Cannons vs. MGs - the Reliability Angle

Discussion in 'Weapons Systems Tech.' started by Demetrious, Jun 11, 2010.

  1. Demetrious

    Demetrious Member

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    It's telling that when I came to the forums today to make this topic, I found yet another thread that had been derailed into the age-old cannon vs. MG argument. And as usual, all the same arguments are given their spin- rate of fire, destructive power, etc, etc. And eventually, as they always will, the science nerds will emerge with their slide-rules and spreadsheets and lecture on how X cannon delivers Y joules of energy to the target over Z time, utterly establishing their superiority.

    As usual, completely absent from the discussion is the simplest consideration- mechanical reliability.

    Guns jammed in WWII- they jammed often. Sometimes this was the fault of odd mountings (P-51B), or especially problematic weapons (Hispano,), but even outside of those examples, guns jammed with frequency. Now if you consider an aircraft with the all-cannon armament that is so frequently advocated- two 20mm Hispanos to replace 4 .50 cals in the Wildcat, for instance- one gun jamming will deny you 50% of your firepower. With the 4 M2 Brownings, a single jam will reduce your firepower by only 25%, and in a six-gun plane, you only lose 16%. And got help the cannon-armed plane if two guns jam.

    Many of the criticisms thrown at the US Air Forces for failure to adopt 20mm stem from the high performance of the 20mm Hispano cannon, a gun that combined M2-like ballistics with a cannon's firepower. In this weapon you seemingly find a destruction of the old machine-gun defense of "longer range, better ballistics." Well, consider the commentary of a Russian fighter pilot on the reliability of the Hispano:

    This isn't exactly news, of course- the finicky nature of the Hispano isn't a great secret. This perhaps can explain the US Air Force's inability to manufacture a home-grown version of the cannon.

    Now this covers the main point, but this former Soviet fighter pilot makes some other points that put some badly-needed practical perspective into the entire cannon vs. MG debate:

    The effectiveness of rifle-caliber guns is consistently underplayed, to say nothing of 12-13mm:

    Against German fighters, little firepower was needed to score effective kills:

    This is an obvious point that is consistently overlooked. While much is said of Germans requiring cannons to dispatch bombers, little is said of the lack of pressure on the Allies to adopt cannons. Almost all of us have seen an Bf-109 in person- as surely as Muslims trek towards Mecca, plane geeks trek to aviation museums- and once you've seen how small the Bf-109 was, you can appreciate why it took little firepower to down.

    Contrast that with the planes the Germans faced. Speak nothing of bombers; they were butting heads with armored beasts like the P-47 and the Il-2. The LaGs and Spitfires might be as fragile as a German ride, but the Yaks, P-38 and 51, and so on were at least modestly more durable.

    And the most important point this Russian fighter pilot makes in the entire interview:

    Ballistics don't count for diddly when you're shooting from point-blank range.

    It's common knowledge that most pilots made their gun kills from point-blank range, and that they were instructed to try for a point-blank shot if possible. Given the difficulties of aerial gunnery, and the fact that most defeated pilots never saw their attacker, this was more then possible.

    In short, in this Russian fighter pilot's experience, if you were in a proper firing position- i.e. firmly latched onto Jerry's ass- you could kill him with anything. .303, .50 caliber, 20mm, 37mm. I think we'd do well to remember this basic fact in any discussion of fighter armament.

    That's just my two cents, ladies and gents. Hope it was worth reading.
     
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  2. Glider

    Glider Well-Known Member

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    I cannot comment on the additional reliability of the ShVAK cannon but I can say that the 2TAF between June 1944 and May 1945 fired 13,500,000 rounds of 20mm from its Mk II and Mk V cannons with an average stoppage rate of 1 per 1,562 rounds of which approx 50% were stoppage feeds not problems with the gun. That may not be as reliable as the Russian gun but it seems good enough.

    Over the same period the 2 TAF fired 2,800,000 rounds of 0.50 with an average of one stoppage per 3,400 rounds, again pretty good.

    US built 20mm guns and ammunition were dreadful and despite many thousands of weapons being supplied to the RAF via lend lease not one was fitted to RAF aircraft, and in Malta US 20mm ammuition was destroyed despite the desperate shortage of all supplies.

