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20mm cannon better than .50 at everything?


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#1 epicenturic

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Posted 03 August 2011 - 0403 AM

I've been searching through these forums and the inter-net at large, for a while, trying to find out what is the proper use of 50 caliber machine guns as used by an army. From what I've discovered, their main use is anti-materiel and long-range shooting, with their suppressive effect being particularly good compared to full caliber rifle rounds. Now obviously, the US armed forces have huge numbers of M2s and loads of ammunition for them, so it makes sense for them to keep using them, but suppose, for a moment, that you're in charge of procurement for a military that doesn't have that baggage and can start with a clean slate. Would a 20mm cannon make more sense than using a 50 caliber machine gun in ground to ground roles? Something like this, for instance, that being the API Blowback action Oerlikon 20mm cannon. It's lighter than the M2, has a comparatively even recoil push due to its action, and would be much better than a 50 cal at anti-materiel tasks, with its suppressive effect probably being much better than the 50. The one drawback is that the ammunition would be heavier, but it's also considerably more effective per round, and one thing I learned from discussions on this site is that the ammunition for a 50 is too heavy to man-pack anyway, so it would be a vehicle taking regardless, which would mitigate that to some extent.

Now, I know there's some South African company making copies of the MG 151/20 for pretty much that purpose (or at least they used to), so I don't think I'm too far off base with this, but I also don't think that too many armies actually use 20mm cannons in this sort of role, so I'm not sure how good of an idea it really is.

Any thoughts on this? Or on why Soviet forces tended not to use 50 caliber machine guns as much as the US forces do? Where would a 20mm cannon be most useful in an army?

#2 Colin

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Posted 03 August 2011 - 0821 AM

Humping a .50cal was bad enough, humping a 20mm would be painful. Plus the ammo weight and costs

#3 seahawk

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Posted 03 August 2011 - 0833 AM

An on a vehicle mount the advantages of the 20mm are not that big. If you consider weight, size and ammo load in combination with the ballistic quality of the rounds.

Edited by seahawk, 03 August 2011 - 1433 PM.


#4 Steven P Allen

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Posted 03 August 2011 - 0903 AM

The effectiveness of an individual round is not decisive. How many rounds actually hit something? If you're looking for a Golden BB, use a single-shot. Otherwise, being able to carry more rounds--even a vehicle can carry only so many, the increase being both in weight AND in volume--has its advantages.

#5 Tony Williams

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Posted 03 August 2011 - 0948 AM

A simple question with a very complicated answer. In fact, many answers depending on the period of time and the use to which the guns were being put.

However, the simplest explanation for the continued popularity of the .50 BMG is to point out (as I have done before) that it hits a kind of "sweet spot" in the arsenal in being vastly more effective than rifle-calibre MGs in terms of effective range, barrier penetration and general mayhem inflicted on the target, yet the guns and ammo are cheap compared with 20mm.

So the .50 remains very popular, not for any particular task (too weak for AA or anti-armour, too heavy for sensible manpacking) but simply in providing economical, direct supporting fire to ground operations.

Arguably the 20mm has actually had its day (its peak usefulness being in WW2), because 25+mm cannon are very much more effective against the kind of targets which cannon are employed against today, and don't cost a great deal more.

#6 Heirophant

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Posted 03 August 2011 - 1548 PM

I am a layman, what I say is simply IMHO.

The functional tactical difference between a "machinegun" and an "autocannon" is the MG's ability to be man-handled into relatively tighter spaces (say through corridors and into small rooms, or in denser terrain) and up steeper inclines (say up stairs or narrow slopes). The autocannon would need to be set up in relatively more open areas (large corridors/rooms, or in the field), and man-handling up slopes would be a problem.

You also have to take into account a certain minimum effective number of rounds allocated. Obviously, the larger the caliber, the smaller the minimum can be, within limits.

An automatic weapons-system, meaning gun + tripod + ammo load, in order to be useful to infantry, must be just barely light enough such that it can be maneuvered and sited flexibly. "MGs" must be especially flexible, while ACs trade off a bit of flexibility in maneuver and siting for added killing power.

I see no reason why 20mm ammo should cost exponentially more than .50 cal, on the basis of cost vs. destructive power. The 20mm projectile is to the .50cal what the .50cal is to the .30cal. So yes, increased cost, but increased effectiveness.

