Rate of fire/rounds per minute

[44 AMP]

There are 3 terms mentioned so far that relate to the number of rounds being fired. For two of them, RPM is used as an abbreviation, and you need to know the context.

Cyclic rate
This is the rate the mechanism cycles at. It is expressed in RPM. It is the rate the mechanism will run at if fed a continuous supply of ammunition, but it may not be (and usually isn't) the number of rounds fired if the gun were run continuously for a full minute, since most guns cannot run continuously for a full minute.

A belt fed gun could run continuously for a full minute, with enough belts linked together, something fed from a magazine cannot do that.

The actual number of rounds that can be fired in one minute is "rate of fire", and is also expressed as RPM, but that rate is less them the cyclic rate of the action due to practical considerations.

SO you have to understand the context when someone uses the term RPM. They can be talking about two different things.

Adding to the confusion is people being "conversationally sloppy" using rate of fire when they mean cyclic rate, the way people use engine and motor as interchangable terms in casual conversation when in technical terms they are quite different things.

Also mentioned was "sustained rate of fire" which is a much lower rate, it is the number of rounds per minute that the gun can fire, for long periods of time without overheating and excessive wear. It is something more important to artillery than small arms, generally.

 

[ballardw]

My comment was targeted at the AR and extreme rate of fire not the Metal Storm.

If you want to see an interesting (very hypothetical) discussion of the Metal Storm read John Ringo's "Hell's Faire" where a Metal Storm 105mm pack is used in the "anti-spaceship lander" role mounted on a modified M1 Abrams chassis. The Shiva gun is also entertaining.

 

[44 AMP]

Bun Bun rocks!

However, in those books the crews of the Metalstorm tanks got rather abused. In one scene a nuclear class detonation happens close just as they are firing and one crewmember asks 'what was that last bang??"

Ringo is my current favorite military SF writer.

Metalstorm is the ultimate muzzleloader. But the muzzle loading is done at the factory, not in the field. There is, literally, no action to cycle. Projectiles and powder charges (no cases or primers) are loaded one ahead of the other and can fill the entire barrel length (or nearly so), rounds in the barrel are fired sequentially using an electronic ignition system, and barrels are bundled together into "packs" becoming the ultimate "volley gun".

Not something very applicable to individual small arms, currently. Possible use as a crew served weapon, but not yet (if ever) superior to a belt fed machine gun. Once you get above that, you're into artillery and there, the concept has potential, (and some drawbacks).

To get back to the OP

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???

What controls the cyclic rate is the design of the arm. Springs, buffers rate reducers and sometimes accelerators, weight of the bolt, and other moving parts, and time required for the pressure to drop enough to allow extraction, all these and other factors are taken into consideration when they gun is designed. Also designed in is the desired cyclic rate for the intended use. Aircraft machineguns run at high rates because engagement time is very brief. Infantry machineguns run at lower rates, for better control and longer sustained firing.

The M60 machine gun is rated at 550-650 rpm, not 900.

What controls the number of rounds that can actually be fired in one minute is the available ammo supply ready to feed into the chamber. Belt fed guns can run as long as the belt, magazine fed run until the magazine is empty, then they stop until another loaded magazine is inserted and then firing can resume. This takes time, and that time not firing means that the number of rounds actually fired in one minute is less than the cyclic rate of the action.

 

[ballardw]

Bun Bun rocks!

However, in those books the crews of the Metalstorm tanks got rather abused. In one scene a nuclear class detonation happens close just as they are firing and one crewmember asks 'what was that last bang??"

Ringo is my current favorite military SF writer.

I had hoped that TXAZ would find that out in context.

There's a certain charm in that. The question is should "anti-matter" detonation be described as "nuclear".

And remember, "Don't let rednecks play with anti-matter!" (Same book for those confused.)

 

[44 AMP]

while in the class of nuclear detonations energy, antimatter would not be a nuclear detonation, because its neither fission nor fusion.

*not a physicist don't play one on TV*

do have 30+ years as a certified fissile material handler, though...

 

[JohnKSa]

SO you have to understand the context when someone uses the term RPM.

Indeed. Fortunately the OP's context is quite clear--the question is obviously about cyclic rate.

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

It depends on the type of action, to begin with.

The cyclic rate of a gas-operated gun can be increased by allowing more gas into the action. That's assuming the action is designed to handle it.

In a recoil operated gun, lightening the recoiling mass will generally increase the cyclic rate, depending on how the locking mechanism is set up. And, again, assuming the action is designed to handle the extra energy of the recoiling mass.

I think asking about one specific gun might net some more useful responses. I think asking the general question opens things up so wide that it's hard to give a good answer.

 

[44 AMP]

It depends on the type of action, to begin with.

Often it ends with the type of action, as well.

Sometimes, increasing the gas doesn't result in any appreciable change to the cycling rate it just makes the parts slam harder. Yes its because they are moving faster but the result is dependent on the specific action particulars.

Adjustable gas systems on some belt fed guns are there to provide more gas to keep the action running when it becomes sluggish due to the build up of heat, firing residue, loss of lube or foreign matter found in combat conditions.

Other "adustable" systems are not firing point adjustable, requiring changes in buffers and/ or springs or other parts to change the firing rate.

How much can be changed and how it is done is entirely dependent on the design of the action. There's no free lunch.

 

[tango1niner]

In the very early 70's I was trained as a M-60 gunner to shoot 3-5 round bursts. We shot at 55 gal. drums 1100 meters distant. Every 5th round a tracer made it easy to walk your shots to where you needed them. I will add that while the M-60 was my assigned weapon I never fired it in anger and was happy about that.

 

[Willie Lowman]

There have been a few open bolt submachineguns made where weight can be added or removed from the bolt to change the rate of fire.

 

[44 AMP]

There have been a few open bolt submachineguns made where weight can be added or removed from the bolt to change the rate of fire.

Which ones would those be??

and, are you talking swapping a bolt for a heavier one, or using the regular set up and adding or removing weight somewhere?

 

[101combatvet]

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???

900 rounds a minute? Usually, it's the machingunner's finger that controls the rate of fire.

 

[Willie Lowman]

Which ones would those be??

The Czech ZK-383 and the Stemple take down gun come to mind. Both had weights you could add or remove from the bolt to change the rate of fire.

https://www.youtube.com/watch?v=MlFdhAK5c7Q

 

[Drm50]

The weight of bolt and the length of recoil stroke. The rate of fire is not affected by the trigger. Some MGs can up RPM by putting spacers in recoil buffer. As long as complete cycle can be made without metal to metal contact. There is a limit on the rounds per minute on any given conventional gun. There are many ways to slow them down.

 

[44 AMP]

The rate of fire is not affected by the trigger.

The cyclic rate of the action is not affected by the trigger, (or the gunner's trigger finger). RPM (rounds per minute) is the term used for the cyclic rate.

The rate of fire, the actual amount of ammo that can be fired in one minute, is ALSO expressed as RPM, but is subject to the gunner's finger, and the amount of ammo that can be fed into the chamber.

So you have to be aware of the context to understand the differences.

A box magazine fed machine gun has an actual rate of fire much lower than the cyclic rate of the action. A belt fed can potentially run at the action's cyclic rate, IF you have enough belts linked together and can keep them feeding smoothly.

However, air cooled types are still subject to heat build up during continuous fire which at some point will render the weapon inoperable.