Alternate armaments for Italian and Japanese fighter

[Nodeo-Franvier]

We know that both the Ho-103 and Breda-Safat was problematic in one way or the others especially with reduced rate of fire when synchronized,What others gun do you think they should be replaced with?
My pick is 11.25mm Madsen m1927 ,13.2mm FN m1939 ,Gebauer m1940 or maybe MG131.

 

[tomo pauk]

We know that both the Ho-103 and Breda-Safat was problematic in one way or the others especially with reduced rate of fire when synchronized,What others gun do you think they should be replaced with?
My pick is 11.25mm Madsen m1927 ,13.2mm FN m1939 ,Gebauer m1940 or maybe MG131.

Can we suggest alternative armament (as suggested in the title), or just alternative HMGs?

 

[Nodeo-Franvier]

Can we suggest alternative armament (as suggested in the title), or just alternative HMGs?

Anything goes.

 

[tomo pauk]

Jump on the Oerlikon FF bandwagon ASAP. Both countries were using engines of under 1200 HP, and in many cases up to 1000 HP, so guns' & ammo weight is a prime concern. Make a deal with Oerlikon for the belt-fed version ASAP, together with the deal for ammo with 100-110g shells so the MV can be 700+ m/s to increase the hit probability. Two per aircraft early on (on G.50, MC 200/202, Re.2000-2002, Ki-43/-44, Zero), later 4 per A/C (G.55, MC.205, Re.2005, Ki-61, etc; also probably on later Zeros and Ki-43s), in the wings outside the prop arc. 4 cannons on 2-engined fighters. Have it sped-up to 600+ rd/min as the war goes on. Adopt the Mine shell design past 1940 (better target effect, 92 g shell should also have a higher MV than the 100-110g one).
On early fighters, add a pair of LMGs or HMGs to complement the two 20mm cannons.

 

[Nodeo-Franvier]

Jump on the Oerlikon FF bandwagon ASAP. Both countries were using engines of under 1200 HP, and in many cases up to 1000 HP, so guns' & ammo weight is a prime concern. Make a deal with Oerlikon for the belt-fed version ASAP, together with the deal for ammo with 100-110g shells so the MV can be 700+ m/s to increase the hit probability. Two per aircraft early on (on G.50, MC 200/202, Re.2000-2002, Ki-43/-44, Zero), later 4 per A/C (G.55, MC.205, Re.2005, Ki-61, etc; also probably on later Zeros and Ki-43s), in the wings outside the prop arc. 4 cannons on 2-engined fighters. Have it sped-up to 600+ rd/min as the war goes on. Adopt the Mine shell design past 1940 (better target effect, 92 g shell should also have a higher MV than the 100-110g one).
On early fighters, add a pair of LMGs or HMGs to complement the two 20mm cannons.

The Zero already got two on the wing though.

 

[tomo pauk]

The Zero already got two on the wing though.

Indeed it had. My suggested change allows predominately for having a much greater on-board ammo supply in 1941-42, thus increasing combat endurance as much is it related to the firing duration. It might make things ... interesting during the air-sea battles of 1942.

 

[tomo pauk]

Heavier weapons: a derivative of the MK 108, but in 25mm calibre. Applicable mostly for Japanese, since by late war the Italians were pretty much out as an independent force. Use the 250g HE shell from the 25mm AA gun, fired at around 700 m/s here.

 

[Nodeo-Franvier]

Heavier weapons: a derivative of the MK 108, but in 25mm calibre. Applicable mostly for Japanese, since by late war the Italians were pretty much out as an independent force. Use the 250g HE shell from the 25mm AA gun, fired at around 700 m/s here.

Even 20mm MG FF/M only managed to 700m/s i don't think 25mm Oerlikon cannon could go that fast.

 

[tomo pauk]

Even 20mm MG FF/M only managed to 700m/s i don't think 25mm Oerlikon cannon could go that fast.

25mm MK 108 derivative should.

 

[Nodeo-Franvier]

25mm MK 108 derivative should.

Mk 108 itself only have muzzle velocity of 540m/s.

 

[tomo pauk]

Mk 108 itself only have muzzle velocity of 540m/s.

MK 108 fired a 330g shell. Japanese 25mm shell was 250g and it was shorter, while the MK 108 ammo protruded well into the casing's cavity thus eating up into propellant charge.

 

[Nodeo-Franvier]

MK 108 fired a 330g shell. Japanese 25mm shell was 250g and it was shorter, while the MK 108 ammo protruded well into the casing's cavity thus eating up into propellant charge.

The only Japanese 25mm round i know of is from the anti aircraft gun.

 

[tomo pauk]

The only Japanese 25mm round i know of is from the anti aircraft gun.

Bingo.

 

[Dimlee]

Later in the war, Mk108 and Mk103 against bombers?

