50 cal (high rate of fire) vs 20mm cannon (hitting power)

[A.G. Williams]

Hispano's were a hybrid gun. They used a combination of gas and recoil. The shorter lighter barrel helped with the increase in the rate of fire.

It was a hybrid but with a combination of gas and blowback. Gas tapped from the barrel was used to unlock the breech, after which gas pressure in the barrel blew the fired case backwards and out of the gun.

The rate of fire was determined by a number of factors, barrel length wasn't that significant.

 

[jmcalli2]

"Under 5 mph speed loss on average for the cannon-armed Typhoon is hardly significant."

5mph is not significant unless the 392-393mph Typhoon IB comes into contact with the 408-410mph Fw 190A5 at 20,000ft. Fortunately for the RAF the Sabre engine's power improved.
Speed loss occurs in trifles: gun ports, wheel well covers., retractable tail wheels, gaps in the radiator etc.

The barrel length of the Hispano II became more of an issue on the Tempest (due to its slimmer wings and higher targeted speed) and the Spitfire F22/F24 series which both needed the short barrelled Hispano V.

The gun was troublesome in wing installations. The US version which used a slightly different cartridge never became reliable enough to put into service despite millions of rounds of ammunition being produced.




"

You also need a heavier structure to support the heavier recoil. In the P-39/63 the huge 37mm was supported by the center of the aircraft; the plane was designed around it. The German Mk 101-103 with their high muzzle velocity posed the structure problem; one of the reasons for the Mk 108.

 

[jmcalli2]

ok what does mg 151/20 stands for then?

View attachment 601430

The original gun was the Mg 15 for 15mm. The design was modified with a new chamber and barrel and became the 20mm Mg 15/20.

 

[jmcalli2]

View attachment 601455

Yes the Hispano's were big.
Hispano's were a hybrid gun. They used a combination of gas and recoil. The shorter lighter barrel helped with the increase in the rate of fire.

Hispanos were anything but short: it was 93 aches long. The MgFF was 53 inches long, the M4 Browning 37mm was 89 inches long, and the Browning .50 cal was 65 inches long.

 

[tomo pauk]

The original gun was the Mg 15 for 15mm. The design was modified with a new chamber and barrel and became the 20mm Mg 15/20.

MG 15 was s LMG, for 7.92mm ammo.
MG 151/15 was a cannon for 15mm ammo. MG 151/20 was the 20mm version.

 

[Admiral Beez]

The 20mm Hispano and Browning M2 had similar rates of fire, and similar muzzle velocities.

Yes, speed and frequency to target may be similar, but unlike the solid lead of the .50 cal, the 20mm explodes on impact.

 

[jmcalli2]

MG 15 was s LMG, for 7.92mm ammo.
MG 151/15 was a cannon for 15mm ammo. MG 151/20 was the 20mm version.

Thanks for correcting me!

I blame a coffee deficiency.

 

[A.G. Williams]

Yes, speed and frequency to target may be similar, but unlike the solid lead of the .50 cal, the 20mm explodes on impact.

A bit of nit-picking: the standard .50 cal ball didn't have a lead core, it had a steel one in a thin lead sleeve. From 1944 onwards, the favoured bullet type for fighter aircraft was the M8 API; this had a hardened steel armour-piercing core with a quantity of incendiary material in the jacket tip. It was common to make every fourth or fifth round an M20 API-T (tracer). For bomber defence, the .50 often used the M21 "Headlight" tracer; it had been discovered that attacking Luftwaffe pilots could be distracted by seeing the tracers coming towards them, so the M21 was designed to have a big, bright tracer which could easily be seen from the front.

The standard RAF 20mm Hispano belt make-up from mid-war onwards was two HEI followed by two SAPI (semi-armour-piercing-incendiary). The HEI had a fuze with a slight delay, to ensure that it exploded inside the target rather than on the surface. The SAPI shells used the same shell body as the HEI, but were filled with a large quantity of incendiary material and were given a penetrating steel cap instead of a fuze; the incendiary was ignited by the shock of impact. They both worked pretty well, once the early problems with over-sensitive fuzes were dealt with (the Luftwaffe had the same problem with their 20mm HE).

 

[tomo pauk]

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Tony, since you're here - is there a manual for the Hispano V available for easy download?

 

[Greyman]

Supermarine and Hawker fitted the Hispano V on their fighter because the Hispano V was now available, and Hispano II was being phased out production. It offered 750 rd/min* vs. 600 rd/min for the Mk.II - so basically it was a firepower of 5 Mk.IIs for weight penalty of 3.5 Mk.IIs.

150 rounds/min faster, 30 lb lighter, and greater simplicity of installation were the main 'selling' points. The loss of 65 ft/sec in muzzle velocity was a small price to pay for these improvements -- especially with gyro sights.

