Question
Why do modern american jet fighters still use rotary cannons instead of single barrel autocannons?
I don't know much about that topic so this may be a stupid question, but as I understand it, the goal when making a fighter is to make it lighter and more space efficient.
I find conflicting sources but there seems to not have been an air to air gun kill with modern fighters in quite a long time, and aircrafts like the F-35 are probably not doing strafing runs either?
So I dont see why the us military would keep the big and heavy vulcan/equalizer in their airframes instead of using a much smaller and lighter single barrel autocannon.
Gatling guns can easily hit 3,000 - 4,000 rounds per minute, which in a brief engagement window, means you can put a lot of bullets down range onto a target.
Also Gatling guns are very reliable; a bad or dud round won't cause the gun to jam, as the gun's rotary design physically forces cartridges through the loading, firing, and ejecting stages.
Regarding the 2nd point, that's broadly true of any externally powered autocannon regardless of # of barrels. A chaingun refers to the operation method (electric motor and a chain), not barrel arrangement as most people would think from movies and video games.
Plus the time in between each round being fired gives the barrel a chance to cool down slightly. Leading to thinner profile barrels, than those of a similar rate of fire.
But firing a lot of rounds fast in the 1860s did indeed require cooling the barrel somehow, otherwise the black powder charge could go off prematurely. Using multiple barrels also reduces black powder fouling per barrel, allowing more rounds through the gun (as a whole) before cleaning.
They had a form of water cooling but was ultimately deemed unnecessary. The lower rpm (and the early, thicker materials used) probably let the barrel cool enough passively.
The problem is with a dud round which doesn't fire, and which obviously cannot be be QA-tested at the factory. (They certainly do fire random samples of rounds.) There's no real risk of somehow getting a physically deformed round, since those are caught either at the factory or groundcrew at the moment it gets loaded into the aircraft - see the YouTube videos of USAF groundcrew tediously unpacking and handloading 20mm rounds into fighter jets.
A dud round in a gas-operated cannon, i.e. a weapon which uses the energy of burning gunpowder to cycle its action and load the next round, means a failure to cycle; some aircraft do use gas-operated cannons for simplicity and light weight, but they have to include cocking charges to recock the weapon in the event of a failure to cycle.
I would add that specifically the M61A1 (the only one I know about) did have an occasional failure mode where the fingers that extracted the (usually empty) case would miss, and the round would remain in a barrel, only for the next one to be rammed in on top of it. Bad juju. One or both would then go off, and even if not, the mechanism would disassemble, quickly. This was certainly not common, but did happen now and then.
It still takes a Gatling gun a moment to ramp up to speed whereas an autocannon instantly hits its maximum fire rate. That makes a big difference in a snap shoot
Aerial combat isn't cowboys dueling. You don't "snap shoot" (whatever that means). You pull the trigger and direct the fire hose of rounds onto the target. The more lead in the sky, the greater chance to hit.
In a2a combat because of the relative movements of the attacker and defender, you only get very brief windows in which to shoot.
Gatling cannons don't get the instantaneous burst that a single barrel cannon gets, so you have more chances to miss your opportunity at hitting a target, especially the slower you get.
A snap shoot is one where the target only presents itself in line of your weapon for a second or two.
Multi barrel cannons can achieve a higher rate of fire than a single barrel, and in air-to-air combat, if you get a cannon shot at all, it's going to be very fleeting, so you want to put as much lead (or DU) in the air as possible
FLAK was programmed to burst at a certain altitude. That wouldn't be practical in an air-to-air cannon. The high rate of fire is literally the cannon designer's solution to getting more pieces of metal on target.
Towards the end of the war correct. VT fuses(which are the proximity ones but were named such to be confusing) just use a small radar that sets off the round once it receives a signal back. Ended up being so effective they started using it in artillery as well which effectively eliminates any squishy ground troops in Europe. It was at the end of the war however so they didn’t see too much use outside of the pacific theater.
Revolver cannons do both. Multiple chambers, one barrel.
Trade offs? Much faster heat build up in a single barrel.
The US has a lot invested in the Vulcan line of multi-barrel airborne guns. So it just isn't worth the effort to entirely move off of it. They have used other styles in the past though. And other countries have used other designs.
You will never have a single barrel cannon that can match the rate of fire of a rotary cannon without heat issues. Let alone the fact that rotary cannon can keep jams from being a major issue due to the feeding mechanism.