    Re the effectiveness of the LMG. I am going from memory here the RAF checked the effectiveness of the 303 against an Me109F. They fired about 300 rounds at the 109 from the best firing position ie behind it and of the Approx 300 rounds only 4 did what they called fatal damage to the aircraft or pilot and another 8 would have hit the pilot in the leg or arm. As a result the RAF considered the 109F to be very well protected against the LMG.

    The reliability numbers came from 2nd Tactical Airforce volume 4 Weapons and Tactics pages 604-606. As I said the comments on the 303 vs Me109 are from memory after reading the official test report, but I am confident that they are close
     
  3. Demetrious

    Demetrious Member

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    #3 Demetrious, Jun 11, 2010
    Last edited: Jun 11, 2010
    That's also late war, with a lot more time to work out the kinks in the system, and they weren't flying as much "under pressure" for high turnaround times on aircraft, like during the BoB.

    The Oldsmobile 20mm cannon mounted on early P-39s worked fine, though it's ballistics put it firmly in 'tater chucker territory. All attempts to mimic the Hispano failed miserably, as you say.

    One .303 machine gun does not do the density of fire of six or eight .303 machine guns justice. Given the Browning .303's rate of fire was roughly 1200 RPM, then 300 rounds means that single gun fired a 15-second burst in testing. Conversely, six guns firing a total of 120 rounds a second (20 rounds/sec per gun, for 1200 rounds per minute,) could put that much firepower on target in 2.5 seconds. Now eight guns, the standard early-war outfitting for Spitfires or Hurricanes, could put out 160 total rounds/second. They'd put 300 rounds on target in about 1.8 seconds. A sustained 3-second burst from them would deliver 480 rounds. A 5 second burst, 800 rounds, which would most certainly shred the target.

    If you scale the "lethal" bullets, then that's 32 rounds either in the engine or the pilot after a 3 round burst, which I think is sufficient.

    Naturally, the caveat to this is that if you're saddled up on Jerry's tail, you will have the oppertunity to hose him down with a long 5 second burst. Naturally this feeds back into my above point- if you fired from the position that most pilots did, even LMGs would do the trick. 13mm and cannons would do it far better, naturally- nobody contests that- but even the much-maligned LMG was lethal at that range.
     
  4. claidemore

    claidemore Member

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    I agree that any weapon, LMG, HMG, or cannon will do the job at close range, but the folks selecting weapons can not limit their pilots to point blank firing positions only. They need a weapon that has a good chance of success at longer ranges as well. LMG's lose energy at longer ranges, 37mm cannons have rainbow trajectories. High velocity 20mm (Hispano and ShVAK) or high velocity HMGs are the obvious choices.

    The Soviets took the lmgs out of some Yak1's to lighten them and gave those single 20mm ShVAK armed Yaks to 'free hunter' pilots who achieved very high kill ratios with them.

    George Beurling used to concentrate on the projectile stream from only one cannon ( Spit VC with two of the four wing mounted Hispanos removed), ignoring the 2nd cannon. He was pretty successful with his 'single' cannon.

    One question though, why would the 4 x .50s in a Wildcat be replaced with only 2 x 20mm Hispansos? Wouldn't you put four of them in? Or a mix of two .50s and two 20mm as in the Mk XVI and XIV Spitfires?
     
  5. davebender

    davebender Well-Known Member

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    5 seconds is a very long time to maintain a firing position on an enemy fighter aircraft.
     
  6. claidemore

    claidemore Member

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    I thought so too, so I checked some gun cam footage on Utoob. 3-4 seconds seems to be the most common, but there's plenty of longer ones. 5 seconds is not uncommon and even longer times of 8-9 seconds can be found (fighter vs fighter).
    One German newsreel gave me pause for thought. It showed several attacks on Spitfires with 109s getting hits, but in each case the Spitfire gradually pulled out of the frame. There was no footage showing Spitfires that had catastrophic failures, explosions etc. Don't know if that means they just didn't have any footage availabe for that particular newsreel that showed conclusive kills, or if they chose not to show them, or what. There was one scene showing what appeared to be a Lysander under heavy fire. He was still flying as well.
    Here's the link.

    View: https://www.youtube.com/watch?v=HAYMI5Byfmw
     
  7. Demetrious

    Demetrious Member

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    Precisely. Just because most of your pilots won't necessarily need it doesn't mean you pass up the best option going. All I'm suggesting is that the difficulties of the "lesser" armaments have perhaps been... exaggerated.

    Mostly for weight savings (some of which could be traded for more ammo,) since the Wildcat had regrettable power/weight ratio.

