250 rounds per minute is a bit low from what Ive seen and read (ive never see an MG42 firing, but I have seen an M-60, which is based on the German gun.....it has a practical rof much higher than what you are saying). At 1200 rpm it will tear through barrels quickly, if fired at that rate continuously, but not so quickly if there pauses in that fire. Changing a barrel for an MG 42 was an easy and quick operation.
While I have fired a single 50 round belt from an MG 42 It doesn't qualify me as a MG expert
However please note that that the MG 42 barrels were plain steel and would wear out much quicker from high fire rates than an M-60s stelite lined barrel. While text book fire rates were often exceeded in combat it was given that the MG-42 should be fired at so many rounds per minute and the barrels changed every few minutes. The barrels were rotated so no single barrel was burned out too quickly.
Even at one belt (250 rounds) per minute the Vickers started boiling water in just a few belts and then evaporated water at the rate of one pint every belt or so.
The Germans could and did use the MG 42, as a support weapon, without the tripod that you referring to. As an improvisation, they would use a second crew member. The bipod at the front would be held by this second crew memeber, to keep the gun more stable. Realistically, the gun would require a minimum of 3 members to function efficiently, but the returns for this investment were well worth it.
this "expedient" was usually used because of tall grass or some other obstacle that prevented normal use of the bipod. Laying the gun across somebody's back or shoulder while they grab the bipod is no substitute for a tripod. Or if you are referring to placing the bipod on the ground and having somebody try to hold it the results aren't going to be a lot better. the rear end of the gun is unsupported except by the firers shoulder and the recoil of 20shots a second WILL move the point of impact even at 100yds. Short bursts are needed with frequent re-aiming. During my very short exposure to this weapon I never got off less than 7 shots per burst although trained gunners with more experience could get off 3-4 round bursts.
ME"Most tripod MGs could only put out 200-250 rpm effectively for more than a few minutes time with the LMGs being good for 100-150rpm..."
Agree with your conclusion, though your numbers are low to me for the MGs
I am trying to use numbers I have seen published as either doctrine or practical. For example the Bren gun was supposed to fired at 4 magazines per minute and barrels swapped every 2 1/2 minutes or 10 magazines in a sustained fire mission. Post war Brens converted to 7.62 NATO often (always?) had chrome lined barrels which stood up to the firing better.
It is the barrel cooling that limited the practical rates of fire more than anything else. Somebody once fired a French AA 52 for 500rounds using linked belts, According to the story there was no rifling left in the barrel for almost 300mm in front of the chamber. Yes the gun will still fire but any hope of accuracy is long gone.
As noted, Chrome lining and especially stelite will significantly change the the rate of barrel wear.
Over heating guns can lead to jams and other problems. Melvin Johnson once wrecked a BAR with about 700 rounds. Gun was fastened down and trigger tied back and magazines changed as fast as possible. For-end was smoking before 400 rounds with visible flames not long after. Gun ceased functioning just over 700 rounds when the mainspring (which had lost it's temper) would not return the bolt forward. Please note that the Russians changed the location of the mainspring on the DP light MG from under the barrel to a tube out the back of the receiver on the DPM.
Is your German example including artillery ammunition?
I do have some figures for a US infantry regiment in the summer of 1941. I am not claiming that this was ever used in combat but it does show what they were thinking in 1941. EACH BAR was allocated 820-860 rounds (depending on which type of rifle squad it was in) on the "unit ammunition train" in addition to the 320 rounds carried by the solder with the weapon. of the ammunition on the unit Am Tn 468-500 rounds were to issued before combat. Another 540-576 round were carried on the ammunition train of a higher unit. The numbers change because of the ammunition in bandoleers. 60 round bandoleers for Bot rifle equipped troops and 48round bandoleers for M-1 equipped troops.
The numbers for the Browning 1919 air cooled MG are 3000rounds on the prime mover or or ammunition truck, 2000 more rounds on the unit Am Tn and a further 1000rounds on the train of a higher unit. 6000 rounds total compared to the 1720- 1748 for each BAR.
