[M. Eversberg II]

[R D Moore]

Pre 19th Century it shall be.

Glen,
Thanks for the pic. That bird is a real : "can of whup a--!"

[Glen A Cleeton]

[David Jenkins]

All belt fed machine guns are open bolt, this means when you fire, the bolt slams forward. The firing pin is fixed in the bolt. This dosen't do wonders for accuracy there tends to be a spread, but this can be useful. When mounted on a tripod and used in the indirect fire role (fire up in the air) this spread is known as the beaten zone (oval shaped), very similar to a hundred longbowmen raining arrows down on you.

Magazine fed weapons can be either open or closed bolt, rifles are almost always closed bolt, while the cheaper submachine guns are usually open bolt (because you don't need a separate moving firing pin).

The GPMG & M60 are both belt fed (open bolt), but the Bren gun is mag fed and closed bolt. In the 1980s the NZ army had all three. If you aimed at a small tree the GPMG & M60 will shred it, the Bren gun if moved sideways will saw the tree down like a chainsaw.

Because of the heating and recoil issues belt fed are built heavy, plus you need a spare barrel or two (unless water cooled = more weight) and heaps of ammo. But have a greater sustained rate of fire.

[Christopher H]

[Stephanie Maks]

[Darryl Aoki]

A couple of drawbacks to the fabric belts used in several medium MG designs were:
1. There was no positive locating/locking feature for rounds. Vickers gun belts had tabs to indicate the proper insertion length for a cartridge, but there wasn't anything to keep the rounds from moving around or falling out, which could cause the gun to malfunction.
2. Fabric swells when wet, which had the effect of distorting the belt and increasing the likelihood of jamming.
Disintegrating-link belts don't have either problem, though, and I believe that that's the standard design of ammo belt in use today.

And then there's the odd little rigid belt that the Hotchkiss gun (and its Italian and Japanese descendants) fired, which makes me think of typewriters for some reason, but oh well.

[Bryce Felperin]

[Bryce Felperin]

[Jean Thibodeau]

[Stephanie Maks]

I wonder if there might be some confusion over firing from an open/closed bolt due to the actual way one controls some of these weapons. If I remember right looking at a relatively modern .50cal (I think it was a Browning) there was the bit you press with your thumb and the bit you pull with the finger(s). One of them let the bolt close and the other one released the firing pin. You need to do both at once to get full auto fire. The fact that you could make it fire by releasing the bolt did not mean it fired from an open bolt; internally the firing pin mechanism was still operating separately, after the bolt closed and locked.

My understanding of the term "firing from an open bolt" was that there was no separation between the closing of the bolt and the firing of the cartridge - the firing pin was more or less fixed to the bolt itself. Firing from a closed bolt meant that the firing pin / hammer / etc were independant of the bolt and the firing pin would not be released until after the bolt was closed and locked. Put it another way, if you can close and lock the bolt without firing, then the gun fires from a closed bolt.

IIRC there was actually a Winchester .22cal single-shot rifle which fired from an open bolt. When the receiver was opened, this 'cocked' the mechanism, but left the bolt open so you could drop the cartridge in. Pulling the trigger released the bolt and firing pin on the cartridge which fired the gun.

Apologies if my terminology is rusty... I studied gunsmithing about 10 years ago but haven't done anything with it since then.

-Stephanie

[Jean Thibodeau]

Well, some submachineguns do have the firing pin machined into the face of the bolt but some full-auto weapons still use a separate firing pin even if they do fire from the open bolt position.

So many different weapon designs that almost every possible mechanism has been used, so one can't generalize for the whole class.

One reason for firing from an open bolt is mostly cooling and avoiding cook off of a round in the chamber of an overheated weapon and going unstoppable until the ammunition supply becomes exhausted !

Some mechanisms can be easily modified in theory from open bolt to closed bolt firing since all the parts are basically there and need only some slight design modifications to permit closed bolt firing by controlling the fall of the firing pin or a hammer strike to the firing pin separately from the bolt.

