Were the 15*69B cartridge a better option for early WWII fighters

Shortround6 said:

When looking at small explosive bullets when does 1-3 grams of HE beat several thousand joules of kinetic energy of impact force?
What is cost of the small explosive bullet vs the cost of a non-explosive bullet in materials, machine time, labor? Times several million or tens of million.

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Hmm, not sure where I was advocating HE shells for such small calibers. I'm not sure those make sense, particularly if you want a fuzed design. There were some designs with fuzeless HE, I guess with more sensitive HE that would explode upon impact. But for HMG class guns, probably something like API makes the most sense.

And we are back to the conflicting basic requirements. With faster aircraft as targets (and faster shooting platforms) you have less time to aim and less time that the target is within the firing area/impact zone. Do you worry about getting hits or the effect of the hits first?
Or with 2000hp engines (and jets are way above 2000hp) do you just stick in number of large, high velocity, fast firing 20mm guns (four 20mm guns at 750rpm each) and go back to research? Nations were still arguing during the 1950s.

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Of course, everything is a compromise and a tradeoff. The ADEN/DEFA guns developed relatively soon after WWII had a MV of about 800 m/s, though generally it seems more modern aircraft guns have tended towards higher MV, something like 1000-1100 m/s seems to be the norm for current day designs. Of course modern jets also have the capability to lug around much heavier equipment compared to WWII planes. Though I wonder about the barrel wear, but maybe with modern guns used so much less maybe barrel wear isn't such a big issue anymore.

z42 said:

Hmm, not sure where I was advocating HE shells for such small calibers. I'm not sure those make sense, particularly if you want a fuzed design. There were some designs with fuzeless HE, I guess with more sensitive HE that would explode upon impact. But for HMG class guns, probably something like API makes the most sense.

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Well, the title of the thread is about using a 15 X 69mm cartridge so?
As usual the thread has drifted but 13-15mm are not that different, cube law says the 15mm is 50% greater than the 13mm. It also says that the 20mm is 2.37 times the 15mm.
Granted for the cube law to be accurate the projectile length has to go up in proportion to the increase in diameter and it often did not.

z42 said:

Of course, everything is a compromise and a tradeoff. The ADEN/DEFA guns developed relatively soon after WWII had a MV of about 800 m/s, though generally it seems more modern aircraft guns have tended towards higher MV, something like 1000-1100 m/s seems to be the norm for current day designs. Of course modern jets also have the capability to lug around much heavier equipment compared to WWII planes. Though I wonder about the barrel wear, but maybe with modern guns used so much less maybe barrel wear isn't such a big issue anymore.

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Post war gun design gets rather complicated. The Early ADEN/DEFA guns were lower velocity than the mid 50s(?) guns, I don't know the change over but there weren't tnat many of the early guns made?
However a lot of the velocity gain of the early guns over the German MK 108 guns was done by using a lighter shell (around 273-296G vs 330G) and using a longer barrel.
Changing the ADEN from an 86mm long case to 113mm long case and using a lighter 247g projectile got the velocity up to 810m/s.

The big modern 30mm guns are so heavy they can't fit more than 2 in the plane. Or they want to use the space for electronics (guided missile support).

Stopping a plane with an atomic bomb made barrel wear kind of disappear, as the cost of many air to air missiles
Different environment, Chrome plating and stellite liners also helped.

Shortround6 said:

There are two advantages to high velocity.
1. More kinetic energy/more destructive power
2. Easier to hit with, especially deflection shooting.

And several disadvantages.
1. As stated earlier 10% increase in velocity needs about 20% more propellent which means
A. more cost in raw materials per round of ammo. Both powder and brass (or steel) to hold it.
B. more weight of ammo per round
C. often a larger and heavier gun, and a lower cycle rate.
D. faster barrel wear.

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Limitations of the platform apply as ever.
A high velocity gun is not such a great idea if it cannot fit on the positions of the aircraft being made, or these just to became mass produced. See the Mk 101 and 103 - good for putting the holes in enemy armor, excellent as AA guns, but next to useless as something one will install on the Bf 109s or Fw 190s and go do air combat. Useless as bomber defense guns.
Germans did have the high velocity gun in the MG 151/15, and they were quick to reduce the MV and increase the target effect when going to the MG 151/20.

Shortround6 said:

When looking at small explosive bullets when does 1-3 grams of HE beat several thousand joules of kinetic energy of impact force?
What is cost of the small explosive bullet vs the cost of a non-explosive bullet in materials, machine time, labor? Times several million or tens of million.

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Since most of the HMG users were willing to have the HE ammo produced for these guns, seems like they considered the benefits outweighing the cost.
Americans, with a lot greater usage of HMGs, were not hard pressed to make each projectile going kaboom.

Several thousands of joules of impact force that is still travelling past the enemy aircraft tail or wing that the bullet just pierced does not seems like the great economy, either.

Shortround6 said:

Or with 2000hp engines (and jets are way above 2000hp) do you just stick in number of large, high velocity, fast firing 20mm guns (four 20mm guns at 750rpm each) and go back to research? Nations were still arguing during the 1950s.

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German focus - this thread being about them - was well past the 20mm guns even before the 2000 HP engines were to be had by them.
They never used the large, high velocity 20mm guns either, bar experimentally.

tomo pauk said:

German focus - this thread being about them - was well past the 20mm guns even before the 2000 HP engines were to be had by them.
They never used the large, high velocity 20mm guns either, bar experimentally.

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In retrospect, a better German WWII fighter armament pathway could have looked something like

1. Start the war with a HMG shooting roughly 750-800 m/s. Use that as the standard bomber defensive gun, and four of them on the Bf 109, as discussed in this thread.
2. Later on, supplement that with a 25mm gun shooting shells with a MV of roughly 750 m/s, instead of the historical MG 151/20 and Mk 108. Due to bigger shells with higher sectional density, would be better than the ping-pong ballistics of the Mg 151/20, and have more punch against bombers. As opposed to the Mk 108, much better muzzle velocity would mean better ballistics and easier to hit fighters with deflection shots.

z42 said:

In retrospect, a better German WWII fighter armament pathway could have looked something like

1. Start the war with a HMG shooting roughly 750-800 m/s. Use that as the standard bomber defensive gun, and four of them on the Bf 109, as discussed in this thread.
2. Later on, supplement that with a 25mm gun shooting shells with a MV of roughly 750 m/s, instead of the historical MG 151/20 and Mk 108. Due to bigger shells with higher sectional density, would be better than the ping-pong ballistics of the Mg 151/20, and have more punch against bombers. As opposed to the Mk 108, much better muzzle velocity would mean better ballistics and easier to hit fighters with deflection shots.

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Very reasonable suggestions.