Machine gun rate of fire, in armies [Archive] - Glock Talk

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ithaca_deerslayer
04-16-2010, 09:45
What is generally seen as the ideal rate of fire for a machine gun?

I've read that in WWII, the US Browning .30 cal was about 550 rpm. And the German MG 42 was about 1200 rpm.

That seems a big difference. What rpm would be ideal, and why?

Stuff I've thought of on my own:
-- high rpm goes through ammo faster
-- high rpm maybe heats up barrel too fast
-- 550 rpm seems pretty fast to me, count 1,2,3...10 as fast as you can, and 550 would be faster.


Also, how does a machine gun chamber a round without squishing the belt into the chamber?

Batesmotel
04-16-2010, 16:56
Also, how does a machine gun chamber a round without squishing the belt into the chamber?

2 methods were used for belt fed guns.

#1 for the older cloth belts a claw on the bolt grabs the rim as the bolt is going to the rear. As the round clears the belt it drops down below the cloth and then the bolt runs it forward into the chamber.

#2 for the newer guns they use a disintegrating belt. The links in the belt are metal clips that are held together by the cartridge case. they only cover the top and sides of the case leaving one side (placed down on the gun) uncovered. When the bolt goes forward it is slightly lower than the round, catches it and strips the round out of the links via the uncovered side and one link falls out. There was a good animation on youtube showing both methods.

A M2 browning can shoot as slow as 400 rounds per minute and an M134 Minigun shoots 6000 rounds per minute.

ithaca_deerslayer
04-19-2010, 07:30
Thinks for the info about the belts. I didn't realize the round was first being extracted from the cloth belt.

With the metal links, what happens to those links? How do they get cleaned out of of the action area so they don't cause a jam?

Batesmotel
04-19-2010, 07:46
Some guns like the M-60 have basically two ejection ports on the right side. One on top of the other. Links come out of the top and the spent brass comes out of the bottom. Some guns eject links out the side and brass out the bottom. Check out you tube and you will see how it works.

1gewehr
04-19-2010, 09:45
What is generally seen as the ideal rate of fire for a machine gun?

I've read that in WWII, the US Browning .30 cal was about 550 rpm. And the German MG 42 was about 1200 rpm.

That seems a big difference. What rpm would be ideal, and why?


There is no one "ideal" rate of fire. It depends upon how you intend to use the gun and what it's intended role is. There is also a major difference between a supported machine gun and a shoulder-fired automatic weapon.

One model is to draw a line from the muzzle which represents a barrier to opposing troops. Fairly continuous fire (6-9 round bursts) at a low cyclic rate would prevent the opposition from crossing that line. Picture a WWI trench line with machine guns at each end firing so that their fires cross. Obviously, a low rate of fire is sufficient to prevent attacking troops from getting across, while conserving ammo and keeping the gun from overheating. American troops were taught to alternate fires, making this even more effective.

Another model is like a long-range shotgun. This is the "beaten-zone" concept. If you see a group of troops at a distance, you fire a 10-12rd burst at them. The natural vibration of the gun will create a certain amount of dispersal in where the bullets impact. This is called the "beaten zone". In this case, a faster rate of fire means that the bullets arrive in a similar manner as buckshot. This creates greater casualties in the opposition. If firing at a point target (bunker), the higher rate of fire and smaller beaten zone means a greater hit probability.

For shoulder-fired weapons, a lower rate of fire is generally preferable. Sub machineguns are most effective when the shooter can easily choose how many rounds get fired by trigger control. The world's best combat sub machineguns have firing rates from 400-600 rounds per minute. That is slow enough that a single shot can be easily fired by a trained person and multiple rounds can be easily kept on target without being thrown around by recoil.

But even here, one theory is that a high-enough rate of fire allows multiple shots to exit the bore before it is moved off-target by the recoil. But this is usually proposed for lower-power cartridges like 5.45 and 5.56mm. In which case, why not use a round more likely to cause the target to go down and just fire one round?

pennlineman
04-19-2010, 11:20
Its been a while since I've worked with a machinegun. Almost 20 years. The rates of fire will vary from weapons systems.

The M-60 for instance Had three rates of fire.

Sustained- 100 rnds per minute. Barrel change every 5 minutes.
Rapid- 200 rnds per minute. Barrel change every 2 minutes.
Cyclic- 550 rnds per minute. Barrel change every minute.

The role of a machinegun varies greatly depending on the mission at hand. For instance a M-60 in the hand of an advancing infantry man or mounted on a vehicle would be different than one set up on a tripod in a defensive posture.

In all cases the main purpose in to deliver a high volume of accurate fire upon the enemy. When a machine gun starts, people have a tendency to take cover. So supressive fire is a big role. This allows the riflemen and those with other weapons such as grenade launchers to move to a postion to destroy the enemy. In some cases it can keep them pinned down until additional support such as air or artilery if you have that luxery. For those who refuse to play be the rules and keep moving, a good gunner will make them wish they had not.

