UK goes all-in on a HMG class gun in the mid-30'ies

[RCAFson]

Although they all got CS props for the battle of Britain the issue of time to climb still remained. In October 1940 the LW were sending Bf109s across the Channel at 30,000 ft to bomb London, at high altitude with limited power weight is a big issue.

12lb (combat) overboost was permitted by the time of the BofB and, IIRC, the code for a squadron climb to altitude using 12lb boost was 'Buster'.

 

[ThomasP]

 

[A.G. Williams]

The Gsh-30-1 is an impressive achievement, in its simplicity and compact size. For me, the WWII equivalent to the Gsh-30-1 is the Berezin B-20.

To give a more direct comparison, the gun to look at is the Rheinmetall MK 103. This fired 30 x 184B ammo which was a close match in size and power for the Russian 30 x 165. But the MK 103 at 141 kg was three times heavier than the GSh-301 and only fired at one quarter of the rate (c. 400 rpm). Which means that the GSh-301 is twelve times better than the MK 103 in its destructive power per weight ratio. How much of the GSh's advantage is down to better design or better materials I don't know, but this suggests it wouldn't be easy to make anything like the GSh-301 in WW2.

 

[A.G. Williams]

The RN compared the Vickers .5in and the Browning .5in during comparative trials for a quad .5in naval AA mounting. The Vickers gun was chosen because it was more reliable:
"

1. Greater reliability
2. Wear and failure of parts – if any – are to minor parts that can be readily replaced.
3. Care and maintenance is easier to the inexpert, on account of its less complicated recoil and buffer mechanisms.
4. The mechanism and functioning of the gun requires less special or expert knowledge to obtain a good, reliable performance, and is more readily understood by the average seaman, who already receives training in the similar mechanism of the .303-inch gun.
5. Readily converted to right or left gun.
6. From a general technical point of view, it is the opinion that the fundamental principle of the mechanism and the action of the Vickers gun is superior to that of the Browning, and is more certain in its action generally.

The .5-inch Vickers gun is therefore recommended for the Naval service in preference to the Browning gun." (Small Arms Review V15N4 (Jan 2012), Volume 15)

I am slightly suspicious of this report - I suspect that the RN was familiar with the Vickers which made the testers view it more favourably.

In its original .303 form the Vickers had a reputation for being just about unbreakable but prone to stoppages for a variety or reasons. I understand that a standard item of gunners' equipment was a mallet, which the gunner used to whack the beast to keep it functioning... In the aircraft version this was just about possible for cowling-mounted synchronised guns, but the Vickers could never be wing-mounted as the gun wasn't reliable enough and needed to be within the pilot's reach. Only when the Browning arrived did the RAF feel confident enough to put the guns out in the wings. This is all for .30/.303 guns, but it suggests that the .5" Vickers aircraft gun (illustrated above) may have experienced problems.

 

[Shortround6]

In its original .303 form the Vickers had a reputation for being just about unbreakable but prone to stoppages for a variety or reasons. I understand that a standard item of gunners' equipment was a mallet, which the gunner used to whack the beast to keep it functioning... In the aircraft version this was just about possible for cowling-mounted synchronised guns, but the Vickers could never be wing-mounted as the gun wasn't reliable enough and needed to be within the pilot's reach.

Cut away of a Maxim gun. The Vickers turned the toggle over. Manual for the Vickers is supposed to have listed 27 (28?) different stoppages, most of which could be diagnosed by the position of the cocking handle when the gun stopped. Many of the stoppages could be cleared by healthy tug in the appropriate direction on the cocking handle, and/or a good whack with a gloved fist/mallet as already mentioned. But as Mr. Williams as said, you could not do that with wing mounted guns.

The 1920s trials were for AA guns and the gunner/gun crew had better access to the guns for fast remedial action.

As far as burning up barrels goes.
The standard M2 aircraft gun 36in barrel was supposed to go 10lbs.
The HB ground gun 45in barrel was supposed to weigh 27.4lbs.
The water cooled 45in AA gun barrel was supposed to weigh 16lbs. That is just the barrel, The water jacket (separate from the barrel) held 21lbs of water and was connected to a water can with hoses.