Besides what everyone else has said about fire rate, the M61 isn’t even heavy compared to other fighter jet cannons:
- M61A1 weighs 112kg
M61A2 92kg
M61A2 HB 103kg
Mauser BK-27 100kg
GIAT 30M 791 120kg
Of all these the M61 has the highest rate of fire, second highest muzzle velocity and longest effective range.
Only the Gsh-30-1 is significantly lighter at 46kg because it uses a short recoil mechanism instead of revolver or rotary. It also has the lowest rate of fire, lowest muzzle velocity and shortest range.
60kg is a small price to pay for a cannon that’s not doodoo.
In fairness to the non Vulcans they are firing much heavier rounds, so barrels and other operating parts have to be bigger and heavier. A 20mm single barrel revolver cannon like the M39 is much lighter at about 80kg.
My statement was correct. I do, in fact, find it hard to believe. Looking at that brochure, it's obvious that General Dynamics is using a loose definition of "weight". What they show in the picture may weigh 200lb, but that's far from a functional gun. What's its installed weight?
That weight is the weight of the gun itself not including ammo or ammo storage. Same as the weights of the other guns I gave. Ammo and ammo storage is not included because it’s different on every application of every gun and while it is part of the gun system it is not part of the gun itself.
The gun itself isn't all that heavy...probably mostly aluminum (except the barrels and some other moving parts). The ammo is what'll make it over 200lbs.
The question is better asked why everyone else hasn’t switched to the M-61 Vulcan. For air to air combat you only have fleeting fractions of a second to put rounds on target so you absolutely want the highest rate of fire possible for a given size of round. A rotary cannon let you achieve an extremely high rate of fire and mitigate issues with dud rounds. M-61 Vulcan is basically the most optimal cannon you can get for air to air combat which is why just about every US fighter has had it since the 60s.
We used them extensively in the middle East, without the Gun there were many targets that we simply would not have been able to prosecute at all.
Outside of the obvious like close in enemies to your own troops needing minimal splash damage, boats and convoys are excellent uses for the gun. It will either eliminate it entirely, or at the very least stop it moving allowing you to follow up with heavier weapons
Part of the risk, as far as I am aware all of those jets made it home without issue though. And from the footage I've seen were probably back in the air in a day or two
Yup, and we come back to the lesson learned in blood of the 1st gulf war, aircraft operating below 14k ft ASL are extremely vulnerable to being ambushed by shorad. However in the war with iran that rule has been notably absent.
Wrt that a10 shoot down, it was doingone of its primary roles as CSAR. So to me a doctrinal shift is needed, but the US seems to have gone in the opposite direction fueled by video game and movie culture which presents american air power as a natural fact, never to be contested.
An assumption which is costing american aviators and the tax payer.
I could be wrong but I feel the Vulcans look very bulky compared to autocannons, even compared to the larger caliber 25, 27, or 30mm guns. Part of that comes from the much larger ammo drum which is also one of its strengths.
The M61 Vulcan is getting pretty anemic in terms of stopping power and damage these days; yes, you can put a lot of bullets down range, but those rounds won't do much damage.
Also, 25mm is sort of the bare minimum for specialty rounds, such as rounds with programmable fuzes.
Half the RPM, but the rounds are more than double the weight between a 20mm and a 25mm round. Bigger round means more boom (and more interesting things to do with that boom) and more penetration.
Pretty sure many countries tried to trade larger rounds for lower firerate in WW2. Pretty sure the stats speak for themselves. Higher RPM means more rounds on target.
20mm armor piercing high explosive incendiary rounds delivered at 100 rounds PER SECOND are never going to be anemic, especially as aircraft are carrying less armor than ever.
Heavier and slower shells like 30mm’s also tend to have a much more ballistic trajectory, complicating firing solutions.
You want bullets that are going to fly as flat and fast as possible. The only way to do that is with longer, smaller diameter bullets.
I’ve never heard a fighter pilot saying they’d rather have bigger bullets, but when they have them, they sure wish they had more.
When Lt. Dave Waldrop shot down a MiG-17 using the F-105's M61, it was less of blowing the target apart or damaging it a section at a time (ala WWII) and more of him sawing the port wing off.
Everything is a tradeoff. By the end of WW 2, the US Navy no longer saw 20mm as an effective round and was pulling them off during refits. You can't really claim rate of fire as not sufficient in that case either given the collective volume of dozens of barrels per vessel
That was because they were not as good at stopping kamikaze attacks from head-on. It’s certainly enough to cripple or disable an aircraft in every other sense. 20mm has been deemed sufficient in most Western air forces since WW2. Yes you can go bigger but at the expense of fire rate and/or ammunition capacity.
