What, exactly, does this mean? What is the mechanical reason for a variable rate-of-fire in a delayed-blowback weapon like the MG42?
CYCLIC RATE OFFIRE.- The cyclic rate of fire is the maximum rate at which a weapon will fire in automatic operation, stated in rounds per minute (rpm).
I’m not sure what you’re really asking…
As far as a variable rate of fire in the MG-42, it used a standard bolt head, and a lightweight bolt head that would increase the rate of fire by about 300 rpm. Normally that would be used for anti-aircraft use. Then as today, for anti-air, you want to put as much in the air in as short as time possible. Again, is that what you are asking?
As far as a variable rate of fire in the MG-42, it used a standard bolt head, and a lightweight bolt head that would increase the rate of fire by about 300 rpm. Normally that would be used for anti-aircraft use. Then as today, for anti-air, you want to put as much in the air in as short as time possible. Again, is that what you are asking?
The “cyclic” rate of fire is an automatic weapon’s rate of fire, calculated without taking into account the need to reload it or let the barrel cool or anything like that. If a weapon launches 10 bullets per second, its cyclic rate is 600 rpm, even if it only accepts 20 round magazines.
Sometimes, spec sheets will report an “automatic” rate of fire, which is how many bullets a soldier could be expected to shoot with the thing in a minute. So a belt-fed weapon which cycles at 600 rpm might have an “automatic” rate of fire of 300 rpm, while a weapon cycling at the same speed, but fed by little box magazines, might have be reduced to 80 rpm in practice.
And yes, I do believe this is a misuse of the word “automatic” - it is no more or less related to autofire than the cyclic rate. I would have called the cyclic ROF the “calculated” or “theoretical” rate, and the automatic ROF the “practical” rate. But I haven’t seen the goofy “automatic rate of fire” terminology used in a while.
I am probably over-answering your questions here, but what the heck. The reason for a variable rate of fire is pretty much what Turbo Dog said - higher rates of fire are better for anti-aircraft work and lower rates are better for slow sweeping of ground targets. I believe John Browning’s Automatic Rifle had two rates of fire but I don’t think the higher was for AA work.
As for how it’s done mechanically, I don’t really know much about delayed blowbacks. I suspect an adjustment to part of the system does the trick. With a straight blowback weapon like the Uzi, a parts change is required. I can’t remember if it’s the Uzi or the Mini Uzi, but a heavier bolt (of tungsten) can be substituted to bring the rate of fire down to a fearsome 750 rpm from the terrifying standard rate of 900 rpm (Micro Uzi users have to be satisfied with 1200).
The cyclic rate of fire depends on three things:
A) How heavy the moving parts (bolt) inside the gun are.
The reason this is important is that the heavier the bolt is, the harder it will be for the recoil of the outgoing bullet to push it back. Lots of inertia = slow movement.
B) How strong the spring is that move the bolt back into position after it’s been “blown back”. Obviously, stronger spring = higher ROF. Of course, you can’t keep making the spring stronger forever, because eventually it’ll prevent the bolt from blowing back far enough to grab the next cartridge off the top of the magazine.
C) Other misc engineering factors, like how fast cartridges
can be slammed in and out of the chamber without jamming, friction, etc, etc…
As an aside, I’ve fired a micro Uzi. They’re not kidding when they say 1200 rounds/min. The magazine holds 32. You pull the trigger and it’s like “BRRRRT!” And that’s it! 32 rounds gone in what feels like less than a second. Crazy.
-Ben
Thanks, Boris, that answers my question nicely! I thought that the rate of fire ‘cycled’ within a single burst for some mechanical reason. I kept looking at the mechanism, and couldn’t think of any reason why that would be the case. Misunderstanding terminology on my part.