 

[tomo pauk]

150 rounds/min faster, 30 lb lighter, and greater simplicity of installation were the main 'selling' points. The loss of 65 ft/sec in muzzle velocity was a small price to pay for these improvements -- especially with gyro sights.

Agreed. A combination of heavy shell, very good RoF, still very good MV and reasonable weight were strong selling points of the Hisso V.
Seems like the weight difference for a single gun was 8 kg - around 20 lb.

 

[Admiral Beez]

Were all WW2 aircraft cannons metric?

 

[Greyman]

A couple of the heavier British cannon (Vickers 'S', Mollins 'M') are sometimes referred to as 2pdr and 6pdr respectively -- but I think the official designations stuck with metric.

 

[Shortround6]

It was a hybrid but with a combination of gas and blowback. Gas tapped from the barrel was used to unlock the breech, after which gas pressure in the barrel blew the fired case backwards and out of the gun.

The rate of fire was determined by a number of factors, barrel length wasn't that significant.

Thank you for the correction.

I think I was confused by the recoil absorbing mountings. The entire gun recoils with each shot and is returned to the forward position before the next one but the guns movement doesn't do anything to operate the action. Except that the belt feed guns use the movement of the gun to power the belt feed mechanism.
The Spring mounts do lessen the recoil impacts on the airframe.

Lighter reciprocating parts (or entire gun) would help the rate of fire?

 

[Koopernic]

T

Supermarine and Hawker fitted the Hispano V on their fighter because the Hispano V was now available, and Hispano II was being phased out production. It offered 750 rd/min* vs. 600 rd/min for the Mk.II - so basically it was a firepower of 5 Mk.IIs for weight penalty of 3.5 Mk.IIs.

Problem with, typically, Spitfire V lugging around 4 cannons was lack of engine power for such a heavy battery. Similar problem was shared by many P-40s, P-39s and Fw 190As.



The no free lunch rule applies as ever - 5 mph speed loss was diminutive price to pay for huge increase of firepower. The Fw 190A lost same amount of speed when it swapped the fuselage LMGs with HMGs, for a very small % of increase of total firepower. Some aircraft required gondolas when wanting to go from 1 cannon to 2 or 3, with a major performance loss.



Armour penetration & kinetic energy was not high on the RAF's list. Increase of rate of fire, while saving close to 80 lbs per 4-barreled installation, was high on the priority list. Muzzle velocity of 840 m/s was still higher than what German, Soviet or Japanese 20mm cannons offered.



(my bold)
Don't post misinformation.



Source for MG 151 having a non-locking bolt? What kept the installed weight down for MG 151 was that it was not firing a really powerful cartridge vs. what Hispano used.

*in a lot of places the 800 rd/min is quoted for Hisso V

The UK deployed 3 versions of their implementation of the Hispano: the Mk I (on the Hurricane) and Mk II (On Typhoon, Spitfire and early Tempest) and Mk V which was the short barrel version of the gun on the Tempest and Spitfire F22 and F24.

Your claim is that shortening the barrel was done for reasons of increasing rate of fire rather than aerodynamics. Apart from contradicting a expert in this thread there are two arguments against this:
1 The Full length US Hispano, All 2.45m of it, known as the M1 achieved a cadence of 700rpm which is 100rpm greater than the full length British versions of the same time. I'm not even sure what the ROF of the Hispano 2 was, it seems to have increased. It may have been greater than 600. The latter US M2/M3 versions were shortened like the Hispano V.

2 Unlike the Oerlikon the Hispano fired from a locked breech bolt. When the round being fired eventually passed a gas port which channelled gas back to a piston that was used to unlock unlocked the bolt. Residual gas pressure then ejected the spent cartridge casing against the bolt.

By contrast the Oerlikon's API mechanism fired while the bolt was moving forward, the mass of the bolt had to be high to slow the bolt enough and arrest the the recoil and this created a trade of between cadence, muzzle velocity and weight.

The Mauser MG151 used a short recoil. The bolt was locked with the barrel like the Hispano, however after firing the motion of the barrel unlocked the bolt after a short recoil (instead of gas). The barrel then stops quickly but the bolt continues backward (via inertia and residual pressure) to allow extraction and reloading. This mechanism has less of a trade of but it also has the advantage of firing from a closed bolt that helps synchronisation.

The Hispano mechanism should have been suitable for synchronisation.

The Hispano was thus not dependant on the a heavy bolt, as in Oerlikon and Mk 108 because the locking mechanism meant the round left the barrel before the lightweighed bolt opened since it remained locked till the gas port was exposed.

The Gas channels in the Hispano represent an area that needs cleaning because it is vulnerable to fouling as well as being a complication.

The long barrelled Mauser Mk 103 used a gas mechanism to unlock the bolt but used barrel recoil for extraction.
The German 3.7cm FLAK 18,36 & 37 used it as did the highly refined 3.7cm FLAK 43.