With regards to the ideal rate of fire, the least amount you can use and still accomplish your mission would be the answer. Ammo conservation and less barrel changes. A gunner who gets excited and wastes all all of his ammo too quickly is of little use with a 23 pound club.

A tripod mounted gun in a defensive position can cover likely avenues of approach or areas that can be used as cover such as a stone wall. By using a range card and the tripod and traverse and elevation device. So even if it is dark or the area is obscured by smoke, the gunner can still effectively engage the pre-determined targets. This is where a gunner is often given an order involving a rate of fire. For instance, he may be given an order to fire at target X for one minute at the rapid rate of fire. So he is being told to fire about 200 rnds within a minute at the target. A target such as a hedge row, he would traverse and search with the T&E as he engages the target to cover as much as he can.

A book could be written on machinegun characteristics and tactics. Tactics change and I'm somewhat dated.

Most modern machine guns are top feeders. As the bolt goes forward it strips a round from the metalic links and cartridge guides press the cartridge down towards the chamber. As the bolt is being driven to the rear after firing it interacts with feed pawls that will bring the next round in line with the barrel, at the same time pushing the old links out to the right.

ithaca_deerslayer
04-20-2010, 07:41
1 gewehr, thanks for that post.

Lots of great info that I hadn't known before. I like to read WWII books, but I never saw that stuff discussed. Guess I got to find some better books :)

ithaca_deerslayer
04-20-2010, 07:48
The M-60 for instance Had three rates of fire.

Sustained- 100 rnds per minute. Barrel change every 5 minutes.
Rapid- 200 rnds per minute. Barrel change every 2 minutes.
Cyclic- 550 rnds per minute. Barrel change every minute.

Lots of great information in your post, too! Thanks :)

About the barrel changes, how long does it take to change the barrel?

I would have thought that when the barrel gets heated up enough that it needs a change, that the threads would be virtually like welded together and it wouldn't budge? But maybe that's not what happens.

And after you change a barrel, do you just let it cool for 5 minutes and then screw it back on, while another barrel is doing the firing? Do you try to douse it in water? How many barrels do you use, just 2?

1gewehr
04-20-2010, 08:53
About the barrel changes, how long does it take to change the barrel?

I would have thought that when the barrel gets heated up enough that it needs a change, that the threads would be virtually like welded together and it wouldn't budge? But maybe that's not what happens.

And after you change a barrel, do you just let it cool for 5 minutes and then screw it back on, while another barrel is doing the firing? Do you try to douse it in water? How many barrels do you use, just 2?

Most modern machine guns don't have barrels that thread into the receiver. They usually have a rotating cam that locks the barrel into place when you slide it into the trunnion. Some guns have the cam attached to an insulated handle so that you can easily carry the hot barrel away. There are other mechanisms, but they all allow the barrel to be removed without unscrewing.

Typically, changing a barrel on an M240 takes less than six seconds. Changing one on an MG42 is about three seconds. There are videos on YouTube showing this.
http://www.youtube.com/watch?v=dWD_N6v2tkU
http://www.youtube.com/watch?v=qf5oRuRoQEE

Most armies just issue two barrels per gun. When not firing, they cool down pretty quickly. Swapping between two barrels allows a lot of firing.

ithaca_deerslayer
04-20-2010, 11:16
Thanks for the youtube links. I didn't realize it was so quick to change a barrel :wow:

Here's a short video I found there with the MG42 firing. Man, that sends a chill up my spine just imagining American soldiers hearing that and trying to dive to the ground for a place to hide.

http://www.youtube.com/watch?v=AwW31u6wYvE&feature=related

Batesmotel
04-20-2010, 13:32
Imagine the Germans trying to hide from the Browning M2. The penetration of the .50 is terrifying. Gouring said that if his planes had been armed with the Browning .50 he would have won the Battle of Britain. A Spitfire with 8 Brownings could shred a ME109.

1gewehr
04-21-2010, 07:57
A Spitfire with 8 Brownings could shred a ME109.

Except that a Spitfire had eight .303 Brownings, not .50s. And only 300rds per gun. Needless to say, pilots were taught to keep the finger off the trigger unless they had a good shot, and to keep bursts short. The Brownings had a rate of fire of about 800rpm each, giving a total weight of 107 rds/sec.

The Bf 109E had 2 8mm MG-17s and 2 20mm MG-FF. It also carried a much more limited ammo supply, only about 10 seconds total. The 8mm guns had a rate of fire of about 1000rds/min, the 20mm about 300rds/min. But the 20mm shells were explosive and a single hit was usually crippling.