You guys are gonna love this....although I hasten to add I found it at Netwings
"A. S. Nikolay Gerasimovich, if you compare the Hispano-Suiza 20mm cannon and the ShVAK, which was better in your opinion?
N. G. Ours, without a doubt. The ShVAK was twice as reliable. The Hispano simply required an unbelievable amount of maintenance. The smallest exposure to dust, congealed lubricant, or any other kind of little thing, and the gun would not fire. Very unreliable.
The ballistics of our cannon were better. Our cannon had a flatter trajectory, which is significant for applying lead. When you talk about the Yaks, then one didn’t even need a sight. The tracers were almost straight, take aim and fire, and where the nose is pointing is where the rounds struck.
Our ShVAK had a higher rate of fire.
Regarding the target effect, these two cannons were about equal. In either case, there was no difference that I could see with the human eye.
and
A. S. Was a 37mm cannon necessary? Wasn’t this too large a caliber for a fighter? You had so few rounds of ammunition. And wasn’t its rate of fire slow?
N. G. One cannot say that the 37mm cannon was a disadvantage or an advantage. Look at it from this perspective. The M-6 cannon had its strong and weak points. One had to take advantage of the strong points and compensate, as much as possible, for its weaknesses.
These were the weaknesses: 1. Low rate of fire. 8 rounds/second [this is incorrect—the correct rate is slightly over 2 rounds/second (130 rounds/minute) – J.G.] This is indeed a low rate of fire.
2. The ballistics of the projectile were abysmal. The flight trajectory of the projectile was arching, which required large lead angles. But again this was at long ranges, especially when firing at ground targets. When firing at ground targets we had to apply two rings of the sight for lead.
3. Minimal ammunition supply. Thirty rounds.
All these deficiencies could be compensated for by proper selection of firing range. If one fired from 70—50 meters, there was sufficient rate of fire, the ballistics at this range were acceptable, and the lead required was minimal. Thus, all the weaknesses of the 37mm cannon listed above revealed themselves only at long ranges.
Now regarding the strengths: 1. The projectile was very powerful. Normally, one strike on an enemy fighter and he was finished! In addition, we fired this cannon at other types of targets. Bombers, vessels at sea. The 37mm cannon was very effective against these targets.
Here is an example. Our patrol torpedo boats had torn apart a German convoy. The majority of them had in some way or other been damaged, but they were withdrawing. One patrol boat was heavily damaged and lagging behind a bit. German “hunter” boats were closing in on it. One of them moved in either to kill or capture it. There were eight of us; my squadron commander Vitya Maksimovich, had flown out in pair slightly ahead of us to reconnoiter the convoy and I was leading the other six. We were listening to the conversations of the PT boat crews (the PT boats, by the way, were American Higgins craft). The commander of the heavily damaged boat said, “They are on top of us!” My squadron commander said to him, “Don’t worry! I ‘ll get him now!” He dropped down and fired a burst of 37mm cannon. It was a pleasure to watch the German “hunter” go up in flames. Six Bf-109Fs were covering the convoy and supporting the attack on our PT boats. I engaged them with my group of six Cobras. We circled round and round. I shot down two Messerschmitts and damaged one (intelligence subsequently confirmed the damaged 109). Before we had even landed, the crew of the damaged PT boat reported by radio that one of the Cobras had shot down two Messers and another had set the German “hunter” on fire. This had all happened right in front of their eyes. Later Admiral A. V. Kuzmin, commander of the patrol torpedo boat brigade, personally expressed his appreciation to us. All our damaged PT boats made it back to their base.
Thus, a single burst of several 37mm projectiles was sufficient to set fire to or damage a “hunter-type” patrol vessel.
Its all here ITS ALL HERE