Incidentally the full length HS 820 (2.45m) fires at 1000 rpm using a gas mechanism. (not revolver)

 

[Greyman]

The UK deployed 3 versions of their implementation of the Hispano: the Mk I (on the Hurricane) and Mk II (On Typhoon, Spitfire and early Tempest) and Mk V which was the short barrel version of the gun on the Tempest and Spitfire F22 and F24.

I think the Mk.I might have been found on any of the early Hispano-carrying aircraft. Though by the time any of the (British) Hispano aircraft started seeing any real service Hispano Mk.II production was well underway.

Lighter reciprocating parts (or entire gun) would help the rate of fire?

I don't think there was much lightening done in that department -- most weight saving was in the barrel and body -- but the modifications to the gas plug might have been all that was required. The buffer spring was strengthened as well.

The original French gun (and British copy, the Mk.I) fired at about 700 rounds/minute, but after various trials in 1939 it was found that reliability and breakages were greatly improved if the rate of fire was kept down to about 600 rounds/minute -- so this was specified in the Mk.II gun.

The same thing played out in the development of the Mk.V -- initial rate of fire was 820 rounds/min, but this was toned down to 750.

 

[ThomasP]

I ran across 2 UK manuals for the 20mm Mk I and Mk II a number of years ago, and the stated ROFs were the same for both. One UK manual listed 650-675 rpm when using the 60 round drum, and 590-620 rpm when using the belt feed. The other UK manual listed 650 rpm. The US manual TM 9-227 for the 20mm M1 and M2 lists ROFs of 600-700 rpm. The US manual TM 9-229 for the 20mm M3 lists 650-800 rpm. The US manual TM 9-2006 for the 20mm M24 (M3 modified for electrically fired primer ammunition) lists 700-800 rpm.

 

[A.G. Williams]

Tony, since you're here - is there a manual for the Hispano V available for easy download?

I have one in book form for the Mk I and Mk II, but not the Mk V.

 

[tomo pauk]

Your claim is that shortening the barrel was done for reasons of increasing rate of fire rather than aerodynamics. Apart from contradicting a expert in this thread...

Quote my post where I'm contradicting an expert in this thread with regard to the connection between barrel length and rate of fire on Hispano.

... there are two arguments against this:
1 The Full length US Hispano, All 2.45m of it, known as the M1 achieved a cadence of 700rpm which is 100rpm greater than the full length British versions of the same time. I'm not even sure what the ROF of the Hispano 2 was, it seems to have increased. It may have been greater than 600. The latter US M2/M3 versions were shortened like the Hispano V.

2 Unlike the Oerlikon the Hispano fired from a locked breech bolt. When the round being fired eventually passed a gas port which channelled gas back to a piston that was used to unlock unlocked the bolt. Residual gas pressure then ejected the spent cartridge casing against the bolt.
By contrast the Oerlikon's API mechanism fired while the bolt was moving forward, the mass of the bolt had to be high to slow the bolt enough and arrest the the recoil and this created a trade of between cadence, muzzle velocity and weight.

1 - 700 rd/min for Hispano I/II is cherry-picking the best scenario. This is what Tony Williams says (from here; my bold):
Compared with other Second World War 20 mm aircraft cannon, the Hispano was a powerful and effective gun, but only averagely fast-firing and unusually long and heavy. Its weaknesses were addressed in the late-war Mk V, shortened, lightened and speeded-up from 600 to 750 rpm.

2 - Nobody is disputing that.

The Mauser MG151 used a short recoil. The bolt was locked with the barrel like the Hispano, however after firing the motion of the barrel unlocked the bolt after a short recoil (instead of gas). The barrel then stops quickly but the bolt continues backward (via inertia and residual pressure) to allow extraction and reloading. This mechanism has less of a trade of but it also has the advantage of firing from a closed bolt that helps synchronisation.

So, after all the bolt was locked on MG 151 vs. your claim (my underscore):
The Oerlikon Mechanism API mechanism and that of the MG151 were recoil operated. The non locking bolt was heavy but served to buffer recoil which helped keep installed weight down.

The Gas channels in the Hispano represent an area that needs cleaning because it is vulnerable to fouling as well as being a complication.

Gas tubes, while not being complicated at all, were there so the cannon can actually operate, while giving a substantial increase of RoF vs. then-current mainstream big Oerlikon. In other words: no gas channels = no Hispano cannon.
Everyone knew that gas tubes need to be cleaned, it was not rocket science even in 1930s.

 

[A.G. Williams]

Lighter reciprocating parts (or entire gun) would help the rate of fire?

A combination of lighter reciprocating parts with stronger (or extra) recoil springs is the universal way to increase RoF. With gas operation (including the Hispano) a lot can be done with the location and size of the gas port: the closer it is to the chamber, the faster the bolt will unlock.