US ww2 issue 20mm HE VS: 55gal. empty oil drum

[GRUNHERZ]

How come the ammo feeds in all the way in the back?

[GScholz]

Originally posted by Wotan
The berezin had a rof of 800rpm same as the shvak. The mg151 700-750rpm.

Rof is not the same as muzzle velocity.

[Crumpp]

Rof is not the same as muzzle velocity.

Absolutely right. ROF is not constant either.  Heat, dirt, and condition of the springs/weapon, all work to vary the ROF.  Some weapons vary more than others within the same design.
All are designed to fire within certain parameters.  For example the M60 Machinegun had a cyclic rate of 550 rpm.  Cyclic rate is simply a theoretical rate of fire assuming:

1.  Unlimited supply of ammunition

2.  Weapon never over heats or malfunctions

The practical rate of fire for the M60 is on the order of 100 rpm with a barrel change every 10 minutes.  This is the "sustained" ROF and the weapon was designed to fire all day at this rate.

For emergency purposes you could fire 200 rpm with a barrel change every 2 minutes for no longer than 10 minutes.

Depending on the design, the practical rate of fire maybe very similar to a weapon with a much higher or lower Cyclic ROF.

Crumpp

[Edbert1]

Originally posted by Crumpp

I think this springs from the fact that the MGFF in AH is a very very weak cannon when it should not be at all.  The MG151's seem kind of weak as well.  

My problem with the German 20mm is the trajectory, they seem to be about 75% the velocity of the Hispano, either that or the projectile itself suffers ballistically. If the bullet hits, I see little difference in the lethality/damage inflicted by the Hispano and the MG151/20, the FF is a little weaker IMHO. This is from years of playing and is entirely subjective, I have no hard data.

[Karnak]

Tony,

Firing a MG151/20 HE or MINE shell with the gun synchronized for 300 meters and a Hispano Mk II HEI synchronized for 300 meters, how different would would the positions of the shells be at if they impacted a target at 150m, 450m, 600m and 750m?

[GScholz]

The Hispano II HE shell only has a 7.5% higher muzzle velocity than the MG151/20 HE(M) shell, and 22.8% higher than the MG-FF/M HE(M) shell.

Hispano II HE: 860 m/sec
MG151/20 HE(M): 800 m/sec
MG-FF/M HE(M): 700 m/sec

For comparison:
M2 .50 BMG: 890 m/sec
Browning .303: 762 m/sec
MK108 30mm HE(M): 505 m/sec

[Edbert1]

Originally posted by GScholz
The Hispano II HE shell only has a 7.5% higher muzzle velocity than the MG151/20 HE(M) shell, and 22.8% higher than the MG-FF/M HE(M) shell.

Just to clarify, I was talking about my experience in the game. I can hit relaibly with hispanos out to 700-900 meters, but have trouble adjusting to the drop in the 151 equiped rides. I can't think of how many kills I've lost at 300-400 meters seeing the shells fall underneath my target. In AH they just seem to drop, the Japanese ones do too, but not the Russian ones. Not that I am a LW conspiracy type or anything.

I found this thready to be very interesting.

[Tony Williams]

Originally posted by Karnak
Tony,

Firing a MG151/20 HE or MINE shell with the gun synchronized for 300 meters and a Hispano Mk II HEI synchronized for 300 meters, how different would would the positions of the shells be at if they impacted a target at 150m, 450m, 600m and 750m?

I don't have a trajectory diagram for the Hispano. However, the result would be affected by the postion of the sight relative to the guns. Other things being equal, the greater the vertical distance between the guns and the sights, the flatter the gun will appear to shoot.

Tony Williams: Military gun and ammunition website and discussion
forum

[Tony Williams]

Originally posted by GScholz
The Hispano II HE shell only has a 7.5% higher muzzle velocity than the MG151/20 HE(M) shell, and 22.8% higher than the MG-FF/M HE(M) shell.

Hispano II HE: 860 m/sec
MG151/20 HE(M): 800 m/sec
MG-FF/M HE(M): 700 m/sec

But you need to remember that the Hispano's shell weighed 130g, the M-Geschoss only 92g - and even the 'heavy' conventional German 20mm shell only 115-117g. And the lighter the shell, the faster it loses velocity and the more quickly the trajectory drops (other things being equal, as usual!).

Tony Williams: Military gun and ammunition website and discussion
forum

[GScholz]

Yes of course, but at normal firing distance, i.e. a convergence range of 200-400 meters the difference in projectile weight would have little effect. At greater ranges the difference would be more of a factor.

[Karnak]

GScholz,

I don't think you'd see much difference at 200 or 300 meters.  By 400 meters I think noticable differences will be creeping in.  By 850 meters, the longest range kill I am aware of in WWII, there would be very clear differences.


But more noticable than the drop would be the time to target.  The higher muzzle velocity of the Hispano shortens the time it takes to get to the target and therefor makes mild deflection shots a bit easier.  I would be very surprised if high deflection shots were any easier or harder with either gun.

[Wolfala]

I'm amazed that after 60 years the powder didnt go bad

[HoHun]

Hi everyone,

Nice thread :-)

I'd say we all more or less agree on the qualitative effects.

What's difficult is reaching a reliable conclusion because it's difficult to say which effect outweighs which other effect.

I've tried to combine several factors into the sight pictures I originally posted in the parallel gunnery thread.

It might be that the MK108 dispersion as displayed below is only 50% of what it should be, I haven't yet figured that out.

So, the diagrams are more a demonstration of what we should look at before drawing conclusions.

For example, for judging the value of a flat trajectory, we should check out where the aiming point has to be for each weapon for a good hit probability at different ranges.

The surprising thing is, with the low-velocity blunt-nose low-sectional density MK108, you can just put the crosshair dead on target centre out to 500 m and expect good hits within half a fuselage diameter.

With the high-velocity, flat trajetory, wing mounted M2, there's no drop to speak of (though you have to watch out for the "rise" at 100 m! :-), but still at 500 m, aiming is tough because of the diverging bullet streams. To place the bullet stream on target, at 500 m you've to aim farther out to the side with the M2 than the bullet drops for the MK108!

(That's, as you're all aware, only for a stern attack at a target flying straight and level. But I think it's a good start for a weapons system-oriented discussion. We can add complexity later :-)

The conclusion I'd like to suggest: The benefits of a centre-line mount far outweigh the benefits of a flatter trajectory in such a situation.

If that's confirmed by an M2 vs. MK108 comparison, it will be even more obvious in a Hispano vs. MG151/20 comparison.

Regards,

Henning (HoHun)

P-47 battery:

http://www.x-plane.org/users/hohun/p47guns.gif

Nose-mounted MK108:

http://www.x-plane.org/users/hohun/nose_mk108.gif