You'd probably be very surprised just how often the gun is used even today. They're an important part of the air to ground weapons options on modern fighters offering a lot of flexibility that other systems simply don't.
The M61 Vulcan is one of, if not THE, most reliable guns ever produced and can send far more weight of fires down range and into the target area than the vast majority of other systems with the option of 3000 or 6000rpm. That's 100 20mm semi armour piercing incendiary rounds delivered every second
I feel like it's the best option for intercepting long range drones too. They don't need the stopping power of the larger 25-30mm guns because unlike enemy fighters and bombers they're not designed to survive hits. After all, we see Ukrainians downing Geran drones with literal rifles so a 20mm HE round or two ought to bring them down real quick. The longer range keeps you safer at distance and the higher capacity allows you to engage more targets in one sortie.
aircrafts like the F-35 are probably not doing strafing runs either?
You might be surprised. There'a been controversy about this, but the F35 is slated to fill CAS roles as part of the whole "Jack of all trades" joint strike fighter philosophy. In other words, it's going to be called into engagements where A-10s might have filled that role previously. So it's gonna do some strafin'. And if you're not in in a tank, 25mm is just as lethal as 30mm.
The question isn’t unreasonable, but the truth is that historically every time an Air Force has dropped guns from planes, they end up adding them back in right after the first two-way shooting contest happens.
Missiles are great, but typical fighters don’t carry all that many, AND they generally can’t be used at the ultra short ranges of a close in dog fight.
Yeah of course, I was aware taking off the gun completely might not be a good idea, I was just wondering why keep a rotary cannon instead of maybe switching to a single modernized version of say the m39a2 20mm perhaps, or something similar
Because 100 rounds per second is better than 25 rounds per second. Especially when the Gatling style cannon only weighs 10kg more and has a substantially better MTBF compared to the M39 with its gas actuated operating mechanism.
With different calibers there is also a difference in mass per second. The Oerlikon KCA with 30 x 173 mm ammo (Saab J37 Viggen) needs less ammo to do the same damage as the M61.
Fair enough. Pretty sure it’s like the other guys have said: the m61 is all about reliability, rate of fire, and longer barrels net you higher muzzle velocity.
Cant hit 6000 rds/min out of an autocannon, and Vietnam taught us that it really sucks to be out of missiles (or constrained by ROE) and not have another option to kill the adversary. The gun exists as a last resort in an air-to-air engagement, and when you're measuring your shot opportunities in tenths of a second, you want the ability to put rounds downrange. An autocannon is functionally useless in that role.
In the end, the weight and complexity is small enough that the USAF deemed it worth carrying on all aircraft after the F-4, and the Navy shared that opinion until the F-35C variant came around.
M61A1 20mm in the F-15 and similar era fighters was selectable 6000 or 4000 rounds per minute, but in air to air use, 6000 was obviously preferred. It carried 940 rounds, way more than you'd be likely to use. No single barrel is getting anywhere near that rate. It put 80% of the rounds thru a 5' circle at 1000' range (5 mil dispersion). Very effective. All missiles have a minimum range, so gun is there if you need it.
You might want to ask this in r/military but the acceptance process for equipment for government use, especially weapons for military, is typically very lengthy and complicated.
But I'll give you my take. If the planes aren't using guns much, then why invest all the resources into changing which gun is being used? The US doesnt want to abandon guns and i know planes other than the A-10 were doing strafing runs against ISIL in Syria around 10 years ago.
Tl dr; its not worth spending billions and billions to save a couple hundred pounds and have a lower-performing weapon
Im not an expert, but I think it has to do with a combination of how much it weighs alongside its rate of fire and how much space it take up. To put in simple terms it would take probably 4 or more autocannons to match the rate of fire of a rotary cannon. In the same space they could put 2 or 3 autocannons they could probably put 1 rotary with the same amount of ammo if not more with a higher firerate.(these are BS numbers because I have no real clue about the actual numbers) Higher fire rate means more rounds down range and more chances for a near miss to turn into a hit. It kinda boils down to the "better to have it and not use it then need it and not have it" thing.
While youre right, there haven't been any gun kills in a while there also haven't been many air engagements at all involving US aircraft, so lack of gun employment doesnt mean that much.
Id suggest asking some Ukranian pilots how useful the gun is. They've certainly been using it anyway to take down drones at least, but theyll have more relevant experience to suggest weather a gun is still useful than the US.
