schnuersi said:

BTW apparently we have both been wrong since the PKP still has the QCB option and the force cooled is just a special type of barrel.

Yes, I noticed that.  Although since Max says the PKP is not issued with a spare barrel, the effect is the same as if it did not have a QCB.

There are in my opinion three ways to keep pasively air-cooled machineguns from overheating:

1: Keep the rate of fire down: 

+ Allows for a relatively large load of MG-ammunition to be carried by the squad, while saving the weight and bulk of the spare-barrel.

- Low rate of fire, or risk ruining the barrel, or even leaving the MG-unoperable.
 

2: Have one or more spare barrels:

+ Allows for a high continous rate of fire.

- Adds bulk and weight, reducing the amount of ammo available, and is not disposable.
 

3: Have more machineguns available:

+ Allows for the highest rate of fire from the squad, both instantaneous and continous, higher ammunition load than alt#2, but lower than alt#1  and also being able to fire at more targets at the same time, or fire at the same target from different angles.

Adds redundancy.

Allows lighter machineguns, and even magazine-fed machineguns)

- Doctrine has to be changed to utilize them effectively.

200 and 250 round boxes are used only for PKMS or vehicle-mounted PKP

Note that they do not have a clip to attach it to the gun

In LMG role it's almost exclusively 100-rd boxes that are clipped on to the gun

I mean in the manner of focusing the squad around supplying and supporting the SAW/LMG. An extreme example is the WW2 Germans. Where the squad was built around supporting the MG34/42 and worked to support it almost entirely. As in the squad existed to almost to simply facilitate the use of the MG. While few militaries ever replicated that heavy focus as much, most did learn their lessons from it and its effectiveness. And worked post WW2 to have it so that there was a gunner-assistant team and the rest of the squad carried some manner of spare materials to feed the SAW/LMG.

That still exists in the way of most members of a current US squad carrying at least some belted ammo for the M249. And sometimes a spare barrel or so.

Given that our main enemies for the last few decades have been irregular forces, I don't believe we can properly say how effective the organization would be against a real enemy. Anything short of WW2 era equipment would put us above insurgents in the Middle East in terms of modernity and quality. As stated before, during Vietnam, which was closer to a proper war than what we see today, even if still distant. M60s were issued to gunner-assistant pairs.

Generally outside of the Garand and the M1 Carbine, the US went into WW2 and came out of it with a pretty outdated set up. FWIW, the 1919A6 did have a QC barrel however.

Apsyda said:

FWIW, the 1919A6 did have a QC barrel however.

That's not what I recall from my time in high school ROTC.  And it's sure not what is shown here, either.

YouTube

1919A6 Full Auto - Shooting and Disassembly

This video covers the 1919A6 We will do some shooting at the range, and then do a table-top overview and disassembly. We will go over headspacing and functi...

The M1919A6 barrel could be changed quicker than the M1919A4.

M1919A6 barrel could not be changed nearly as quickly as the MG34 or MG42. 

That M1919A6 is  the best looking machine gun ever!

I'll second that emotion!

PKMS and an RPG-16? Dude is hardcore!

Or watched too many bad movies.

So the question here is why are army saw gunners not carrying spare barrels?

And it's a very what came first the chicken or egg problem because there's organizational things that actively contribute to this.

For me there's also another question which is equally important.

Do we even want SCHV belt feds?

One issue with schv belt feds is they really don't hit any harder or give you more reach than your carbines.