USAAF 0.60-caliber Machine Gun????

[Avimimus]

That's right. It's not a very interesting consideration in air combat though as aircraft are fairly soft targets. The US ballistics tests I quoted above show the percentage of vulnerable area of the target aircraft in the test to the different weapons, and explosive shell capable of damaging the aircraft structure have a clear advantage here, so I'd say optimizing for penetration would not be a good strategy.

Thanks for the detailed reply.

A couple of additional observations:

- Passing through aircraft skin induces yaw in bullets, which tends to reduce penetration by two or three millimetres. When one considers armoured seats, components, and fuel tanks may protect key components (pilot, engines) when fired on from the rear, and the strength of structural elements like spars... differences in penetration can actually have a significant effect. Of course this is most significant for the smallest calibre weapons (but does make them less effective overall compared to heavier weapons).

- Filling weight (for incendiary or explosive mixtures) differs significantly within the heavy machinegun range. So the difference between an Browning's M1 and an M23 means that the post-war round will have significantly better terminal effects. The same goes for the UB/UBS/UBT and MG-131 - both of which benefitted from considerably larger fillings. I think this impacts these medium calibre weapons the most (as they are the ones which have round volumes which are just beginning to carry meaningful bursting charges, but also vary the most in the ratio of steel to filling - as any amount of filling is relatively marginal and slight thicker walls can render the filling trivial).

So there is an argument for slightly reducing the firepower of rifle calibre weapons, and incorporating more variation in the firepower of heavy machine guns.

I suppose one would do the latter (adjust for filling weight) through using a non-linear equation that treats variation in filling as being relatively significant on the low end, but the differences being less significant in the high end (perhaps ignoring the effects of shrapnel and apply a square/cube function to treat the rounds as purely blast/volume based)?

You're right again It's fairly complicated though, as the influence depends on further factors such as (already pointed out by you) the velocity of the shooting platform as well as of the targeted platform, as well as the flight altitude. I ran the numbers for a selection of weapons for which I had the data, and it turned out that the higher-velocity, machine-gun type weapons mostly relying on kinetic energy for effect lost power downrange quicker than the lower-velocity cannon, as the chemical energy of the shell contents remained unaffected.

So, it's sort of conservative to use muzzle energy in as far as not to underestimate the smaller calibres.

Regards,

Henning (HoHun)

This might be a reason why the transition to lower velocity higher volume rounds was common in the post-WWII era (e.g. NS-23/NR-23, N-37 are both favouring lower velocity but heavier rounds). Similarly, the abandonment of the 0.60.

There is also the probabilistic factor - how conservative are pilots in pulling the trigger, how long a burst can they fire, what area is covered by that burst. Looking at the Bf-110 in its primary characteristics (airspeed, firepower per second, turn time) it should have been competitive - it is only when one considers that it was a larger target (with a lower roll rate perhaps) that we see why it failed. So, I think the full picture involves the probability of hitting a target multiple times with an average skill pilot in a typical combat situation - and that might give a bit of an edge back to heavy machine guns or lighter cannons (higher combined rate of fire, higher muzzle velocity). That is very difficult to include in a calculation though! Will reply to the Col. Coats discussion later.

 

[HoHun]

Hi,

- Filling weight (for incendiary or explosive mixtures) differs significantly within the heavy machinegun range.

I have tried to account for these differences by calculating the average for representative projectiles and belting orders.

I suppose one would do the latter (adjust for filling weight) through using a non-linear equation that treats variation in filling as being relatively significant on the low end, but the differences being less significant in the high end (perhaps ignoring the effects of shrapnel and apply a square/cube function to treat the rounds as purely blast/volume based)?

It would be possible to calculate such a figure of merit, but its applicability would be more limited, and perhaps more controversial. It might be more accurate if well-matched to a specific scenario, though.

There is also the probabilistic factor - how conservative are pilots in pulling the trigger, how long a burst can they fire, what area is covered by that burst.

Very good point - pilots will probably open fire when they think they have a certain probability of actually achieving a victory, choosing how much ammunition they consider expendable based on their supply, and balancing it with their perception of weapon effectiveness.