    If my kiddie video games are any indication, it's entirely dependent on who you're fighting. Against an awake, alert, competent pilot, it's an eternity. Against somebody who didn't know you were there till you knocked, not so much, as claidemore saw on youtube.

    That sounds about right for early-war armament of 109s. The two 13mm guns were quite sufficient for downing Spits, but you wouldn't blow the Spit apart so much as riddle the engine and fuel tanks, leading to a "slow death," where the pilot bails from a plane that won't make it home, but wasn't blown apart instantly in a nice dramatic fashion.

    As to why the cannons weren't being used, the BoB 109s didn't have much cannon ammo, so the pilots were either out of ammo, trying to save ammo, or just making deflection shots that the early German cannon's ballistics weren't game for, I'd guess.
     
  8. claidemore

    claidemore Member

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    That newsreel was Dec 1941, so that would be 7.92 lmgs, not 13mm. The channel gruppes were flying either E7's or F2's during 1941, with a few F4's showing up in the fall and early winter.
     
  9. Glider

    Glider Well-Known Member

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    I would certainly disagree with your comment about not working under pressure as the 2 TAF often flew many sorties per day. You are correct about the late war but the 20mm was used extensively in the Far East and Desert which are as hot and dusty as you can get without any significant problems. The only time that I know of where adverse comments were made about the 20mm was at Malta where the problem was identified as being from the USA supplied 20mm ammo. Once this was destroyed the problem went away.



    You stand no chance of hitting any enemy fighter the size of a 109 with 300 direct hits from one burst. Even if you are right on top of him the guns are in the wings and synced to converge at a distance of around 250 yards away. Even in this ideal situation a large number of your bullets are going to miss, your guns are in the wing and most of them are going to be pointing at the 109's wings which are moving about. Your aircraft is unlikely to be flying striaght and level which puts extra dynamics into the situation.


    It could be lethal but the probability was that it wouldn't be. I think it was the Germans who called the LMG's door knockers, as all they did was let them know you were there. Plus it was the Russians who decided that one of the major problems with the Hurricane was the 303 which was so ineffective that they replaced them with 2 x 20mm and 2 x HMG.
     
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  10. Kurfürst

    Kurfürst Banned

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    #10 Kurfürst, Jun 12, 2010
    Last edited: Jun 12, 2010
    There is a fair bit of danger in reverse-engineering why certain decision was made. Of course everyone thinks of the big B-17 ec. interceptions over Germany in 1943-45, and applies that to the cannon vs. MG arguements, but it is a fact that the Germans (and Russians, French) adopted the idea of cannon armament much earlier.

    Cannon armament, including using a massively powerful 20mm MG C30 cannon (the same one as the Flaks, and light Panzern used) was considered for the original mid-1930 German fighter tender that in the end resulted the acceptance of the 109. The cannon was adopted for the 109E (and already designed for some earlier variants), when the LW's bomber fleet was the largest in Europe, and Germany was the least exposed to enemy bomber threat which at the time were composed of similiar twin engined medium bombers like the Germans had. They simply took a different approach to the subject, along with the French (probably influenced by the French btw! Again the problem of hindsight - in the 1930s, the German army, navy etc. was arming against the French, not the Brits, not the US etc!! ) who started adopting engine cannon with their Hispano. And the 109F, which finally switched to a single engine cannon, was designed in 1939, and went into production in 1940... no Fortresses over the continental sky... most of the time, not even Blenheims as a matter of fact... and no Sturmoviks.

    The same hindsight with US fighters, and that they mounted .50s because they would only have to deal with Jerry/Jap. fighters.. not true... again the P-38 (mounting a cannon btw) was designed as a long range interceptor, specifically for US needs. The P-47 was again designed as an interceptor, not as an escort fighter - early variants had the range of the 109 or Spitfire! Their armament of fifties were already choosen at this time, and was meant against bombers. BTW - the P-47 wasn't an "armored beast". It had a modest amount of pilot armor, typical of any fighter. Of course it was a big airframe, more difficult to tear apart, but then again, cannons were adopted many years before it first turned up.

    The British simply didn't have a working cannon in the 1930s, and opted against the .50s. So they started mounting a lot of LMGs. Again, Spits and Hurris were interceptors, designed to take down bombers, and not fighters. In any case, the large battery of LMGs wasn't a bad idea at the time (few, if any aircraft were armored), but quickly become obsolate since LMGs simply doesn't have the punch to penetrate armored, vital parts of the aircraft, and its kind of a sucker since the whole point is that so many rounds fired are bound to hit something vital - except if they are stopped by armor. So the Brits did the reasonable thing and adopted cannon, under the pressure from the experience from armored German bombers (and not vica versa!).