 

[tomo pauk]

Very powerful guns - especially the 103 - but both of the two strike me as extremes. The MK 103 was ill suited for the typical Japanese 1-engined fighter of the day since it took two of them to be installed outside the wing (bad for streamlining), while the recoil was judged as too violent even on the sturdy Fw 190s. The 108 was far easier to install, while providing extra 50% of RoF, but muzzle velocity was very low thus lowering hit probbility, especially if a low-hours pilot is in the cockpit. Germans stated that a single MK 108 have had just 50% of chance to hit when compared with a single MK 103. MK 108 and 103 used the same 'Mine' and incendiary type shells - probably a bit too light for MK 103, and in the same time certainly too heavy for Mk 108. MK 103 used a greater variety of ammo, including the HE shell that weighted 440g.
A reason for my suggestion to have a derivative of MK 108 firing the lighter 25mm shell that Japanese are already producing - 250 vs. 330 g - coupled with a slightly increased propellant charge is to cure the main MK 108's problem, bringing the MV in the 'useful' range. Granted, a MK 108 firing a new 30mm Mine shell that weights 250-270g is another way of increasing the MV.
For the MK 103, I'd suggest a ~400g mine shell; a 2-3-4 gun battery would've done just fine aboard the 2-engined A/C, jets, and/or pusher A/C.

 

[Shortround6]

I think your ballistics are a bit off.

The 25 x 163 is the Hotchkiss round used by the Japanese. It is 42.7mm in diameter just in front of the extractor grove. The German 30mm MK 108 case was 32.3mm in diameter just in front of the grove. The Hotchkiss had 101,000 joules of energy for the 250 gram HE projectile, the MK 108 had 42,100 joules.
Your proposed round would have a muzzle energy of over 61,000 joules. (250 grams at 700m/s) even if the velocity was 600m/s you would have just under 45,000 joules.

Interior ballistics problem with that is that you have less area on the base of the projectile to push against. And your projectile has more sectional density. perhaps not a lot but you need more chamber pressure to get the results you want or even get 600 m/s.

 

[tomo pauk]

I think your ballistics are a bit off.

The 25 x 163 is the Hotchkiss round used by the Japanese. It is 42.7mm in diameter just in front of the extractor grove. The German 30mm MK 108 case was 32.3mm in diameter just in front of the grove. The Hotchkiss had 101,000 joules of energy for the 250 gram HE projectile, the MK 108 had 42,100 joules.
Your proposed round would have a muzzle energy of over 61,000 joules. (250 grams at 700m/s) even if the velocity was 600m/s you would have just under 45,000 joules.

Interior ballistics problem with that is that you have less area on the base of the projectile to push against. And your projectile has more sectional density. perhaps not a lot but you need more chamber pressure to get the results you want or even get 600 m/s.

Indeed, with just 30g of propellant my 'MK 108/25' will not do 700 m/s with 250g shell. Soviet 'short' 23mm was doing 610 m/s for 200 g shell on 33g of propellant (or 175g shell at 690 m/s). The increase of propellant weight to close to 40g is needed if the weapon can withstand it. A longer barrel, too, to take advantage of greater propellant weight.
Muzzle energy does not tell the whole story. MG 151/15 have had up to twice the muzzle energy than MG 151/20 despite just ~1/3 more propellant. Since the m.e. goes up with with square of speed vs. going up proportionally with mass, it will 'favor' the guns that fire lighter projectile/shell.

Another way the Japanese might get the bigger cannon without wasting too much time is that they get the captured Soviet VJa-23 from the Germans, and neck-up it to 25mm, thus using Japanese barrel making equipment and shells for series production. Ammo for VJa-23 have had propellant weight of 64.2g, making the 183-190g shells/projectiles go 980-970 m/s.

 

[Admiral Beez]

What the Japanese need is more, not so much different guns. 1941, Ki-43 Oscar has the same armament of a Sopwith Camel, twin .303 machine guns, that's it. Meanwhile 1939 Spitfire and Hurricane have eight.

 

[Shortround6]

Ki-43 Oscar has the same armament of a Sopwith Camel, twin .303 machine guns, that's it. Meanwhile 1939 Spitfire and Hurricane have eight.

Sopwith Camel had Vickers guns that fired at about 600rpm each before synchronization.
Ki-43 Oscar had Vickers guns that fired at about 900rpm each before synchronization. 50% increase in firepower?
Spit and Hurri used Browning's that fired at 1200rpm each and were not slowed down by synchronization. Over eight times the firepower of the Camel. Over 5 times the firepower of the Ki-43.
A Ki-43 with one 12.7 and one 7.7 was better but still only about 1/4 the firepower of the eight gun British planes.

 

[Admiral Beez]

Sopwith Camel had Vickers guns that fired at about 600rpm each before synchronization.
Ki-43 Oscar had Vickers guns that fired at about 900rpm each before synchronization. 50% increase in firepower?

Bravo for Japan on the ROF increase I suppose. My point though is twin Vickers in 1941? That's the best you can do?