MGs fire trajectory-grazing fire affecting multiple units

[dalem]

For what it's worth, I was looking through my "U.S. Armored Infantry Battalion Tactics In WWII (FM-17-42 - Armored Infantry Battalion)" by Nafziger for something unrelated and I came across this in Section V. MACHINE GUN PLATOON:

"92. GENERAL

...c. All members of the platoon are trained in indirect firing. Indirect firing may be employed when appropriate."

Whether it means what we were discussing or was actually trained on or practiced in the field, I have no idea. But I found it interesting given this thread.

-dale

[cassh]

I've posted before on this subject, but cannot remember if it was this or the old CMBO forum from way back.

Anyhow - I did a stint in the battalion SF Platoon as a section commander. We had SF (sustained fire) GPMGs (equivalent of the M240).

I have to admit complete ignorance to the term 'grazing fire' until a few years ago. The main reason for this is that although clearly an accurate way to describe the use of 'flat trajectory' fire, it doesn't come up in a tactical sense.

That is not to say it is not used, because it is, it is just that more often than not it is the by-product of ranged fire. This is because one rarely if ever engages a target without setting the sights to a range/elevation (whether merely iron sights or an optical device such as the C2 unit). This would defeat the whole purpose of an SF weapon, namely laying down fire 'on' a target. The setting of range means the fire hits the targets in the target area (beaten zone) at waist height anyway.

People have mentioned grazing fire being synonymous with FPF. This is not always the case. Firstly for an SF gun team FPF is not necessarily you're own FPF. An SF shoot can be pre-registered in one of you arcs as what for you is a standard SF shoot, but for FF is their FPF. Only your own SF101 FPF shoots constitute genuine flat trajectory fire in most circumstances. 'Grazing fire' cutting through a target a waist height only really comes in to play for short-range shoots and the guns own FPF. Final protective fire uses pre-sighted/registered fire on marked fixed axes along the immediate line of your own positions/troop line. These still have recorded range/elevation that corresponded with the end of the position to be protected from overrun (e.g. if you SF Pln position is 200m across the gun invariable will be recorded range 300m on a target/aiming point knee high at 200m along the desired path. In this way you pretty much guarantee anything between knee high to chest high from 0m - 400m stands a severe chance of a rainy day if the stumble into your LOF.

One of the selling points of the SF GPMG, like its design parent the MG-42 is its flat-trajectory. So unless deliberately elevating to go over FF heads as they manoeuvre, the combo of the LOF trajectory (grazing fire) and the beaten zone will generally nail anyone stupid enough to be in its path. BTW a beaten zone is not a cone shape as someone mentioned above, but an elongated ellipse pointing down the axis of fire in the target area.

The point this longwinded post is trying to get across is that grazing fire occurs more so at shorter ranges (under 600m) and less so at extended ranges, and therefore this should be easier to model depending on the gun being modelled.

The easiest way to help explain the physical model of MG fire is a garden hose. Higher velocity rounds run truer and flatter (MG-42/FN GPMG) like a high-pressure hose. Lower velocity rounds (vickers) must be arced up to plunge on their targets to reach longer ranges. This corresponds to just as you do with lower water pressures when trying to reach the back of the flower bed/car pointing the hose higher up. But up close, the difference in pressure is not as noticeable, at if the hose is pointed at you, you still get hit with water smack in the face.

Things that would be nice to see 'fixed' re SF MG in CMx2

1. Ability to fire pre-registered targets (say five per team) in day/night/fog/smoke etc.

2. Ability to fire deilade/indirect fire like mortars with spotting HQs if wpn trajectories permitted.

3. As mention in another post, penalties in ammo levels for any move by MMG/HMG teams without vehicles.

4. Better ballistics model for MG fire / small arms fire whereby range/elevation/weapon and target all effect intervisability type factors of LOF trajectory.

a)This would introduce grazing fire effect at shorter ranges which tapers off as ranges increase.

b)Chances of blue-on-blue from small arms likely if arcs crossed or entered by FF at shorter ranges - hopefully player would then use MMGs/HMGs historically from deep overwatch positions using arcing fire that won't mow down their own troops but go over them to plunge in on the enemy target.

