexMan

I see a Wartgamer (Watgamer?) but I do not see a Lewis that has posted here. Since I personally am looking into dispersion, a naturally non-perfect phenomena, why would you say that about me. Do you feel the need to try to psychoanalyze people without meeting them? Myself, and others, seem to find this interesting. Is there a personality disorder to describe kill-joy negative personality types like yourself? Or are you just obsessed with trying to point out others problems? Sounds to me you might be among the types you are describing!

Dispersion, in direct fire, can be atributed to velocity variation (projectile comes out faster or slower) as well as non-repeatable gun repositioning. If you were to take a sufficiently rigid barrel, put it in a vise, and ensure that the propellant produces the same reaction (along with things like constant friction within the barrel, etc), then a higher velocity projectile from that setup will be more accurate. That is because the exsternal ballistics it experiences will not be the same. For a set rifling, the higher velocity projectile spins faster, the amount of time it is subject to atmospheric conditions is less, etc. By the way, rifling and spin CAN be too much. You want just enough to stabilize the projectile. Too much has an adverse effect just like too little. It will also wear out faster.

Accuracy has to define a target. Thats so basic as to be funny. When trying to hit a house at 200 meters. Most anything is accurate enough.

I think everyone should do the following test (if interested)... Take a 37mm ATG (or any HV HE chucker) and just area target a point about 200 meters. Use a flat terrain test bed. From the small craters, its obvious that horizontal dispersion is not modeled exactly. From my testing, the placement is way too close.

Then try defining effective if you can not define accuracy.

US tank gunnery indirect fire: The reason I bring up the US tank gunnery emphasis on indirect fire techniques is because it may actually reveal something about the gun system itself. If you have a small target like a 1 meter by 1 meter antitank gun at 3500 meters, thats a sub-mil target. It may actually be at the limit of aiming of the weapon. The actual fine corrections that can be dialed in is what I am speaking about. In technical terms this is called resolution. You actually must have even better resolution to adjust aim after initial aiming. Typically a factor of 10 would be good and a factor 0f 5 maybe acceptable. In addition: US tank gunnery policy for the 75mm ordered HE against tanks at ranges over 2000 meters. I am not so sure this is due to failure to penetrate as much as failure to actually hit the target. Surely a 75mm AP round can destroy many vehicles with a side hit at this range? It is a branch off the discussion but still within cherry tree.

Again, Unless a person understands that there is vertical dispersion and horizontal dispersion, there is no need to discuss accuracy. You are throwing the word accuracy around without recognizing one of the most fundamntal aspects of this discussion. As food for thought (for those that can eat) try to understand this.. An antitank gun is accurate when attacking tanks yet inaccurate when attacking a trench. Tank and trench are both at 500 meters.

Until people here can grasp the difference in vertical dispersion and horizontal dispersion, there is no point about discussing accuracy.

Except you were assuming an exposed turret crew? Could you also explain what this is about? You just finished saying there is no correlation between accuracy and velocity (hah!) and now you want to calculate energy at target? Why? [ July 07, 2005, 04:45 PM: Message edited by: RexMan ]

Poorly placed? Worse than your FlaK contribution?

..and much of that has nothing to do with hitting a vertical target like an antitank gun shield.

And tanks generally do not have the elevation required to use upper register.

Muzzle energy is easily calculated as 1/2*mass*velocity^2. The sherman smoke shell is actually a HE shell filled with some type of smoke producing chemical and a small HE core. The mass is not that much different than a HE shell. You are also incorrect regarding twist and spin. A higher velocity gun does not need an agressive twist to get the same amount of spin. [ July 07, 2005, 03:04 PM: Message edited by: RexMan ]

You are probably confusing accuracy with something else as well as confusing the accuracy of hitting vertical targets vs. horizontal targets. And as far as 'so?'. Can you care to expand on that? Or what you are 'soing' about?

The US 75mm armed shermans did not fire a smoke round with 12% of the muzzle energy (do you mean velocity?) of any AP round they fired. It is not quite the amazing feat that you imagine. I can get the actual muzzle velocities for all the US 75mm rounds if you like.

The US Army made quite a practice of using HE at long range from tanks in a indirect mode. They mention it at length in training manuals and German reports speak of great quantities of HE being used against them at maximum ranges. Terrain, of course, could rule this out but given the opportunity, shermans would bombard ATG at great ranges. The US tanks had gunner's quadrants it seems.

Accuracy is relative. Low velocity adds some advantages - particularly in terms of adjusting and terminal ballistics. </font>

This data is very revealing (even though it is more than likely for solid shot type AP rounds). It shows that height is a very strong factor in obtaining hits on 'vertical' targets. The reader show note that this is for a known range. A major concern in battling antitank guns is knowing the range. They are very small and not only hard to spot, but very difficult to guage in size and exact position. Many times, especially when they are backdropped against woods/towns, they are nearly impossible to fix on. [ July 07, 2005, 10:52 AM: Message edited by: RexMan ]

Internal Ballistics deals with events happening within the gun barrel. External ballistics deals with events after the projectile has left the barrel and is in flight. Terminal ballistics deals with what happens to the projectile after striking the target (and perhaps exploding). I have to agree with an earlier poster that a high velocity HE shell that detonates nearly parallel to the ground is actually superior in fragmentation effect tha one that is 'nose-down' and detonating. For a 'nose-down' HE shell to be at its best, it must be at a nearly vertical drop. The mortar trajectory approximates this closely. Most direct fire HE weapons can not attain this very high trajectory needed. An even better terminal effect is the air-burst. As far as range adjustment, it is not really applicable to what is being discussed; ie hitting a vertical 'wall' target like a antitank gun shield. But I see the point that a very high velocity gun, trying to hit a small parcel of land (say a trench), would need to have very fine adjustments coupled with low dispersion. Low velocity high-arc shells have dispersion along the line of fire by the way. This has to be taken into consideration. True 'adjustments' have to compare the dispersion to the amount of adjustments. [ July 07, 2005, 08:26 AM: Message edited by: RexMan ]

Just to be clear, I am discussing the hitting of a vertical target with width.

I have read this thread with interest. I do not believe either side made a good case beyond intuition and some assumptions. I would guess that range would have much to do with the matter. Just as it does in many battlefield cases. Not only distance but also the estimation of distance. Take the 88mm gun of the famed Tiger and Flak weapon of the German army. At 1000 meters it had a statistical chance of 50% zone of 27.6 inch in height and 15.h incj in width. About 0.7 meter in height approximately. This is using the data for the AP round. The HE round may not have been as accurate. They have a very close muzzle velocity I believe. Since the shield on many purpose built Antitank guns are only about 1 meter high, getting a hit directly on the gunshield at this range is not an easy task. This is further compounded by any errors due to range estimation, wind effects, etc. If the 88 knew exactly the range, and aimed at the center of the antitank gun shield, its chances of a hit are not exactly assured. Many tank guns specifically designed for WWII (in the later years) purposely designed the HE rounds to have lower velocity than the AP round. In other words, they may not be expected to have as much accuracy as the Tiger I.