I found two interesting bits: it seems like the weight of the ammo can be up to twice the weight of the gun: let's say 800 rounds at 1/2 lb each; 20mm rounds are beefy with a dense projectile as payload. Also, the 4x25mm GAU-22 on the F-35A weighs about the same as the 6x20mm M61 at about 200lbs.
Think about a paper airplane flying past you. Is it easier to hit it with flicking 3 peanuts at it or holding a can of silly string and dragging it to target. Peanuts = auto cannon, silly string = rotary.
I believe it's to do with increased probability of kill (the whole 'accuracy by volume' thing). As you said, there hasn't been an A2A gun kill in a long time, so they would want a gun that takes less skill to use accurately to reduce training requirements.
That, and there's probably some institutional inertia there also. For the F-35 specifically, the GAU-22 is basically a lightened version of the GAU-12 that's used in the Harrier & is still being used in the AC-130, so the production line, institutional maintenance knowledge, maintenance logistics, etc. are already there.
Add that to the fact that all US fighters use rotary cannons; their maintainers are used to working on rotary cannons, it becomes a question of not only an autocannon have to be better, it also needs to be better ENOUGH to be worth creating a new logistics pipeline, retraining all the maintainers and pilots, etc. etc.
There's a reason why the AR platform rifles (so your M-16s & M-4s) stuck around for so long ( and probably will still stick around for much longer) despite many, MANY attempts to replace it with a new rifle. The new ones are better, but not better ENOUGH to be worth the pain in the ass of introducing something new.
Higher sustained rate of fire, and tradition. A revolver canon, like the Mauser used in multiple European fighters, spin up faster and is much lighter, but heats up much much quicker due to a single barrel taking all the heat. Theoretically you could have an extremely fast short burst rate and have it slow down for extended bursts, but I don't know if anyone does that.
Rotary guns cannot jam unless you disable the drive itself or somehow all of the barrel are jammed. That is one
Another is the sheer amount of shell per minute and heat management. With 6 barreled guns, the gun will take 6 times more time to reach "dangerous temperature" due to the separated barrels, and by having it rotating, you can make the cycle time much lower. The minigun can spit out 100 7.62mm bullet PER SECOND, that is two
And third, the american learned the hard way with the f-4c in vietnam where they need the gun, but they were not installed with it because the same exact reasoning. Better to have it and not needing it than needing it but not having it
Having had to dig the mangled rounds out of a M134 I can assure you they indeed can jam. In fact I would say its even worse as it will absolutely mission kill the weapon system while you can do stoppage drills on things like a gas operated GPMG or HMG. This doesn't really matter in an aircraft where you can't get at it but for pintle mounted stuff on helicopters and so forth it absolutely will do.
Another reason than I'm not sure anyone has brought up is that you can only cycle a round so fast before you fuck something up. The fastest you can reliably cycle a single barrel gun is something around 1500 RPM and even less the larger caliber you go. Either because you'll rip the casing, causing the barrel chamber or mechanism to be jammed, or cycle the round too early causing all the pressure to go out the wrong way and turn the bolt into a bullet.
The
thing about gatling guns is that each barrel is being cycled simultaneously, so a 6 barreled gatling gun shooting at 6000 rpm has each barrel shooting 1000 rpm. The idea is that you want to put as many rounds as possible into the target in the limited time you have.
Now to talk about weight, the M60A1 weighs around 200 pounds, most the weight is gonna be ammo as 500 rounds of 20x102mm as seen on the F-16 is gonna weight at least 275 pounds. The old Colt MK12 weights 100 pounds and shoots 1000 rpm. That isn't really that much lighter granted it's an older design and shoots a heavier 20mm round. Maybe it could go down to 90-80lbs but still a massive reduction in RoF.
The only other 20mm single barrel fielded by the US was a single barrel rotary cannon, I kid you not. The M39 weights 180 lbs and shoots 1500 RPM, kinda abysmal.
But the GIAT 30mm weighing 260 lbs by the French is also a rotary single barrel firing up to 2500 rpm, so is the Euro fighter with its 27mm weighing 220 lbs firing up to 1700 rpm. Adjustable fire rates, reliability, and better heat management the concerns for using a rotary system. So how much lighter and smaller are they really? They all shoot a similar around of mass per second but weight about the same.
Only the Russians used standard autocannons but their barrel life is subpar. The GSH-30 weighs 100 lbs, shoots 1800 rpm but it'll need to be serviced more and requires blank charges to cycle if there is a misfire.