Now I must stop as I have even bored myself...

[Simon Fox]

Originally posted by cassh:

The easiest way to help explain the physical model of MG fire is a garden hose. Higher velocity rounds run truer and flatter (MG-42/FN GPMG) like a high-pressure hose. Lower velocity rounds (vickers) must be arced up to plunge on their targets to reach longer ranges. This corresponds to just as you do with lower water pressures when trying to reach the back of the flower bed/car pointing the hose higher up. But up close, the difference in pressure is not as noticeable, at if the hose is pointed at you, you still get hit with water smack in the face.

I don't want to pour cold water on your otherwise interesting post BUT as far as I know there is little difference between the muzzle velocities of the MG42 and the Vickers.

MG42

755m/s

Vickers

MkVII round

743m/s

MkVIIIz round

777m/s

Anyway the MG42 was a dud. Too heavy, cumbersome and ammunition hungry for a section weapon and with too high a cyclic rate and insufficiently reliable for sustained fire.

[cassh]

Well it will be a combination of muzzle velocity, weight of shot and gun mechanism that determines trajectory, and it is known that Vickers had a less flat trajectory than MG-42.

Therefore if not down to MV, it must either be the weight of round/MV combination to give a differing kinetic energy or the fact they fire from a fixed mount rather than a recoil buffered gun mount.

Regardless, the analogy with hose holds true; an elevated gun will produce plunging fire at range and weapons with 'flat trajectory characteristics' will produce grazing fire out to a longer range.

Toddles...

[ March 30, 2005, 04:13 AM: Message edited by: cassh ]

[cassh]

Oh, BTW:

MG-42 actually, not a dud at all. One of the finest weapons ever designed IMHO.

As a company/battalion support weapon in SF role it was absolutely awe inspiring in its design and ingenuity. The fact that western GPMGs have copied it to greater of lesser degrees, and its offspring the FN-MAG GPMG (M240) is very much still in use in both the light and SF role would lead one to believe today’s current armies hold a differing view to the attributes of this weapon. A high cyclic rate is not a problem in itself. You merely adjust your firing method to shorter burst. As long as you put the same amount of fire down (number of rounds) the guy on the receiving end aint gonna quibble whether its 1200, 700 or 400 rpm. Its just with an MG-42 the gunner needs good fire discipline and training to conserve ammo and prevent overheating.

[Wartgamer]

Final Protective Fires, where non-stop firing occurs, is usually the domain of a water cooled MG.

In most situations where you want the enemy to 'walk' through the 'stream', you are not firing that long. Typically a small group (squad/section) will be seen rushing a distance. You aim ahead of them and keep the aim there. If you hit one or two of them or your tracers are sensed by them, they will usually go to ground. If they do not, pick another line ahead of them and repeat. Anything else you hit/supress along the line is just lucky gravy.

In the case where they are coming directly at you (perpendicular line), you are best off firing short bursts at individuals.

The sMG42 (tripod) was not a dud. The MG42 bipod was perhaps a misapplication of a platoon GPMG in the squad automatic role. The MG42 bipod could perform the above drill better than most slowly firing magazine fed SAW.

[ March 30, 2005, 09:34 AM: Message edited by: Wartgamer ]

[Andreas]

Originally posted by cassh:

A high cyclic rate is not a problem in itself. You merely adjust your firing method to shorter burst. As long as you put the same amount of fire down (number of rounds) the guy on the receiving end aint gonna quibble whether its 1200, 700 or 400 rpm. Its just with an MG-42 the gunner needs good fire discipline and training to conserve ammo and prevent overheating.

Therein lies the rub. While the guy on the receiving end is not going to quibble, your ammo supply person is, and since the guy on the receiving end is not going to quibble anyway, why not use 800 RPM instead of 1,200? At least that is what the Bundeswehr was doing postwar.

That does not make it a dud by any means, but the high cyclic rate was a significant drawback for the Wehrmacht with its already strained logistics, and declining recruit qualities as the war went on.

[rleete]

Andreas, I think you're quibbling, so you should receive between 800 and 1,200 rounds per minute.

[Andreas]

That'll shut even me up.

[JonS]

oh please god! let it be TRUE!