Rate of fire/rounds per minute

[PolarFBear]

Every gun has a rate of fire, battle ships 2 shots a minute; M-60, 900 rounds a minute. What controls the rate of fire on an automatic weapon, bullet weight, recoil spring tension???

[ss1/G8RFAN]

Physics. You are converting chemical energy to mechanical motion which involves inertial energy of mass, (bolt, gas piston if applicable, recipricating parts), stored energy, springs, friction, etc. These are all tuned to the application needed for the weapon and desired cyclic rate. Ammunition is generally a parameter constant in design stages to keep reliability and functionality.

[Jim Watson]

That goes very far into the overall mechanical design, not as simple as just ammo or springs. Frex the .50 Browning ground gun is listed at 800 rpm, but there is an aircraft model for putting more lead on a fast moving airplane at 1200 rpm.

[44 AMP]

What controls the rate of fire on an automatic weapon, bullet weight, recoil spring tension???

The controlling factor is the operator /gun crew.

Understand that there are two numbers involved and they are not identical for hand held or crew served weapons, and usually not identical for weapons in fixed mountings (such as aircraft).

Look up a given machinegun in the books and you will find a rate listed, this is the cyclic rate of the gun. It is the mechanical rate at which the action cycles, expressed in rounds per minute (rpm). This is primarily determined by design factors, and is usually expressed as a range (550-600rpm for example), and additional factors can play a part, such as the condition of the springs, the specific ammo being fired, etc.

The cyclic rate is the number that engineers say they gun will run at. It is also the number most often used by people who don't know what they are talking about, and who think the gun actually shoots that fast.

They do not shoot that fast.

The other number is the important one for most uses and its usually called "rate of fire" (not cyclic rate), and it is the rate that the gun can be fired in the real world. IT is always lower than the cyclic rate because it includes the time needed to actually feed ammo into the gun. Changing magzines, feeding fresh belts, etc. It is also expressed in RPM. Its not usually found in the gun specifications.

And then there is a third number found in military user manuals, which is "sustained rate of fire" and this number is lower yet. IT is a rate number in RPM which takes into account the stress, wear, and heat of rapid fire, and intended to be a rate at which the gun may be fired "continously" without breaking down or burning out the barrel. Most often used with artillery but it has small arms applications as well.

For example say you have a 105mm howitzer and the book says max rate of fire is 17 rpm. A really good gun crew might be able to do 20rpm for brief periods, most will probably do less. And. doing so will wear out the gun tube in short order (significant shortening of its service life). We do that in emergencies. Regular firing rate would be 5-6rpm, which preserves the life of the gun tube.

Say the book says the cyclic rate of the M16 is 700-900rpm. That is the rate the mechanism cycles, not the rate at which you can shoot it. Lets just take the low end for example, 700rpm.

Now, take your M16, and have 23 loaded 30 rnd mags (690 rnds) stacked up ready and begin shooting. Brother, if you can fire them all out in 60 seconds, I'll buy your lunch! (you buy the new barrel for your M16 )

The same sort of thing applies even to belt fed weapons. Belts only hold a certain number of rounds. Usually 100 rnds for infantry guns, so while the gun might run at 600rpm, at the end of every belt, you have to stop, open the feed cover and insert a new belt, then close the cover, and possibly cycle the action to get the round into feeding position This takes a little bit of time, time when the gun is not firing. So, actually reaching the cyclic rate in real rounds fired in one minute is problematic and very rarely done.

Fixed guns, like in fighter aircraft, with high rates of fire (9-1200rpm) don't make the actual 1200 rnds fired in one minute, usually because they don't have 1200 rounds of ammo storage capacity, a matter of space and weight,

Our famous fighter planes in WWII with 4,6, or even 8 .50 cal guns in the wings carried at most 450-500rnds per gun and some only between 200 and 300.

So, don't confuse cyclic rate with how many rounds the gun can actually fire in one minute.

Semi autos also have a cyclic rate. Lower than most machine guns, usually, but not a lot lower than infantry MGs. Its the rate the action cycles at, and of course is much, much higher than the rate at which a semi auto can be fired.

To summarize, cyclic rate is the rate the mechanism functions at, rate of fire is the rate (rpm) that the user can operate the gun at. NOT the same thing.

[Jim Watson]

Regular firing rate would be 5-6rpm, which preserves the life of the gun tube.

Literary reference: A steady six rounds per minute which saves barrels and breaks armies. S.M. Stirling.

I think the cyclic rate of the original 1917 Browning was only around 450 rpm.
But Mr Browning sat down behind his second demonstration model and held the trigger down for 46 minutes. Certainly somebody linking belts for him for over 20,000 rounds. He said he wanted to shoot for an hour but that was all the ammo they had left after shooting a 20000 round burst the day before on the first sample gun.

[ballardw]

Very early Maxim machine guns weren't even close to fixed rate

This first model was very different to Maxim's production weapon: the heart of the mechanism was a crank resembling that of a piston engine in the rear of the weapon that rotated completely as the bolt cycled, requiring a very distinctive bulge to contain it. This version also had a pointer-operated fire regulator which allowed it to fire at any rate from 1 rpm to 600 rpm.