The real problem is, I think, the weight of the 20mm if you supplied the weapon with the needed effective ammo load. You can lighten the gun (and you could apply the same techniques to lighten the .50cal weapon as well), but the ammo, to be effective, stays the same weight in both cases.

So while the Heavy MG can have the minimum number of rounds and still retain infantry mobility, the 20mm can't. So, going from say 7.62mm to 15.5mm, and reducing the ammo allocation would work, if only just. But going from 15.5mm to 20mm and FURTHER reducing ammo allocation would cross the threshold for minimum ammo load in an infantry application.

20mm machine-cannons have their place as support weapons; they generate a lot of firepower. But they can't replace the 12.7, 14.5 or 15.5mm heavy machineguns for deployability and total weight vs. utility, especially in the infantry support role.

Edited by Heirophant, 03 August 2011 - 1549 PM.


#7 EvanDP

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Posted 03 August 2011 - 1620 PM

A simple question with a very complicated answer. In fact, many answers depending on the period of time and the use to which the guns were being put.

However, the simplest explanation for the continued popularity of the .50 BMG is to point out (as I have done before) that it hits a kind of "sweet spot" in the arsenal in being vastly more effective than rifle-calibre MGs in terms of effective range, barrier penetration and general mayhem inflicted on the target, yet the guns and ammo are cheap compared with 20mm.

So the .50 remains very popular, not for any particular task (too weak for AA or anti-armour, too heavy for sensible manpacking) but simply in providing economical, direct supporting fire to ground operations.

Arguably the 20mm has actually had its day (its peak usefulness being in WW2), because 25+mm cannon are very much more effective against the kind of targets which cannon are employed against today, and don't cost a great deal more.


Also fitting in the "sweet spot" I think we would have to consider the Mk 19 40mm AGL. It seems to fit into the same but complementary niche as the .50 Cal. M2. The M2 gives hard hitting direct fire with good AP performance for it's size and the 40mm AGL gives a good volume of HE fire. Both give good value for the relative size and weight. The same could be said of the Soviet/Russian counterparts the 12.7/14.5mm HMGs and the 30mm AGL.

#8 Archie Pellagio

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Posted 03 August 2011 - 1744 PM

I never really understood 14.5mm Soviet and the Axis WWII era 15mm MG's - all the weight and effort of an auto-cannon, but without the punch, particularly the explosive punch that cannons delivered.

Always struck me as neither fish nor fowl.

As for why 12.7 not 20mm, well obviously it is going to depend on what platform we're talking about here.
At the bottom end of the scale a 20mm AMR is going to be largely pointless - what targets that can't be taken out by a .50BMG do you expect to regularly take out with a 20mm round in a semi-auto man-portable weapon?
On things like light vehicles, the size and complexities of 20mm cannon are largely either prohibitive (A perfect example is that 80's era project to put a 20mm on a humvee)or overkill.

On heavy light armour (LAVs etc) you can just as easily get larger cannon than 20mm if you want the full turret/sensors, or can just go light with .50 if infantry and light/unarmoured vehicles are your main target.

Edited by Luke Y, 03 August 2011 - 1745 PM.


#9 Typhoid Maxx

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Posted 03 August 2011 - 1800 PM

Not only is the forum under contributed to, but we get half the crap from General Air.




#10 Galen.Wright

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Posted 03 August 2011 - 1814 PM

On things like light vehicles, the size and complexities of 20mm cannon are largely either prohibitive (A perfect example is that 80's era project to put a 20mm on a humvee)or overkill.

Interesting.

It seems this idea has been revived because Iran is testing/deploying (one can never tell exactly which) a 30 mm 2A42 on a 3/4 ton general-purpose vehicle. It goes by the name "Tabas" but I'm not sure if this is just the truck or the entire system. The setup is about as basic as you can get - the guns is in a rotating mount with ammunition containers for the dual feed on either side. Who knows how practical or useful this system is though.

It's a bit bigger then what the OP is describing but it's basically the same thing which is an autocannon mounted on a light vehicle.
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#11 Jason L

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Posted 03 August 2011 - 1839 PM

I never really understood 14.5mm Soviet and the Axis WWII era 15mm MG's - all the weight and effort of an auto-cannon, but without the punch, particularly the explosive punch that cannons delivered.

Always struck me as neither fish nor fowl.