Like has been said earlier, the US chrome plated the barrels sometime during the war (I believe the Russians did too) and finally went to stellite inserts/liners.
The advantage for the US was they could build any of the 3 different guns on the exact same receivers or turn one into another in field armories if they had the right barrels and barrel jackets and buffer springs/parts.

 

[SaparotRob]

I spent way too much time watching that operate.

 

[BarnOwlLover]

I believe that a major source of jams on the Maxim/Vickers-Maxim was the same as on the Luger pistol (which used the same basic toggle lock system). That being that toggle lock mechanisms especially are known for being pretty sensitive to ammo variations. Lugers function great with pre-1945 German 9mm Luger ammo, but can function erratically with modern subsonic loads (intended for suppressed use) or modern hotted up SMG rounds.

Wouldn't surprise me if a Vickers or a Maxim would suffer from similar function problems with different ammo specs. Granted, most recoil or delayed blowback guns suffer from this, but toggle locks seems to suffer from it the worst (even gas operated guns can in certain conditions).

 

[z42]

In the late 1930s into 1940 there wasnt a reliable 50cal to get off the shelf.

That might very well be true. M2 and the FN variant thereof weren't close to ready in the mid-30'ies when the decision would have needed for it to be deployed close to the beginning of the war. And as discussed in this thread, the Vickers .50 might not have been suitable either.

I warming up to the suggestion of the 20mm Oerlikon FFL. That could have been ready and deployed in time, and provide a formidable punch.

Weight was of great importance, the total weight of all guns and ammunition.

Sure. Continuing the FFL speculation, the Spit/Hurricane Mk I carried about 80 kg worth of .303 guns (excluding ammo). For roughly that same weight, they could have carried a 2xFFL + 2x.303 armament (FFL was 30 kg). The later Spit V and IX could have gone for an all-cannon 4xFFL armament for roughly the same weight as the historical 2xHispano + 4x.303.

 

[Clayton Magnet]

I warming up to the suggestion of the 20mm Oerlikon FFL. That could have been ready and deployed in time, and provide a formidable punch.

Which still would have made more sense than the often repeated "what-if" suggestion that the RAF should have armed their fighters with 'Merican 50 Cals.
Quite frankly, armed with hindsight, the FFL would have been a better option than the HS.404. But the Hispano did eventually evolved into one of, if not the best, aircraft cannons on the war, in the Mk.V guise.

 

[pbehn]

Which still would have made more sense than the often repeated "what-if" suggestion that the RAF should have armed their fighters with 'Merican 50 Cals.
Quite frankly, armed with hindsight, the FFL would have been a better option than the HS.404. But the Hispano did eventually evolved into one of, if not the best, aircraft cannons on the war, in the Mk.V guise.

I dont know how much pilot input had to do with things ut I have heard two WW2 aces on was Geoffrey Wellum compare their "pea shooters" to a German 20mm cannon round, if you had been hit by a cannon shell or seen a colleague get hit by one, you wanted cannon yourself, yesterday if possible.

 

[Glider]

Which still would have made more sense than the often repeated "what-if" suggestion that the RAF should have armed their fighters with 'Merican 50 Cals.
Quite frankly, armed with hindsight, the FFL would have been a better option than the HS.404. But the Hispano did eventually evolved into one of, if not the best, aircraft cannons on the war, in the Mk.V guise.

I think it should be remembered that Germany replaced the 20mm FF cannon with almost indecent haste. They wouldn't have done that without a reason

 

[Shortround6]

Problem with the Oerlikon FFL is that you need to lay it over on it's side in a wing mount, like the Hispano. Apparently the Oerlikon had less trouble with this than the Hispano did.
What it took to sort out I don't know.
Next issue was the ammo capacity. They were drum fed and they were advertising different sized drums. Larger drums means a bigger bulge on the wing. Both the Germans and the Japanese did develop belt feeds it took several years after 1940 for them to show up. The Oerlikon's were not belt feed ready.
The Oerlikon's, at least the FFS used greased/waxed ammunition. The RN adopted the FFS as an anti-aircraft gun in 1938/39 and bought the license to manufacture and some initial batch/s of guns and ammo. Much of the order could not be delivered after France fell. Oerlikons were listed as proposed armament in a number of 1938-39 designs and this is not a mistake, or at least not always. However it seems like the RAF didn't like the greased/waxed ammunition as it gave trouble at altitude because of the temperature. Or it was thought that it would. Turns out the Hispano needed lubrication too.
The FFS guns on ships certainly used lubricated ammo.
I don't know how much work Germany and Japan did to the Oerlikon guns. German went to the trouble of changing the cartridge for the FF. Actual reason I don't know.
A number of countries trialed the Oerlikon gun/s but few aside from Germany, Japan and France actually bought any. The majority of Oerlikon sales seem to have been for the PZL 24 aircraft used in Greece, Turkey, Bulgaria and Rumania. Not all aircraft used by those countries got the cannon.
There was certainly a lot interest, but I don't know if it was a finished product or if many of those countries were beta testers

