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Old April 1, 2021, 01:34 PM   #4
44 AMP
Join Date: March 11, 2006
Location: Upper US
Posts: 23,637
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.
All else being equal (and it almost never is) bigger bullets tend to work better.
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