From, among others, https://guns.fandom.com/wiki/Maxim_gun

IIRC part of the adjustable rate of fire in the early guns for trials was because the militaries of the time had no idea what an "ideal" rate might be. Remember this is the same time that more than a few magazine fed bolt action rifles had magazine cutoffs with the intent that soldiers "wouldn't waste ammo" firing it too quickly and were supposed to continue to single load rounds.

[44 AMP]

Literary reference: A steady six rounds per minute which saves barrels and breaks armies. S.M. Stirling.

Messr Raj would approve!

With the notable exception of the MG42, up through WWII the majority of infantry machine guns had cyclic rates in the 4-600 rpm range. After WW I aircraft guns were made with higher rates of fire. Browning infantry guns ran about 450-550 rpm and ran, and ran, and ran. The standard joke in armorer's circles was "What is the number 1 reason a Browning MG stops firing?"
"It runs out of ammo!"

One thing underappreciated by people who have not shot machine guns is that recoil is cumulative, and the faster the cyclic rate, the greater the effect. Not too bad when the gun is mounted on something, and even a tripod goes a long way to keeping the gun on target, but when firing from a bipod or from the shoulder with an automatic rifle of .30 caliber, you get moved around a bit...

IF you get a chance, find a video of an M2HB firing from a tripod and watch the front leg. It often...hops a bit.

The receiver weighs 84lbs the barrel 28 or so, the tripod 65, and each round of ammo weighs about a quarter pound, and then the links weigh a bit, too.

Gives you some idea of the power of the gun's recoil, nearly bouncing all that weight off the ground...

[Jim Watson]

When Pawn Stars was looking at the half track with .50 quad mount and Corey got to shoot the guns, I noticed that one of them was not firing. The British supposedly used them on MGBs and said the reason for a quad mount of .5 Brownings was so you would normally have one gun to shoot.

[44 AMP]

The British say a lot of things, some true, others, not so much.

I've read British reviewers works on lots of things, and the one thing they all seem to have in common is that if its not British, its flawed in some way.

WWII US fighter planes were described as having cockpits like "executive offices" (large) and complain about all the "wasted space". And, our flight instruments are all in the "wrong" places....

they examined a captured Tiger tank, and concluded how difficult it would be to operate, due to the cramped crew spaces.

German crewman felt otherwise, one driver said how he loved the amount of space in the Tiger, there was actually enough room for him to sleep in the tank, something none of the earlier tanks had...

Its all point of view, I guess....

If a quad .50 isn't firing all 4 guns (and is set to fire all 4 guns) then something is broken and needs fixing.

[Nanuk]

44 amp, close. The M-16 has a sustained rate of fire of 12-15 rounds a minute. That is how many you can fire thru it in a long term to prevent over heating etc.

[dyl]

44 amp, close. The M-16 has a sustained rate of fire of 12-15 rounds a minute.

Wow that seems really slow for an infantry rifle. Not doubting the number, but in real life if someone needs to fire their rifle you can bet it's going to be faster than that for a short while. That's about the speed indoor pistol ranges wish folks would shoot at

[44 AMP]

12 rounds per minute is 5 seconds per shot. 15 rounds is 4 seconds per shot. This is a rate of fire that can be managed with manually operated repeaters, and I expect some skilled folks could manage it with a single shot breechloader.

Sustained rate of fire is just that, an arbitrarily chosen low rate of fire that can be sustained for minute after minute, until the mission requirement ends without overheating and wearing out the weapon. It is something normally used for artillery barrages and such things, where a steady slow rate of fire gets the job done.

And the military, being the military and having a military passion for having stndards has Sustained Fire rates for small arms, as well as the big guns. Very, very rarely used in small arms during combat. And, during combat, sometimes the sustained rate of fire for the big guns gets tossed aside, as well.

[Nanuk]

dyl, as 44 amp states is basically means the rifle can fire at that rate forever.

[hounddog409]

You're forgetting the reload. As does most when discussing RPM.

600 rpm is only factual if you have 600 rounds available without the need to reload

[TXAZ]

ss1 in Post #2 nailed it, it’s pure physics.
I believe Metal Storm had a max rate of 1 million rounds per minute but that never hit production (probably a good thing at current .30 cal prices.)

But some anti gunners have said on TV (so it must be true) that ARs can fire 30 rounds per second / 1800 rounds per minute. I’d like to see the barrel after 1 minute on that one.

[ballardw]

Originally Posted by TXAZ

ss1 in Post #2 nailed it, it’s pure physics.
I believe Metal Storm had a max rate of 1 million rounds per minute but that never hit production (probably a good thing at current .30 cal prices.)

But some anti gunners have said on TV (so it must be true) that ARs can fire 30 rounds per second / 1800 rounds per minute. I’d like to see the barrel after 1 minute on that one.

Suspect the gas tube would be an issue before the barrel. I saw a 100 round dump from a Beta C-Mag in a fully automatic M-16/AR platform that had the gas tube glowing pretty bright.

[tdrizzle]

Weren't M60 gunners taught to say to themselves 'fire a burst of six' each time they pulled the trigger, for both ammo conservation and cooling?