 

[Shortround6]

I think it should be remembered that Germany replaced the 20mm FF cannon with almost indecent haste. They wouldn't have done that without a reason

They had reasons.
1 was the slow rate of fire. Or perhaps slower than desired. Some other guns didn't shoot as fast as their advertisements said either
2. The FF had a low velocity, which makes it hard to hit with. However the FF was also light and you don't fire heavy projectiles at high speed without a heavy gun.

Let's also remember that propellent powders were also changing. What they could do in 1938-39 was not what they could do in 1933-35 and both were different than what could be done in 1944-45 depending on country.

The Germans also took a bit a detour with the MG 151/15. Very high velocity making it easy to hit with. But 15mm projectiles didn't hit that hard (compared to 20mm) the Germans went back to the 20mm shells. It also took quite a while to replace the 20mm FF cannon type.
The MG FF/M used lighter shells fired at higher velocity and used different springs (and perhaps breech block weight) to balance the firing. The basic gun hung around for years, perhaps in part because the MG 151 wasn't that easy to make (British thought it took more machining than a Hispano gun) and it took a long time to change the production lines over.

 

[tomo pauk]

I think it should be remembered that Germany replaced the 20mm FF cannon with almost indecent haste.

Did they, though?

Problem with the Oerlikon FFL is that you need to lay it over on it's side in a wing mount, like the Hispano. Apparently the Oerlikon had less trouble with this than the Hispano did.

So the problem was actually not present for the FFL?

Next issue was the ammo capacity. They were drum fed and they were advertising different sized drums. Larger drums means a bigger bulge on the wing. Both the Germans and the Japanese did develop belt feeds it took several years after 1940 for them to show up. The Oerlikon's were not belt feed ready.

Should we start with the Oerlikon in early 1930s, or wait for Hispano in late 1930s?
Oerlikon was at least offering bigger drums.

There was certainly a lot interest, but I don't know if it was a finished product or if many of those countries were beta testers

Early adopters

The Germans also took a bit a detour with the MG 151/15. Very high velocity making it easy to hit with. But 15mm projectiles didn't hit that hard (compared to 20mm) the Germans went back to the 20mm shells. It also took quite a while to replace the 20mm FF cannon type.
The MG FF/M used lighter shells fired at higher velocity and used different springs (and perhaps breech block weight) to balance the firing. The basic gun hung around for years, perhaps in part because the MG 151 wasn't that easy to make (British thought it took more machining than a Hispano gun) and it took a long time to change the production lines over.

There were places where the MG FF can fit easy, but the MG 151 cannot. Like in the wings of the Bf 109. The FF was also much lighter, and was using a more slender ammo, that also weighted less.

A belt-fed MG FFM looks like a low-hanging fruit in the hindsight, but indeed it took some time for that to materialize.

 

[Shortround6]

Probably from Mr. Williams website although uncredited.
From the left.
1. the early Oerlikon FF ammo or Becker cannon ammo
2. The Japanese FF ammo
3. The German MG FF ammo. MG FF/M uses the same case, projectiles may be different.
4. German MG 151/20 ammo. Same projectiles as the MG FF/M.
Skip 2 and go to the tall ones.
7. the Oerlikon FFS ammo. Can use the same projectiles as the #2
Skip 2, really tall ones
10. Oerlikon FFL ammo, same projectiles.
11, Hispano ammo, also can use the same projectiles.

Difference in cartridge diameter is not enough to get excited about.

Ammo for the US 20 mm Vulcan gun, Case is only 102mm long. Now we have a chubby case.

So the problem was actually not present for the FFL?

