Thats what I wanted to know... how does it affect the impact.
I asked, because length of rounds is very imp. in artillery rounds, so.... was wondering if they make a big difference in Tank munitions.
Generally long rod penetrators perform better than shorter ones. If you compare the rounds of the same generation US/NATO v Soviet 1970-1986 before the Soviets abandoned the bore riding saboted deigned in favor of the spool style sabots you see a huge differance. The 105mm M744 had a penetration of 345mm vs the Soviet 3VBM9/3BM22/23 which did 380mm,
345/105= 3.29mm of penetration per mm of round diameter
280/125= 3.04mm of penetration per mm of round diameter
The newest Russian round the 3BM46 has a penetration <600mm and a length of at least 560mm. The US M829A3 has a penetration <800mm and a length of 835mm. So it follows that a longer and heavier penetrator will perform better.
A scary thought is if the US converts to the 120mm L/55 and the M829A3 can handle the higher velocities- the energy delivered from that round going around 1700m/s is huge. Currently figuring a 1.5kg sabot weight the 8.5kg round will deliver around 10.8mj. Boosting the velocity to 1700m/s boosts the energy to 13mj. Compare this to the estimated 2.4kg weight of the 3BM46 at 1700 which delivers about 6.6mj The 3BM46 is the best round India could have for the T-90 as it is state of the art Russian. The Indian T-90's gun is outperformed by the current US Abrams gun combo round by at least 50%