Some designs use the forward momentum to damp down on recoil forces and are able to use a lighter recoil spring since the cartridge is fired before the bolt has come to rest: The force of the bolt still moving forward counteracting the backward force of the cartridge wanting to eject. This makes for better recoil control and takes some strain of the mechanism and is a question of " timing " the ignition precisely.

Not a gunsmith or an expert but I did have a period where my focus was more on modern weaponry than currently.
( Now if I drift into explaining the functioning of a " Phaser " or " Photon Torpedoes " you will know I have gone off the deep end or have been typing and drinking. ).

[Gavin Kisebach]

[Hunter B.]

[Gavin Kisebach]

Well I do apologize if memory has failed me, but I was told this from Basic training through the day I walked out the door by drill SGTs, squad leaders and platoon daddies, and my own experiences backed it up. Whenever we got "clever" and switched out, the results were poor. If this is a military myth then mia culpa for not double checking.

IIRC the M855 was for the SAW and M193 was for the M4. I know they had different grain weights and corresponding chamber pressures. One had green tip and the other was bare, and I think the green tips came on belts. Again; I could be wrong but i do know that there are at least half a dozen 5.56 rounds used by the US Army.


[edit] and you're correct about the 203 vs mk-19, the rounds don't look anything like eachother and the 19 round would probably mutilate a 203, if it would een seat in the tube.

[JE Sarge]

Reservist since 1987 here, I'll input my .02.

Some belt-fed firearms are perfect if maintained properly. I found that the M2 and M240 (M60) are great weapons if the operator knows the nuiances of the weapon. The M249 (SAW) and Mk19 are really fickle and is apt to give you problems at any time - there is nothing that you can do as a gunner to prevent this at length, although you can reduce the overall chance of failure (IE, using liquid Crisco instead of .mil lubricants).

As far as belt-fed reliability vs. magazine fed, I would have to state that magazine fed is superior as far as short bursts of auto or semi fire and reloading is simple; jams are also exceptionally easy to clear under stress. Belt-fed gives a better sustained burst, but gets hot quickly and is a bear to reload in a combat scenario; jams are a nightmare to clear (when your Mk19 jams, you literally have to bang on the HE round with a screwdriver or pinion rod to jar them loose at times). I've reloaded a M2 and Mk19 on a moving guntruck, and I am here to tell you it is damn near impossible. Either has its benefit in what your mission is. I'd rather have an M2 or Mk19 on a truck regardless of them being a pain in the rear, but rather have a M4 than an M249 in a MOUT situation because I don't want a belt to get snagged and break or cause a jam.

SAW ammo is linked one way currently in theater (at least in 2005-2006 during my last tour). It comes in a 200rd belt of a ratio of 4 M855 AP (green tip) rounds to 1 M856 tracer round. I've seen belts of M193 (plain old copper jacket) used on the range before, but more often that not, they just use the combat load so you can see where to adjust your fire without having to use the sights.

Other input: No, you cannot use a Mk19 round in a M203. The length of the cartridge is longer on the Mk19 round. It will fit into the breach of the a M203, but the slide will not lock closed. It's like trying to make a 10mm round fit into a .40 caliber weapon. Since the firing pin of the M203 will not release unless the breach is closed, it cannot be fired unless there is something seriously wrong with the M203 internal safety mechanism.

Hope I shead some light on this for you...

[Hunter B.]

[Bryce Felperin]

Okay, now we're sounding like a gun board! Lots of specifications and talk on which round is better, what weapon is more reliable and what one prefers.

Knew this would happen. Next up, arguments on which is better between AK's and which M4 clone is the best!

:-(

[JE Sarge]

This is a matter of personal opinion and experience, but:

The best US assembled AK is made by Vector Arms and the best M4 would be the Rock River Arms LAR-15 TLE. I own both and never have given me a problem.

Next question?

[Gavin Kisebach]