I don't know, we don't have many reports from German sources about the reliability/problems of the German guns, especially in English.
British may have done trials with captured guns but I doubt those were flying while pulling G loads (US .50s worked pretty good if you were flying straight and level

The Oerlikon guns used a heavy breech block (and yoke) slamming back and forth and maybe that worked, or that the since the gun was opening up with pressure in the chamber the cartridge came out with a bit more force. The Hispano was sort of combination. The gas system didn't really operate the gun, it just kept it closed as the pressure dropped a bit and allowed for a lighter breech block which could move faster (change direction) for the higher rate of fire. I am guessing and just throwing out possibilities. The Hispano, from some accounts, had problem ejecting/getting the empties out. Instead of falling out the bottom they went out the side and had to turn 90 degrees to go out the chute. If they got hung up, much like the US 37mm, you ran out of room real quick for the new rounds to go in because the last one is still stuck in the gun. Maybe they just needed to change the shape of the chute?

 

[z42]

I think it should be remembered that Germany replaced the 20mm FF cannon with almost indecent haste. They wouldn't have done that without a reason

They replaced the FF, but here we're discussing the FFL which didn't have the most glaring issue of the FF, namely the fairly modest muzzle velocity. FFL did have lower muzzle velocity than the Hispano, but I think it would have been sufficient for the duration of WWII. Of course there was a cost for this, FFL was a heavier gun than the FF (30 vs 23 kg), though the Hispano was even heavier (around 42 kg, which might even exclude the belt feed motors?).

[/I]The MG FF/M used lighter shells fired at higher velocity and used different springs (and perhaps breech block weight) to balance the firing. The basic gun hung around for years, perhaps in part because the MG 151 wasn't that easy to make (British thought it took more machining than a Hispano gun) and it took a long time to change the production lines over.

The requirement that the round and gun be very finely matched is AFAIU one of the drawbacks of the API blowback style design. That's why they needed the new MG FF/M when the mine shells were introduced, they couldn't be fired from the old FF gun. And conversely, the FF/M couldn't fire the old non-mine shells. (Though I don't know if the FF/M were new guns or was it conversion kits delivered to squadrons?)

The FF(/M) was used until the end of the war in applications like Schräge Musik as the low muzzle velocity wasn't an issue there, and hey, they had a big inventory of them lying around, why not use them.

Probably from Mr. Williams website although uncredited.
From the left.
1. the early Oerlikon FF ammo or Becker cannon ammo
2. The Japanese FF ammo
3. The German MG FF ammo. MG FF/M uses the same case, projectiles may be different.
4. German MG 151/20 ammo. Same projectiles as the MG FF/M.
Skip 2 and go to the tall ones.
7. the Oerlikon FFS ammo. Can use the same projectiles as the #2
Skip 2, really tall ones
10. Oerlikon FFL ammo, same projectiles.
11, Hispano ammo, also can use the same projectiles.

I think you have 7 and 10 mixed. The FFL was intermediate between the FF and the FFS.

The Oerlikon guns used a heavy breech block (and yoke) slamming back and forth and maybe that worked, or that the since the gun was opening up with pressure in the chamber the cartridge came out with a bit more force.

Yeah, I'm not really a fan of API blowback, but if that's what's available and works 1935-ish..

And to be pedantic, I'm not sure the chamber opened with more pressure than other designs, the entire idea of API blowback was that the round is pushed further into the chamber so that when it begins to move back the case is still supported by the chamber sides, and by the time the rear of the case clears the chamber the pressure has dissipated sufficiently. But maybe I'm misunderstanding what you're trying to say.

 

[Greyman]

Part of the problem was the lousy ammunition, During the BoB around 3 guns out of eight were being fed ball ammo which was pretty much infantry gun ammo, lead core, light tip, copper jacket or alloy. Didn't penetrate for crap and deflected easily. Two guns out of 8 had AP with steel cores. Depending supply either one or two guns had the good De Wilde ammo.

Minor aside: in testing it was AP rounds that were deflected more often -- the main issue being deflections of aircraft skin at shallow angles (ie: dead-astern shots). Against armour plate and heavy fittings AP was superior. Considering the lack of armour in German aircraft in 1939/40 I don't think there was much to choose between ball and AP ammo.

In my opinion being able to see 'de Wilde' flashes or holding fire until 150 yards or less would have ten times the impact on lethality as any minor difference in solid ammo.

