To be clear, I was only responding to the assertion that the M.S.406 was underarmed. The accusation certainly doesn't make sense in comparison to the D.520, which only added two more MAC-34s.
We can also recall that MG FFM was used aboard Fw 190s by some two years.
For space reasons, not because it was a desirable weapon. Mixing the ballistics of three weapons was really, really sub-optimal.
In any case, a side issue, and you're definitely right that having a cannon was better than not.
The MG 151 cannon in the 109's propeller, after they finally (after several years) got the MG/FF to work in that position with an acceptable level of reliability, had several advantages over the MG/FF.
1. much greater ammo capacity.
2. higher rate of fire, around 700rom vs 500rpm (at best?)
3, higher velocity making deflection shooting easier. (the MG 151/15 was the champ but the MG 151/20 fired shells (non mine) 18% faster than the MG/FF with a corresponding reduction in flight time).
Yep, yep, yep, and yep. No arguments there, even if it doesn't directly relate to the question of the Bf109E-3 and early -4's armament compared to the M.S.406.
I suspect that getting rid of the wing guns improved roll rate, along with other things. And dang, the increase in ammo capacity made up for everything.
As far as the Ms 406 argument goes. 60 rounds is 60 rounds. you have 60 rounds of 20mm ammo. the 109E-3 had 110-120 rounds depending on how full the drums were even if they weren't mine shells.
1 or 1.5 seconds extra firing time for the slower firing cannon isn't that big a deal. How many pilots succeeded using their last 1-2 seconds of ammo? Not saying that a few didn't get a kill that way but it wasn't a huge factor.
Particularly the fire before that last burst is less effective than the competition. That said, at least if you can sight in with the MGs, you can get a lot more out of that last burst than you otherwise would.
From Lundstrom's The First Team, the Wildcat pilots seem to have done a lot of damage with their final bursts, often because they were finishing off damaged aircraft or were firing from shorter range than before. There were probably other factors. OTOH, if you can just hit and kill the target with your second burst, you're better off all around.
Incidentally, I see that the D.520 had switches that were apparently selectors for the cannon and each wing's machine guns. (The could be for charging, I suppose.) Anyone know if this is correct? Did the M.S.406 have selectors?