No, I'm saying Velocity = Destructive power.
Charged shell/Size also = Destructive power.
An increase in size is directly proportional to a decrease in velocity, unless self-propelled.
Destructive power is the metric by which effectiveness is better.
My point is Velocity > Charge/Size
Infact, many earlier AT shells by all factions were just steel core.
Charge may = velocity - but this is coupled with immense downsides, to the point were charge has to be enormous to equal the destructive power provided by an 88 for example, which utilized high velocity to penetrate.
Also, Increasing velocity is easier than increasing charge, the fact that Soviets preferred charge/shell size over attempting to create the highest velocity is more to do with their doctrine of tank design.
Your example of the German 128mm is good,
If we take the Jagdtiger, which used a 12.8cm pak44
Muzzle velocity 950 m/s (3,100 ft/s)
Maximum firing range 24,410 m (26,700 yd)
"The heavy charge was used when the gun was fulfilling its intended role as an anti-tank gun, where it fired a 28.3 kg APCBC-HE projectile (PzGr.43) at a muzzle velocity of 950 m/s. With the heavy charge, and using the PzGr.43 projectile, the Pak 44 was capable of penetrating 212 millimetres (8.3 in) of 30 degree sloped armour at 500 metres, 200 millimetres (7.9 in) at 1,000 metres (1,100 yd),and 178 millimetres (7.0 in) at 2,000 metres (2,200 yd) range."
-Hogg, Ian V. German Artillery of World War Two.
Compare it to the IS-2 which has the 122 mm D-25 tank gun (a direct descendant of the 122 mm gun M1931/37 (A-19))
Muzzle velocity 806 m/s (2,640 ft/s)
Maximum firing range 20.4 km (12.67 mi)
"The A-19 was primarily used for indirect fire against enemy personnel, fortifications and key objects in the near rear. It was also equipped with armour-piercing shells for direct fire against armoured targets. Although not an ideal anti-tank gun because of its large size, slow traverse and relatively slow rate of fire, in 1943 the A-19 was one of only a few Soviet guns effective against the new German tanks, such as the Tiger and Elefant."
Potapov, V. Was the Tiger really King?
The large 122 mm HE shell was its main asset, proving highly useful and destructive as an infantry-killer. In extremis, the IS-2 engaged enemy heavy armor with OF-471 (Russian: ОФ-471) high explosive projectiles. These shells had a mass of 25 kg (55 lb), a muzzle velocity of 800 m/s (2,600 ft/s), and were equipped with a 3.8 kg (8.4 lb) TNT charge. The explosive power could blow off an enemy tank turret, drive sprocket and tread of the heaviest German tank even if it could not penetrate the armor.
Soviet Heavy Tanks: World War 2 In Review Special,
The Encyclopedia of Weapons of World War II, Chris Bishop, P. 41
This is given due to "evident gradual decline in the quantity of molybdenum (M) in the German T-VI and T-V tanks, and a complete absence in the T-VIB. The reason for replacing one element (M) with another (V, vanadium) must obviously be sought in the exhaustion of their on-hand reserves and the loss of those bases supplying Germany with molybdenum. Low malleability appears to be characteristic of the "Tiger-B's" armor. An advantage of domestic armor, as is well-known, is its high malleability; German armor has fewer alloys and is therefore significantly less malleably."
"D-25 Tank gun". The Russian Battlfield. Retrieved 6 November 2014.
Thus, whilst similar effects can be achieved, in terms of creating destructive power (specifically against enemy tanks) Velocity is indeed superior.
During testing of the weapon, the German KwK 43 tank gun gave good results in both armor penetration and accuracy, practically the same as the Soviet 122 mm D-25 gun on the JS-2 tank. At a range of 1000 metres, the following projectile impact deviations from the aiming point were observed: 260 mm in the vertical, and 210 mm in the horizontal. In comparison, for the JS-2 tank's D-25 gun the average projectile deviation from the aiming point did not exceed 170 mm in the vertical and 270 mm in the horizontal during stationary firing at a range of 1000 metres. The penetration capability of the 71-caliber long 88 mm KwK 43 gun, with its muzzle velocity of 1000 m/s for its armor-piercing projectiles, was 165 mm at a 30 degree impact angle at 1000 metres. In particular, the "Tiger-B" projectile went completely through the turret of its "colleague" at a range of 400 m. But in high-explosive power, the 88 mm projectile was 1.39 times inferior to the 122 mm high-explosive fragmentation projectile.
