Heavy Machine Gun

[Uncle Bob]

The XM109 stretches the concept of "soldier carred", as it is really crew-served. The recoil is brutal, much worse than the .50 BMG version.

The OICW (XM29, XM25) is now 25mm, using the same warheads as the OCSW (XM307) in a low veloicity cartridge. Plus an APERS flechette load that will make up for the loss of the 5.56mm component. But the low muzzle velocity makes "rifle" misleading.
Still on track for 2008, maybe sooner with RFI.

ATK's XM25 page

 

[Uncle Bob]

Automatic Rifle: full auto anti-personel weapon, usually with bipod. Usually with neither a large ammo feed or the ability to dissipate the heat of sustained.
Examples: BAR, FG42, L86A2

Light Machine gun. Full auto anti-personel weapon, bipod, indiv. wespon. Either a large ammo feed or a heatdissapating (quick change, heavy, finned) barrel. But rarely both.
Examples: Lewis gun, BEN gun, RPD

GPMG LMG with a belt feed, quick change barrel, capable of being mounted on a tripod or vehicle.
Examples: MG34, MG42/MG1, PKM, M60, MAG/M240

SAW (Squad automatic weapon) is the base of fire of the rifle squad. Today it usually refers to a weapon very much like a GPMG but chambered fore thew same intermediate power round as the assault rifle.
Examples: Minimi/M24, Negev, Ultimax100, HK MG43

Sustained Fire MGs are robust, heavy weapons almost allways fired from tripods or vehicle mounts. They have large ammo supplies, usually in belts, and heavy, heat dissapating barrels or cooling mechanism.
Medium MG heavy, fixed barrel, often used on vehicles.
Examples: M1919, SG43, Colt M1895
Water Cooled MG (was "Heavy" until after WWII) A sustained fire machine gun that has a jacket full of water to carry off the heat. A WC MG can fire continuously for hours given enough ammo and water.
Examples: Maxim, M1917A1, Vickers

Heavy Machinegun Very large MG firing an anti-material round with a 10-19mm bullet.
Examples: M2, DShK, KPV, BRG-15

http://world.guns.ru/machine/mg00-e.htm

 

[veltyen]

I had always assumed that the GP part of the GPHMG/GPLMG/GPMG designation indicated that it could be squad carried or vehicle mounted.

From what I can find the data appears to support that supposition, but I cannot find any direct references.

It could also be inferred that the General-Purpose indicates the ability to take on both infantry and vehicular targets.

It could also mean both, being extremely general in that case

Anyone got a definitive answer?

 

[Uncle Bob]

GPMGs fie the same ammunition as LMG and MMG. This is not considered adequate for anti-vehicular use.

GP refers to it being light enough to replace a LMG in the squad robust enough to replace a MMG on triod or vehicle.
http://www.army.mod.uk/equipment/pw/pw_mg.htm
http://www.sfu.ca/casr/101-c6orig.htm
AND, best of all,
http://remtek.com/arms/fn/mag/

 

[kaladorn]

1. GPMG is fine for anti-vehicular use, as long as the vehicles are soft skinned (jeeps, trucks, and the like - civilian vehicles won't take GPMG fire very well at all!).
2. You haven't mentioned Medium MGs. That is really what people call the GPMG, it is sort of 'more of the same'. The lines are sometimes blurry between LMG/GPMG or GPMG/HMG.
3. The Vickers hasn't just fired for hours with water cooling, it has fired for (no word of a lie!) DAYS.

Considering the microtubes we can produce now, I can see the possibility of water-cooled MGs once again in some applications, if air cooling isn't sufficient. Or maybe 'other fluid' cooled MGs... (liquid nitrogen, etc?).

I read that piece about the 25mm Barrett. Ouch. I don't know if the study's authors read the same data I did (which is odd when I looked at theirs!), but I certainly would have drawn slightly different conclusions. And dear god, 35 lbs and they are contemplating *greater* weight to reduce recoil? And that's not counting a heavy ammo load.

 

[Uncle Bob]

Problem with the XM109 is that the MV is relatively low, so muzzle brakes are inneffective compared to the .50 BMG. I think attempts to mitigate the recoil will move weight and bulk close to the XM307 OCSW, and it is not that accurate.

GPMG vs. vehicles... small sedans OK, but nothing bigger than 1500 kg unless you can guarranty a full belt or two. .30 MGs were notably innefective against WWII fighters, as the British were not satisfied with even eight.

 

[Straybow]

The multiplicity of MGs on fighters was to enhance hit probability. I believe they used 8 .50s on several US fighters (Corsair, Mustang).

 

[Uncle Bob]

A lot of bullets to get hits i good, but unless each hit can do enough damage you have to pray for a "golden BB."

Six .50 BMG on most US fighters from the P40N to the F86. The idea was to use a gun big enough to damage the target, and use as many as you can firing a fast as possible.
.303 was (or 30-06 or 7.92x57) was marginal against fighters like the Bf109 (or Spitfire). IIRC the eight .303 were replaced by four 20mm when the .303 were found less than ideal against German bombers and the heavy fighters like the FW190.

We didn't have enemy bombers to shoot down, so the limits of the .50 weren't obvious until Korea. The German's replaced their 20mm with slow firing 30mm ad 40mm cannon to hit allied heavy bombers.

 

[Straybow]

There's a huge difference between .303/30-06 and .50BMG as an antimateriel round. American fighters with .50s had no trouble downing FW190s.

 

[Chuck Anumia]

Americans installed .50 MGs on our fighters and Bombers early on in WWII because they had proven their effectivness.
__________________________________________________

 

[Uncle Bob]

Well, at the start of the war .30 MGs were still used on some olde aircraft, and the 20mm in the P38 and the 37mm in the P39 demonstrate that not everyone in the US was satisfied with the .50. But since the 5 ton FW 190 was the toughest target we faced, it was adequate. If the Germans or Japanese had 30 ton bombers like the B17 or B24 the 6x.50 would not be enough.

But the 6x50 in the F86 was marginal against the MiG15 in Korea, which is why all subsequent US fighters had 20mm.

 

[Straybow]

P-38 and P-39 cannon were spinner axis mounted. P-37 also had a couple 20mm in the nose iirc. I think the US designers didn't like wing mounted 20mms.

 

[Todg]

Originally posted by Uncle Bob:
Problem with the XM109 is that the MV is relatively low, so muzzle brakes are inneffective compared to the .50 BMG. I think attempts to mitigate the recoil will move weight and bulk close to the XM307 OCSW, and it is not that accurate.

Actually, muzzle velocity has absolutely nothing to do with the effectiveness of muzzle brakes. Propellant gas expands at a nearly constant rate (given in the literature typically as 4,000fps).

How effective a muzzle brake is depends on the volume of propellant combustion gasses produced and the mass of the propellant compared to the mass of the projectiles.

A higher pressure at the point the muzzle brake is installed does make a difference, and for this reason, some low pressure guns have brakes installed at the middle of the barrel rather than the muzzle.