Hi guys, help me out here, I a, trying to understand something

Apparently in WWI, Germany went with a lower ROF in its machine guns to preserve ammo. I can't remembe where I read that and I will treat this as unconfirmed. In WWII ermany went with >1200 RPM. What was the rationale?

These days we are looking at XM250 with what - 5...600 RPM? And LWMMG and successors (SIG) similar?

What is the reasoning behind low vs high RPM? 

Also 6.8x51 would appear to be the GPC (Congrats Tony!) And people on this forum seem to agree that 8.5mm in a machine gun is a solution in search of a problem. remind me why? 

Just to throw it out there, keep the SAW at 6.8mm soft recoil and low RPM and have the GP/M MG at the high RPM and 8.5mm?

graylion said:

Apparently in WWI, Germany went with a lower ROF in its machine guns to preserve ammo. I can't remembe where I read that and I will treat this as unconfirmed.

Never heard of that. The M08 and MG08/15 have a ROF of 600 rpm. It was increased from 500 rpm around 1916 by using a modified mechanism and a recoil booster.

graylion said:

In WWII ermany went with >1200 RPM. What was the rationale?

Not really. They went with as high as they could get. The MG 34 cycles ~900 rpm. Later versions ~1000 rpm. The MG 42 1500 rpm. The successor to it the MG 45 would propably have cycled ~ 1800 rpm.
The MG 3 with uses the less powerfull 7,62x51 and not the 7,92x57 cycles around 1200 rpm. This somehow lead people to believe the MG 42 did as well but it cycled faster.

The rational behind it is to get the densest possible burst pattern to get the maximum possible hit chance per burst. Especilally under combat conditions: short target exposure time, unknown range, tried soldiers, bad lighting etc.
From mount in the MMG role it creates a very dense beaten zone. Combined with the very sofisticated mount in use then, that could move in a setable pattern by using the recoil force of the firing gun, it was possible to get a lot of aimed fire on target in a very short time. At ranges behond 1000 m the first 50-100 rounds would impact the target zone befor the firing of the gun could be heard. Against an advancing enemy this would allow a MG to inflict multiple casulties befor the targetet enemy could react.

graylion said:

What is the reasoning behind low vs high RPM?

The reasoning behind low RPM is that its easier to use because the gunner can stay on the trigger longer.Its possible to build lighter guns and it has lass wear and tear.
Its also more accurate and less ammo consuming under shooting range conditions.

schnuersi said:

The rational behind it is to get the densest possible burst pattern to get the maximum possible hit chance per burst. Especilally under combat conditions: short target exposure time, unknown range, tried soldiers, bad lighting etc. From mount in the MMG role it creates a very dense beaten zone. Combined with the very sofisticated mount in use then, that could move in a setable pattern by using the recoil force of the firing gun, it was possible to get a lot of aimed fire on target in a very short time. At ranges behond 1000 m the first 50-100 rounds would impact the target zone befor the firing of the gun could be heard. Against an advancing enemy this would allow a MG to inflict multiple casulties befor the targetet enemy could react. graylion said: What is the reasoning behind low vs high RPM? The reasoning behind low RPM is that its easier to use because the gunner can stay on the trigger longer.Its possible to build lighter guns and it has lass wear and tear. Its also more accurate and less ammo consuming under shooting range conditions.

I take it you would suggest high ROF for MMG? Also for SAW? Even on bipods and not Lafette?

graylion said:

Also for SAW? Even on bipods and not Lafette?

Especially from bipod in the LMG role.
Here these points:

The rational behind it is to get the densest possible burst pattern to get the maximum possible hit chance per burst. Especilally under combat conditions: short target exposure time, unknown range, tried soldiers, bad lighting etc.

fully apply. For MMG use the improvement is not that big but LMG use it makes a huge difference.

schnuersi said:

graylion said: Also for SAW? Even on bipods and not Lafette? Especially from bipod in the LMG role. Here these points: The rational behind it is to get the densest possible burst pattern to get the maximum possible hit chance per burst. Especilally under combat conditions: short target exposure time, unknown range, tried soldiers, bad lighting etc. fully apply. For MMG use the improvement is not that big but LMG use it makes a huge difference.

So all those recoil mitigating mechanisms are the wrong way, since they slow down RoF? Try and design an LMG/SAW in 6.8x51 and highest possible RoF and find a bear to carry it? ;o)

graylion said:

So all those recoil mitigating mechanisms are the wrong way, since they slow down RoF?

IMHO and that of many others: yes. Ideally you would reduce recoil while keeping the ROF high. If that is not possible high ROF is to be prefered.
One of the main reasons why the MG5 is so controversial in the German military is its low ROF... among other things. The MG3 is still highly regarded and seen as the gold standard.
 

graylion said:

Try and design an LMG/SAW in 6.8x51 and highest possible RoF and find a bear to carry it? ;o)

6,8x51 is not so different to 7,62x51 and less powerfull than 7,92x57. The MG34 and MG42 used the latter and both guns where highly successfull in the LMG role. So is the MG3 which uses the 7,62x51. An average build european male can easily carry a 12 kg MG plus ready ammo. Has been done in the past and is still done today.

The LMG gunner should be strongly build in any case. Its allows for better gun/recoil controll and means he gets less tired while carrying. The LAW/RPG/Panzerfaust also isn't given to the one 1,65 m, 60 kg guy in the squad. Somtimes being tall and strong is an advantage.

schnuersi said:

An average build european male can easily carry a 12 kg MG plus ready ammo. Has been done in the past and is still done today.

LMGs are getting lighter anyway ...

So what about 8.5x63 for MMG with recoil moderating mechanism?

schnuersi said:

The MG3 is still highly regarded and seen as the gold standard.

Most reports I've seen have the MG3 set to a more sedate 850-900rpm (for example, Austrias MG3.)

Was that the case in Germany, or did they retain the higher RPM bolts?

graylion said:

6.8x51 would appear to be the GPC (Congrats Tony!)

No, not even close.  Tony's GPC was significantly smaller and much lighter than 7.62 NATO.

_____ 5.56 NATO ________ 6.5 GREN ___________ 6.5 GPC ____________ 7.62 NATO _______________

6.8x51 SIG is the same size -- and nearly as heavy -- as 7.62x51 NATO.

graylion said:

Also 6.8x51 would appear to be the GPC (Congrats Tony!) And people on this forum seem to agree that 8.5mm in a machine gun is a solution in search of a problem. remind me why? 

I think that a 80,000psi 6.5 Grendel or 6mm ARC (using Sig Hybrid tech) would be closer to Tony's GPC.

From what I recall, the 8.5mm machine gun just does not add enough capability to worth the trouble.  The bullet is to0 small to carry enough HE for anti-material roles, so it can't really replace the 50 BMG.