The 14.5 has quite excellent penetration compared to the .50 or russian 12.7mm. IIRC almost double at 500m if you discount sub-calibre projectiles. Isn't weight difference something like 30 lb? It's just another point on the continuum, arguably at less of a sweet spot than 12.7mm but I think it makes a lot of sense as a primary light vehicle armament when you don't necessarily have the volume for 25mm or 30mm ammo.

#12 wallaby bob

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Posted 03 August 2011 - 1853 PM

[quote name='Luke Y' date='03 August 2011 - 2244 PM' timestamp='1312411491' On things like light vehicles, the size and complexities of 20mm cannon are largely either prohibitive (A perfect example is that 80's era project to put a 20mm on a humvee)or overkill.

Luke. How about that 106MM RR on a Vespa motor scooter? I seem to recall it was a 50s or 60s idea.WB

#13 CaptLuke

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Posted 03 August 2011 - 2057 PM

I've been searching through these forums and the inter-net at large, for a while, trying to find out what is the proper use of 50 caliber machine guns as used by an army. . .


We had an interesting thread awhile back looking at it from the other side: Why use a .50 instead of twin .30? Many of the comments about using .50 are applicable to this line of thought (both pro and con). http://208.84.116.22...opic=32210&st=0

One thing to keep in mind is that .50 does not equal M2. Other weapons are much lighter and sometimes feature dual feed (one for "regular", one for SLAP).

The other is that the .50 is just about ideal for use against the "light material" category. Suicide bombers in cars and trucks, light watercraft, anything behind the walls of houses/buildings and so on are all much more vulnerable to .50 fire (especially with the new Raufoss rounds)than lighter calibers for much less weight and cost than even a 20mm cannon. Also if you go for a lightweight cannon in 20mm you still need a 25mm or 30mm round for serious vehicle mounted work and do you really want a 20mm supply chain and a 25/30mm supply chain?

#14 Heirophant

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Posted 03 August 2011 - 2300 PM

I never really understood 14.5mm Soviet and the Axis WWII era 15mm MG's - all the weight and effort of an auto-cannon, but without the punch, particularly the explosive punch that cannons delivered.



Interesting.

It seems this idea has been revived because Iran is testing/deploying (one can never tell exactly which) a 30 mm 2A42 on a 3/4 ton general-purpose vehicle.


The 14.5 has quite excellent penetration compared to the .50 or russian 12.7mm. IIRC almost double at 500m if you discount sub-calibre projectiles. Isn't weight difference something like 30 lb? It's just another point on the continuum, arguably at less of a sweet spot than 12.7mm but I think it makes a lot of sense as a primary light vehicle armament when you don't necessarily have the volume for 25mm or 30mm ammo.


There comes a tipping point with heavy automatic weapons where mechanical assistance is needed to aim and operate them. I think that's what I see in that picture of the Iranian vehicle with the 30mm autocannon. Mechanical assistance means system weight jumps up sharply, not smoothly or in linear fashion.

The tipping point is not yet reached with 12.7mm. Clearly, .50cal is able to be swung around, aimed and operated using just human muscle power. This also still applies to 14.5mm and the 15.5mm MG from Belgium - they can still do without hydraulic mounts or power assist.

Beyond 15.5mm, you cross the "threshold". IMHO, after 15.5mm, they cease to be infantry machineguns, and start tactically being autocannons.

#15 EvanDP

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Posted 03 August 2011 - 2343 PM

Interesting.

It seems this idea has been revived because Iran is testing/deploying (one can never tell exactly which) a 30 mm 2A42 on a 3/4 ton general-purpose vehicle. It goes by the name "Tabas" but I'm not sure if this is just the truck or the entire system. The setup is about as basic as you can get - the guns is in a rotating mount with ammunition containers for the dual feed on either side. Who knows how practical or useful this system is though.

It's a bit bigger then what the OP is describing but it's basically the same thing which is an autocannon mounted on a light vehicle.
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Is that a jack at the rear in the first photo? If it has stability problems when firing that it requires external support for the vehicle doesn't that reduce it's effectiveness. How useful is it if only the first round is anywhere near the target.

#16 Tony Williams

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Posted 04 August 2011 - 0241 AM

I see no reason why 20mm ammo should cost exponentially more than .50 cal, on the basis of cost vs. destructive power. The 20mm projectile is to the .50cal what the .50cal is to the .30cal. So yes, increased cost, but increased effectiveness.

