Why are the cannons so weak on the 109-E, yet so strong on the Russian planes?

[Panzergranate]

The power of a gun is determined by the length of the barrel in relatition to its bore. This is given as a figure refered to as the Calibre Length, which is given as an "L" number, in cannon ballistics.

For example, a gun described as being 20mm. L55 is 20mm. bore by 20 x 55 millimetres in length.

The bigger the L number the more high velocity the shots fired.

The 0.'50" (12.7mm.) HMGs on the P-51 B are higher velocity than the short barrelled versions on the P-51 D because of the higner velcoity.

Back to the diffences in hitting power between the German and Russian 20mm. cannons..... it is down to gun velocity and ammunition differences.

The German 20mm. cannon is L30 in length/

The Russian 20mm, cannon is L107 in length.

The German 20mm. Solothurn HE cannon shell contains a blue coloured semi-explosive incendary content and isn't particularily large. The AP round, like all AP rounds, is a non-explosive solid manganese steel slug that will punch through steel and thin armour plate found on some aircraft.

The Russian ShVAK fires a much larger shell , with a much larger propelling cartridge down a longer barrel at a higher velocity. The shell is APHE (Armour Piercing High Explosive) designed to penetrate tank armour. It could penetrate around 50mm. of steel and 27mm. of armour plate.

The same goes for the British 20mm. Hispano cannons, long barrelled and high velocity. The Hispano will punch through over 75mm. of steel and 42mm. of armour plate.

The German cannons are underpowered because they actually were in real life.