    BTW, speaking of guncam vids, I just foun this German newsreel of bodenplatte a couple of days ago.

    View: https://www.youtube.com/watch?v=Psh-HgAO_aE

    From around 0:45, they show some attacks on bombers... it looks really bad. I guess its MK 108 at works... it just looks far bigger than the flashes I've seen from earlier clips, where the attacking type was stated, and was surely with 20mm guns..
     
  11. davebender

    davebender Well-Known Member

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    The 3cm Mk108 cannon would work much quicker in such an ambush situation. No need to "saddle up" behind the enemy for 5 seconds, exposing yourself to attack by his wingman during that time.
     
  12. Glider

    Glider Well-Known Member

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    These are very interesting views. The Spits seem to be Mk V and the Hurriebombers would tend to support that timeline. In this case the weapons on the Me109 are likely to be 1 x 20mm and 2 x LMG. If the cannon ae not firing I would say that it supports the view that the LMG was pretty usless as the vast majority of those aircraft got away. Also the vast majority of those shots were missing the target despite the close range and centrally mounted guns. A five second burst on target is almost impossible.
     
  13. Demetrious

    Demetrious Member

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    #13 Demetrious, Jun 13, 2010
    Last edited: Jun 13, 2010
    All I meant by that was that the armorers had sufficient time to service the weapons, instead of having to get the same plane into the air again in six hours. Pressure is always present in a war.

    This not only contradicts everything I have heard about the Hispano's tight tolerances, but everything I know about firearms in desert environments in general. To be fair to both sides of the argument, however, a lot of "what you hear" isn't necessarily so. (Pilots who had one jam out of ten engagements might rate a gun poor out of sheer frustration, for example.)

    Given that pretty much every pilot account I've read- including the ones from that Russian pilot upthread- state that .303 and similar calibers lost most of their effective punch by 250-300 yards, I find it highly unlikely that they were setting their convergence past 100-150 yards. Especially considering that they trained the average pilot to fill their windscreen with enemy before firing.

    You still have a point with convergence, though- that same Russian pilot stated explicitly that the wing mounting of the guns in his Lend-Lease Hurricane was a royal pain in the ass because of the "dead zone" it created in front of the nose. Even with 100 yard convergence set, at 40 or 50 yards some of your guns will be missing. On the other hand, the rest can be applied with scientific precision.

    No, that was the appellation they applied to their 37mm anti-tank gun, because all it did versus T-34s was announce its presence. Still, I find your assertion that "they could be lethal but probably wouldn't be" to be rather odd. Are you implying that a battery of eight .303 machine guns at combat ranges would only knock down a Bf-109 through luck? :rolleyes:

    (Note the close range and the fact that this was probably with a Russian I-16, with center-mounted guns. Of course, the interviewer states that British pilots in the BoB reported similar results. Analyze as you may.)

    So they up-gunned their fighters, just like everybody else in the war? Big surprise. In fact, this feeds into this comment:

    This was a necessary observation- if you have the choice of hitting your opponent with a stick or with a sledgehammer, you take the sledgehammer if at all possible. I'm not claiming that LMGs were good- there was a reason every air force that used them upgraded to HMG or cannon- but if you honestly think they were useless... I'm not quite sure what to say.

    That reflects on the battery, not on the gun. Six or eight are sufficient, but two are not. It's the same amount of firepower a Sopwith Camel brought to bear, after all.

    This is one of the best posts I've seen on the board, and I mostly agree with your points here. The one exception is with the US Fighters- the P-47s eight .50s proved to be a tremendously powerful battery in it's own right, certainly sufficient for interception, as well as the P-38s battery. The fragility of their opponents I advance as a reason they kept these armaments. Interestingly enough, the US Navy (with the most fragile air opposition of all) wanted to move to all-cannon armaments, but I suspect this was as much because of their increasing ground-support role as anything.

    Another thing you made me realize is that the German choice of cannon armaments was probably as much an engineering decision as anything- again, observe the small size of the Bf-109. Where on earth are you going to cram in a 4 or 6 gun battery? The wings are very thin, and the cowling just doesn't have room. Your only options are the propeller hub, the top cowling and the wing roots. I suspect the cannon choice was motivated by the need to fit the most firepower into the smallest volume possible.
     