The overwhelming majority of .50 ammo fired uses bullets which are basically scaled-up .30 bullets. They use more materials, but are no more difficult to make.

Cannon typically fire shells which are filled with HE and have sophisticated mechanical fuzes with all sorts of bore-safety and possibly self-destruct features. They are vastly more complicated to make.

Admittedly, this distinction has become blurred today because of the development of more sophisticated .50 ammo like SLAP APDS and Raufoss Multipurpose (which is made in much the same way regardless of calibre), but those are exceptions which probably only account for a tiny percentage of HMG rounds fired.

#17 DougRichards

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Posted 04 August 2011 - 0713 AM

I never really understood 14.5mm Soviet and the Axis WWII era 15mm MG's - all the weight and effort of an auto-cannon, but without the punch, particularly the explosive punch that cannons delivered.

Always struck me as neither fish nor fowl.

As for why 12.7 not 20mm, well obviously it is going to depend on what platform we're talking about here.
At the bottom end of the scale a 20mm AMR is going to be largely pointless - what targets that can't be taken out by a .50BMG do you expect to regularly take out with a 20mm round in a semi-auto man-portable weapon?
On things like light vehicles, the size and complexities of 20mm cannon are largely either prohibitive (A perfect example is that 80's era project to put a 20mm on a humvee)or overkill.

On heavy light armour (LAVs etc) you can just as easily get larger cannon than 20mm if you want the full turret/sensors, or can just go light with .50 if infantry and light/unarmoured vehicles are your main target.


Well, let us look at the one 20mm 'man portable' infantry gun that saw war servive - about 70 years ao - the Japanese Type 97 20mm anti-tank rifle. Effectively took 4 men to carry it and was really little more effective than the Boys Anti-Tank rifle against armoured vehicles and similar targets.

#18 Sardaukar

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Posted 04 August 2011 - 0747 AM

Well, let us look at the one 20mm 'man portable' infantry gun that saw war servive - about 70 years ao - the Japanese Type 97 20mm anti-tank rifle. Effectively took 4 men to carry it and was really little more effective than the Boys Anti-Tank rifle against armoured vehicles and similar targets.


Also things like http://en.wikipedia....wiki/Lahti_L-39 were not really "man-portable", Lahti L-39 ATR weight being almost 50kg...

#19 DanielStarseer

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Posted 04 August 2011 - 0802 AM

....

One thing to keep in mind is that .50 does not equal M2. Other weapons are much lighter and sometimes feature dual feed (one for "regular", one for SLAP).

....


Having seen in the last several years various attempts to lighten both the SAW/M249 (MK46?) and M240 (new M240L) series MGs (modifications which actually resulted in fielded systems),
it's interesting to note that not a lot seems to have been done to lighten the venerable M2.
Other than the recent limited-adoption of the M2E2 with some barrels improvements that supposedly eliminate the constant HS&T monitoring of the M2,
there doesn't seem to be much mention anywhere of incorporating newer materials to lighten the basic weapon.

Just seems odd that, since inception, the .30 cal MG in dozens of nations' services has considerably evolved beyond the M1919 Browning,
yet the .50 cal hasn't (even with promising designs like that "Dover Devil" which eventually inspired Singapore to develop and produce that CIS50).
(And even the *new* externally-powered 12.7mm Chain Gun variant is lighter than the Ma Deuce...)

Perhaps because it's generally accepted the heavy M2 (and its ammo cans) is more-often-than-not mounted to a vehicle,
but still,
countless checkpoints the world over for the last 3/4 century have ground-mounted ones covering their approaches (meaning someone hoofed it there on foot).

Would anyone really want to hoof around a 20mm auto gun?
Well, the US Army did have this notion of infantry carrying around that 25mm smart grenade MG (remains to be seen if the 12.7mm variant ever reaches active service: troops in trials seemed displeased with its relatively slow fire rate (not even 300rpm)).

#20 Wobbly Head

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Posted 04 August 2011 - 0831 AM

There is also the Legal issue, lawyers there worse than cockroaches. .50 cal and 12.7mm are the largest caliber that can be used directly against personnel without breaking the Geneva convention (yes I know they still debating that) 20mm is well beyond that especially the parts about using exploding bullets.




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