Potapov, V. Was the Tiger really King?
Therefore it can be seen, that a difference of 1.39 between a German 8.8cm gun and a Soviet 122mm, is negligible, and the effects of the Soviet gun are mainly attributed to a lower quality found in the alloy used for the KT's armour. Despite a much smaller shell, the 8.8cm gun attributes being on par with a 122mm gun to its velocity.
Note, this test uses the inferior PzGr. 39/43 (APCBC-HE)
Projectile weight: 10.40 kg (22.9 lb)
Muzzle velocity: 1,000 m/s (3,300 ft/s)
Rather than PzGr. 40/43 (APCR)
Projectile weight: 7.30 kg (16.1 lb)
Muzzle velocity: 1,130 m/s (3,700 ft/s)
------------------------PzGr. 39/43 (APCBC-HE) ---- PzGr. 40/43 (APCR)
Range in metres ------- 2000 ----------------------- 2000
Penetration in -------- 132 ------------------------ 153
millimetres
Jentz, 1996, p. 9
So, even though PzGr. 39/43 (APCBC-HE) is a 3.1kg more massive shell than PzGr. 40/43 (APCR), its penetration is increased. The Germans recognized that velocity was the "most important" factor, when it came to achieving raw destructive power, let alone all the other advantages provided by a higher velocity gun (range/accuracy/storage capacity, etc). In fact, the British realised the importance of velocity, which was behind the design theory of the British Sherman Firefly and Comet, also the American M4A3E8 - Easy 8. All of these guns used velocity to generate destructive power. This is shown by modern doctrine also. The only disadvantages of higher velocity, is the difficulty in manufacturing (has to be higher quality production and material) and the length of the barrel can make transport and maneuvering in close quarters more difficult.
As to your note about "Velocity was preferred, sure, but it was not as PRACTICAL."
-This is untrue, the Germans used velocity as it was both proven effective and able to be done with a material shortage.
"Anyway, to refocus the discussion, velocity is the goal because of material efficiency, accuracy, loading times, and yes destructive power. Others were pointing out that mass/payload could and did reach the impact on destructive power that velocity had (specifically for the 122mm), which you appeared to attempt to refute."
I was not trying to refute the destructive power of the 122mm gun (Although, I think it was worse).
Due to:-
-The live fire tests were conducted in the fall of 1944 at Kubinka, during the course of which the following results were obtained:-
3. Impacts of 3-4 armor-piercing or high-explosive fragmentation shells from 152, 122, or 100 mm artillery pieces caused cracks, spalling and destruction of the weld seams in the tank's 100-190 mm thick frontal armor plates at ranges of 500-1000 metres. The impacts disrupted the operation of the transmission and took the tank out of service as an irrevocable loss.
4. Armor-piercing projectiles from the BS-3 (100 mm) and A-19 (122 mm) gun completely penetrated when impacting the edges or joints of the "Tiger-B" tank's front hull plates at ranges of 500-600 metres.
5. Armor-piercing projectiles from the BS-3 (100 mm) and A-19 (122 mm) gun completely penetrated the "Tiger-B" tank's front turret plate at ranges of 1000-1500 metres.
Potapov, V. Was the Tiger really King?
To Reiterate, I was trying to articulate, perhaps ineffectively, that velocity > charge/size in terms of the capability to destroy ("knock out") enemy armour. Considering the Is-2 took 3-4 shots to take out a King Tiger, made of an inferior alloy (due to availability) with destructive power coming from shell charge/size.
"In the context of this conversation and given the practical limitations faced during the time period, payload and mass probably were "more important" than velocity."
I strongly disagree, due to the reasons I have illustrated throughout.
Again though, there is no absolute "most important" factor when you remove context.
I agree, context is important, the context being the the capability to destroy ("knock out") enemy armour.
Although in this context, "the IS-2 and Tiger I could knock each other out in normal combat distances below 1,000 m (1,100 yd). At any range, the performance of each tank against each other was dependent on the crew and combat situation"
Zaloga, Steven (1994). IS-2 Heavy Tank 1944-73. Osprey. p. 12.
*Note* I would have included penetration and destruction capability of the D-25 against the superior alloy of the PzV and PzVI although I could fine no non-anecdotal evidence.