  14. Shortround6

    Shortround6 Well-Known Member

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    As far as reliability goes:

    Not every bodies machine guns had the same reliability.

    Not every bodies cannon had the same reliability.

    The same weapon in different installations had different reliability.

    The same weapon in different climates had different reliability.

    Reliability being the gun firing when you wanted it to and continuing to fire when wanted as long as the ammo held out and the gun was not abused by being over heated.

    The Hispano is a particularly hard gun to pin down.
    Made by three different countries, although information on French use or possible troubles seems to be scarce, this means it was made to 3 different standards. It used at least two different feed mechanisms. It was designed to be bolted to 500kg engine and needed a stiff mounting or cradle in order to do it's best if not mounted on an engine. Turning drum feed weapons 90 degrees onto their sides as in early Spitfire installations doesn't help either. How much trouble did Whirlwinds or the first 400 Beaufighters with drum feed guns have?
    There is no question that the Americans managed to foul up their version of the Hispano and continued to do so even when shown the solution.
    The Hispano and the American .50 cal Browning probably saw the widest variation in climate conditions of any aircraft guns. From the arctic to the North African dessert to the south east Asian jungles plus extensive sea service.

    Reliability in taking down an opponent is another subject called effectiveness.
     
  15. davebender

    davebender Well-Known Member

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    The MG151 cannon saw use in just about every environment. 800 were supplied to Japan to arm Ki-61 fighter aircraft. France used some after WWII. I suspect Israel did also in that half-baked Me-109 variant they purchased from Czechoslovakia. The MG151 was primary weapon (in triple mount) for the Sd.Kfz 251/21 flak half track. I suspect quite a few from shot down German aircraft also ended up on improvised Heer mounts.
     
  16. Glider

    Glider Well-Known Member

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    #16 Glider, Jun 13, 2010
    Last edited: Jun 14, 2010
    I understood maybe incorrectly that the point of the thread was to compare the russian 20mm to the Hispano 20mm as the Russians thought that the home grown weapon was more reliable. The actual figures (Not Heresay) for the later war period showed the Hispano to be reliable. You then questioned the reliability in the earlier part of the war and I made the observation that the only specific problem that I had heard of or knew about was at Malta (as documented in Malta the The Spitfire Years) was a problem with the American Ammunition. Of course the desert is an inhospitable place for any machinery but if you have any examples of specific problems with the Hispano compared to other weapons then please post details.
    Convergance distances varied by country, airforce, unit and often by personal preference. The fact that the LMG loses its impact at distance in well known ut 250 yards give or take was a common distance.

    Scientific precision is in my honest opinion wildly optimistic. Look at any combat film there are plenty available on the internet and see how many hits there are to the number that are fired. To hit another aircraft is difficult and a feat that vast majority of pilots failed to master.
    To a large degree, yes. The tests on the 109F proved that out of about 300 hits only 4 inflicted terminal damage to the target, roughtly 1 in 75 hits. The chances of getting 75 hits on an enemy target with one burst are minimal, so yes, luck will play an important part. To add to this we need to remember that later aircraft were even more robust. You could blaze away all day at a P47 from the rear with an LMG and would still need a lot of luck to actually shoot it down. You could blaze away all day at a P47 with an LMG and would need some luck to down it
     
  17. Kurfürst

    Kurfürst Banned

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    AFAIK a locally built version was also used on South African combat helicopters.
     
  18. Markus

    Markus Banned

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    If one defines "little firepower" as 8 to 12 RCMG with a 50/50 mix of AP and incendiary bullets that is true. Not just for german fighters but IMO single engine a/c in general. But twin engine a/c are an entirely different matter. I don´t know what ammo mix Hurricane based on Malta used in 1941 but they had a lot of trouble shooting down Ju-88. In more than one case they expanded their entire ammo supply and got a smoking engine in return or less!

    A cal.50 Browing plays in a different league. The bullets are more than four times as heavy as a cal.303/30-06/8mm and the cinetic energy is up to six times greater. With half a dozen and more of these very powerful weapons and no B-17 as a target one simply does not need cannon.
     
  19. Jabberwocky

    Jabberwocky Active Member

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    You do know that the "Oldsmobile 20mm cannon" was a license built Hispano, don't you? :shock:
     
  20. Snautzer01

    Snautzer01 Well-Known Member

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