The 1917 water cooled Brownings were supplied with 6750 rounds on the prime mover or ammo truck with another 1500 rounds on the higher unit ammo train for total of 8250 rounds.
Granted ammo could be redistributed to cover shortages but obviously the water cooled guns were expected to provide the sustained fire support.
I think you may have mad a slight error in the ammo available for the Bren gun in New Guinea. Bren gun magazines hold 30 rounds (or often 28 to aid reliability). 25 magazines with 28 rounds apiece is 700 rounds. Yes you can use loose ammo or pull the ammo from stripper clips during lulls in the battle but even at my 120 rounds a minute 700 rounds in magazines is going to last under 6 minutes. How fast can a couple of squadies reload the magazines?
Me"The advantage of the GPMG was that it simplified logistics and training over maintaining two (or three) different guns in the army."
I agree, but thats not the only advanatage. If the fire exercise required sustained fire, a belt fed gun could do longer burst, and variable length bursts. A magazine fed weapon is always limited by the size of the magazine, and though they could be reloaded at intervals, in a hot close assault where it was important to keep the enemy's heads down, the brens and BAR type guns were at a disadvantage. In fact they couldnt really do the job as a single weapon.
I don't believe anybody was just holding the trigger back on air-cooled MGs of any description. Even Vickers gunners were taught to fire 4-5 round bursts. They just space the burst a bit closer.
Agree with all of this, except weapons that you refer to as "bn guns" were always attached to companies platoons or even squads when being used. They were commanded by Bn HQ,in the sense that they would be distributed by them, but used by the subordinate formations. This was applicable to all formations that enjoyed a heavy weapons company, these formations were not kept in a concentrated park in the same sense as artillery was.....they were distributed to the subordinatee formations as needed (with the crewws of course) . With regards to you last statement, that is only partly true. Vickers guns were the least mobile of the support guns, MG 42s were as mobile as a Bren or a BAR, and 30 cals almost as mobile. If the platoon or the squad advanced beyond the range of the support element, it would not be unreasonable to expect the support guns to move up with them. The Russians certainly thought this with their whelled "sokolov mounts" for their heavy maxim support guns.
When guns were detached for use by subordinate units, they were often detached in pairs or platoons of 4. They were often used for long range fire or place to enfilade an enemy position or expected attack route. They would usually be part of a battalion fire plan, either in attack or defense. In some circumstances (thick jungle or woods, city streets, very mountainous terrain) with restricted fields of fire they might be parceled out to small units to use as they see fit but these guns are a very important part of the battalions firepower, for a Major to surrender control of these weapons to Sargent or corporals to do with as each sees fit doesn't seem like the best use.
Be sure not to confuse a squad with a Vickers gun in company and a Vickers gun with a squad in company for local security.
As far as movement and the LMG use, it is precisely why the LMG came into wide spread use. In WW I the Vickers and Maxim guns could not keep up the the attacking troops. The LMGs (Lewis, Chauchat, etc) could be brought forward and provide automatic fire from the new forward positions WHILE they waited for the heavier guns to be brought up. In many cases a fold of ground,a stand of trees or buildings could block the line of fire from where the tripod mounted guns were or the LMG was in a vantage point (just over a low ridge) were it could hit targets the Heavy MGs couldn't even if they were only a few hundred yds away.
And please do not confuse the LMG version of the MG 42 ( or it's capabilities) with the tripod mounted version. While the LMG could be mounted on the tripod with extreme speed without the tripod and the long range sight it had very little long range capability. Without extra barrels and copious amounts of ammunition the LMG MG 42 cannot perform support fire missions like Vickers guns.
While Russian troops dragging their "sokolov mounts" at the run in attacks make great propaganda photos they also make great targets for any Germans who can see them.
The big guns ideally support the attack as the troops move forward, then move forward themselves as the leading waves/s cover the big guns advance (change in firing position) with their lighter automatic weapons and rifles. Repeat as needed until ultimate objective is reached. Vickers guns, Maxim guns and the like do not lead attacks or accompany leading waves except in extraordinary circumstances.