Regards,

Henning (HoHun)

 

[HoHun]

Hi,

As I pointed out earlier, the 16 mm Vega appears to be kind of a missed opportunity. You're basically a barrel change away from converting your machine guns into cannons while retaining your original ammo loadout...

Do you happen to have any numbers for the 16 mm Vega (gun weight, rate of fire, muzzle velocity, projectile weight, filler weight etc)? Seems they these are hard to find, maybe because the cartridge is so esoteric.

I ran some back-of-the-envelope calculations for 17 kJ muzzle energy with increasing projectile weights, and unless the filler percentage is increased along with the weight, total muzzle energy in relation to loaded battery weight doesn't improve much with heavier projectiles, and there certainly seems to be no big leap possible.

Also, I have been relying on Tony Williams' number of 890 m/s as muzzle velocity for the AN/M2 API projectile as a baseline, and somehow I am confused now if this is really the correct number for the aircraft version ...

Regards,

Henning (HoHun)

 

[MihoshiK]

Hi,



Do you happen to have any numbers for the 16 mm Vega (gun weight, rate of fire, muzzle velocity, projectile weight, filler weight etc)? Seems they these are hard to find, maybe because the cartridge is so esoteric.

I ran some back-of-the-envelope calculations for 17 kJ muzzle energy with increasing projectile weights, and unless the filler percentage is increased along with the weight, total muzzle energy in relation to loaded battery weight doesn't improve much with heavier projectiles, and there certainly seems to be no big leap possible.

Also, I have been relying on Tony Williams' number of 890 m/s as muzzle velocity for the AN/M2 API projectile as a baseline, and somehow I am confused now if this is really the correct number for the aircraft version ...

Regards,

Henning (HoHun)

It's not that you'd get more muzzle energy, it's that the 16 mm Vega would have gotten the USAF an actual cannon round, which would actually do BOOM on contact at all altitudes, and which would carry more explosive filler than a .50 round.

 

[Colonial-Marine]

I think a battery of guns firing 16mm Vega would have been quite effective by WWII standards, but against early 1950s jets and beyond I think it would also become somewhat inadequate much like the assessment of .50 caliber guns in the air war over Korea.

 

[MihoshiK]

I think a battery of guns firing 16mm Vega would have been quite effective by WWII standards, but against early 1950s jets and beyond I think it would also become somewhat inadequate much like the assessment of .50 caliber guns in the air war over Korea.

One of the biggest problems with the .50 in Korea was that the rounds relied on the filler igniting on contact, and at high altitude that apparently was iffy. The Vega would have remedied that. I mean, compared to even 20 mm rounds it would have been kinda anemic, but the US had big problems adopting the early 20 mm cannons.

 

[HoHun]

Hi,

It's not that you'd get more muzzle energy, it's that the 16 mm Vega would have gotten the USAF an actual cannon round, which would actually do BOOM on contact at all altitudes, and which would carry more explosive filler than a .50 round.

I think we're mostly in agreement, but there might be a slight misunderstanding: I wasn't considering kinetic energy alone, but total (kinetic plus chemical) energy, which includes the explosive (or incendiary) filler.

The 12.7 mm API according to Tony Williams has 43g weight with 2% chemical content, while the German 15 mm High Explosive shell has a 57 mm weight with 4.9% filler. Assuming the 16 mm Vega had the same parameters as the latter, and 17 kJ kinetic energy, the projectile would have a muzzle velocity of 770 m/s and a total muzzle energy of 33 kJ, about 150% of the 12.7 mm API round.

The question might be, would it be possible to create a 12.7 mm round with the same 4.9% filler percentage? That would come out at 29 kJ at the original muzzle velocity, without requiring a calibre change. I presume there's a minimum practical size for fuses, and they'd tend to make up a greater percentage of the projectile weight the smaller the projectile is, so instead of 4.9%, one probably would end up with a somewhat lower number.

For comparison, the 0.60-caliber round of the T17E3 might come out at something like 46 kJ kinetic energy, 21 kJ chemical energy, 67 kJ total energy, or about 200% that of the 16 mm Vega, or 300% of the 12.7 mm API round.

All based on fallible guesstimates of incomplete and probably mismatched data, but it might at least show the general difference between the two approaches

Regards,

Henning (HoHun)