 

[Shortround6]

holding fire until 150 yards or less would have ten times the impact on lethality as any minor difference in solid ammo.

Even holding fire until 300yds would have been a significant improvement. Gun camera footage of training showed some pilots opening fire at 900yds or beyond.
But that is training.
Better tactics would have improved things a lot even with the poor bullet supply.
But we are back to training (possibly, there is a claim they didn't have time to show the new pilots much more than follow the leader formations ?)

Using hindsight we can see that they often didn't provide armor protection against much more than the 7.62-8mm threat. To do so would have required an increase in armor weight of around 40-60% (?) and since the lighter armor would also save the pilot from shell fragments (both aerial cannon and flak cannon) they often didn't want to fit heavier armor.

 

[A.G. Williams]

What follows concerns naval AA use of the Oerlikon and Hispano, but it provides some pointers concerning reliability:

'...the Oerlikon offered greater reliability because of [its] greater reserve of power. It was operated by maximum gas pressure, about 23 tons per square inch, and by springs which were correspondingly powerful. On the other hand the Hispano-Suiza was operated by reduced gas pressure of about 8 tons per square inch and by springs which were similarly weak... the forces at work in the Oerlikon were consequently greater than those in the Hispano, and
hence such factors as friction, the effect of different elevations, cold weather, rain and the like, were too small in proportion to the operating forces to cause stoppage. Primarily as a result of this reserve power, the Oerlikon did not require skilled service maintenance. One of the greatest advantages of the Oerlikon... was [that] it had a barrel which could be replaced in about 30 seconds. Since an airplane gun fired very short bursts, and was mounted in the wings of a plane moving through the air at a high rate of speed, it did not present much of a cooling problem. The Hispano was therefore designed without any thought of permitting a change of barrels during action; in fact, it was hardly possible under such conditions. At sea, however, against multi-plane dive-bombing attacks, prolonged firing was necessary... The magazine employed with the Oerlikon was superior... the Oerlikon magazine could be kept fully loaded without any tension on the springs while in the Hispano the spring was compressed as long as the magazine was loaded, a condition which brought about occasional spring collapse. Secondly, the magazine had a greater reserve because of the easier task of feeding at 490rpm as against the Hispano's 690. Thirdly, the Oerlikon magazine had a straight tangential lead through its mouthpiece, whereas the Hispano had a 90 degree bend...'
The sea experience of the British with the Hispano-Suiza proved the superiority of the Oerlikon. After the fall of France supplies of Oerlikons from Switzerland were cut off, and as a stop-gap Hispano guns were installed on several escort vessels. The results were uniformly bad. Ships reported frequent stoppages from the unsatisfactory design of the cradle, salt water corrosion around the breech block, unlocked tappets, and the collapse of the magazine springs... when water got into a hot gun barrel stoppage was likely at the reopening of fire. The guns were so unreliable that one vessel reported that she preferred not to open fire with her Hispanos in the hope that the Germans would think that she was not a warship. Opposed to this, British experience with the 100 Oerlikons at sea in November of 1940 was uniformly excellent.'

This was from the USN Bureau of Ordnance (I copied it into Autocannon)

 

[z42]

Slightly resurrecting this thread, I found some new (to me!) information about the FN variant of the Browning HMG in that most reliable of all primary sources, namely the War Thunder wiki. Sweden bought them, including apparently a license and plans for manufacturing them. After Belgium was occupied, it seems the Swedes considered the licensing agreement moot, and gave the plans to Finland as war support. Finland then essentially pirate produced them as the LKK/42 (aircraft machine gun model 1942) and mounted them on the Finnish Buffalos, and were apparently happy with them. After the war when it was clear that time had drove past HMG's as aircraft armament they tried to repurpose them as light AA guns. This however proved to be a failure, as the high RoF, thin and light barrels, and lack of a high velocity slipstream meant that the barrels overheated very quickly. Sweden came up with a clever idea how to use their stock; they temporarily mounted them on their aircraft instead of the cannons for air gunnery training, as the ammunition was a lot cheaper than cannon shells (and less risk associated with spraying HE shells around the landscape, I presume). The guns were used for gunnery training in this way until the Viggen was retired in 2007. Also Finland copied this idea, and used their stock as aircraft training guns.

12.7 mm LKk/42 machine gun - War Thunder Wiki

wiki.warthunder.com