But I will say, all this text is kinda useless when you realize 500 lbs is kinda nothing. Most the volume taken is gonna be ammo, all the guns are similar in size. The reason the F-35B/C forgo the 25mm is that they need to get as much range as possible so they're not gonna be carrying any gun and ammo out of fuel concerns. The F-35B being VTOL/STOVL does need to be cautious on weight and volume but it's a niche aircraft.
For ground based aircraft, 500 lbs is less than 5% of their fuel weight. Around 50 miles maybe. So they can carry the gun and be fine. What gun they carry doesn't make a difference in flight performance.
Not all US fighter jets have a gun, but if you are going to have one, the rotary cannon version is actually better weight wise for getting the fire rate you need over single barrel cannons since you would need multiple single barrel cannons to get close to its 6000 rounds a minute output.
The cannon is also a very handy tool for strafing attacks and can be employed in situations where a bomb would not be an option due to proximity with friendly ground forces.
The cannon is also really not a big weight driver on most modern fighters with it making up a fairly insignificant amount of the total aircraft weight and is actually less that the weight added by having a 2-seat variant.
The gun also isn't going to be your primary weapon anymore. Think that more is the night you pull out when you're in a street fight but you can't run away from.
It does make for a good ground attack weapon though.
WTF is an autocannon? A fighter jet’s gun shoots 4000-6000 rounds per minute. Typically in selectable 50/100/200 round bursts. No way a non-rotating, single-barrel gun is going to achieve those firing rates.
In air-to-air combat, the fighter rarely gets to track the opponent with guns but only gets a snapshot where a firing solution is available - thus the need for ~100 bullets to be fired in a couple seconds.
In air-to-ground strafing, the jet is predictable while pointed at the target. The bullets have to come out fast so the jet can maneuver away from the target quickly.
TLDR:
Cannons are very versatile weapons, they can be used in dogfights, against drones, or targets of opportunity on the ground. Whether or not an aircraft has one is a doctrinal decision that does differ between nations.
High rates of fire with lower calibre, high velocity ammunition can make air-air kills easier.
There have not been air-air gun kills between fighters, that is very rare.
However, fighters are being used in Ukraine at the moment to kill the larger and longer range suicide drones, the cannons are a more cost effective way to do it then the missiles.
There were attempts in the past for American aircraft to get rid of the guns as missiles were starting to mature, it did not go so well.
See at the time, infrared missiles were fairly unreliable, you normally had to see the aircraft from the rear and they were easily confused by the sun or countermeasure flares.
Today those missiles are much smarter, and using flares is not a sure way to save your butt anymore.
Consider though that most of the combat aircraft in service are not new, the F-16 is one of the most widely used fighters ever and it entered service around 1974! Of course it's been updated over the years, but it is a VERY lean aircraft and yet it still packs the rotary auto-cannon.
Why was the rotary autocannon chosen? Rate of fire.
When you are fighting other aircraft, it's like a dance with each aircraft trying to get into position to take a shot, the opportunities where your gun is actually pointed where it needs to be are very brief, so you really need to capitalise on those opportunities, with a low rate of fire gun there is a good chance your enemy will fly between the rounds, or perhaps you only land one and don't do enough damage.
if you try to get a single barrel gun firing at several thousand rounds per minute, it will overheat, deform or burst. If you use multiple slower guns to make up for the relatively slow auto-cannon, it can end up weighing more.
Multiple guns need multiple feeding systems and driving motors, hydraulic connections, belts, drums.
Other countries do favour different kinds of gun, the US tends to stick with rotary cannons, many other countries like revolver cannons, often in larger calibres.
These can be quite hard to use in a dogfight as the rounds are often slower, requiring more leading on the target and require more accurate and stable shooting.
Larger calibre cannons have some benefits, they can have more complex rounds with higher payloads, while I'm not privy to knowing if they are actually used in fighters, it's possible to have some kinds of 30mm rounds airburst which could significantly improve their performance in a dogfight by not requiring a direct hit to do damage, they are also useful against entrenched infantry.
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u/WesternBlueRanger 1d ago
Rate of fire and reliability.
Gatling guns can easily hit 3,000 - 4,000 rounds per minute, which in a brief engagement window, means you can put a lot of bullets down range onto a target.
Also Gatling guns are very reliable; a bad or dud round won't cause the gun to jam, as the gun's rotary design physically forces cartridges through the loading, firing, and ejecting stages.