Regarding reasons not to opt for shock mitigation: Sure, it depends on what you want to emphasize, what your doctrine and concept of employment is, what the threat is, how you mitigate risk and what tradeoffs you want to accept.  

Even before shock mitigating seating the number of dismounts for IFVs was compromised compared to an APC simply because the turret takes up space.

Now you can choose between more dismounts (back up towards more effective squad sizes) AND a medium caliber cannon, or the same number of dismounts with shock mitigation. Which goes back to my post over on the Elbonia thread: what do you want?  Do you want light infantry capable of fighting independently of the AFV, or do you want a small detachment intended to only fight with their direct support? Or do you want both? 

If we decide to go both, do you compromise on squad sizes for the sake of the limitations of the AFV, or refuse? Do you opt for larger vehicles, same sized vehicles without shock mitigated seating, or simply more vehicles in a platoon to carry all the people?  It's not straightforward.

RovingPedant said:

I'm building the case that vehicle mounted single barrel MGs usually have provision to change the barrel, presumably because you need to change the barrel

If you want to build the case around such a broad statement you would have to define "provision to change the barrel" and "need to change".

Because I would callenge that. Lots of vehicle mounted single barrel MGs do not have this. The vast majority of RWS do not. Remote controlled turrets have not. All .50 cals don't. For the simple fact that even though its called QCB its by no means quick and convenient to change the barrel of an M2. At least not compared to the vast majority of GPMGs used on vehicles. For me a QCB must be as quick and easy to change as in a MG3, FN MAG or PKM. If the M2 qualifies lots of 20 mm cannons do as well.
From my point of view the vast majority of rifle caliber machine guns mounts, mounted under armor protection and reachable by the crew of a purpose build AFV do allow for barrel change. Lots of pintle mounts do as well or better don't interfere with barrel change. But that is about it.

I have been talking specifically about coax mounting. I am willing to broader my arguments to the above. The arguments I listed and will list would still be valid.
I am not talking about remote controlled use. This is different. That doesn't mean I think a minigun is a good choice for that unless the ROF is desired but the arguments are different and some of what I wrote would become invalid.

RovingPedant said:

A minigun weighs 26kg*. The (electrically powered) L94A1 chaingun weighs 18kg plus a spare barrel. The barrel change RMG 7.62mm weighed 35kg.** Fire control requires electrical power.

Weight is not the issue.
For use under armor volume is. A minigun is big. Also the entire barrel cluster would need the be at least partially outside. Resulting in a significant hole in the armor.
In additon because of the poor accuracy more ammo is needed for the same effect. Further increasing the required volume.
The beatuy of the L94/chaingun is that it is very compact. It basically offers the advantages of a minigun in a much smaller and more convenient package. At the same time it doesn't have the same drawbacks.
The RMG doesn't really exist so IMHO it should be ignored. It also has specifically been developed for use in RWS.

If barrel change is required and if yes how often is the question. Since in AFV with manned turrets coax guns usually are reachable there has been no need to use specialised gear. The standard issue GPMGs with some standard spare barrels do just fine.
Even in coax use the ready to use ammo supply is usually 500 rds or less. Sometimes 1000 rds but more often than not its a second 500 rds bin that allows for quick belt replacement. Which also needs interference by a crewmember. So in a worst case scenario a MG mounted inside a vehicle can fire 1000 rds in one long burst. If this would be concidered a necessity or real problem heavy barrels or barrel with cooling of some sort that allow for 1000 rds to be fired trough them in one long burst would be issued. For a long time. If the problem became a thing recently we would see a recent move in this direction. But we don't. What we see are some militaries issuing heavy barrels with somewhat more heat capacity.

In RWS the number of ready rounds is usually even lower. So at best it would be an issue for the RWS mounts that can be reloaded under armor but barrel change can not be done. Even here we don't really see any serious development to solve "the problem". A couple of years ago concept like the RMG poped up but found not takers. Some heavier barrels are issued now by some. For most part we see an increase in weapon size. RWS moved aways from GPMGs to HMGs and 40 mm and now there is a conciderable move towards ACs. In some cases with additional GPMGs as secondary.

RovingPedant said:

If you need a weapon that is located somewhere that you cannot manually change the barrel and the barrel change RMG is a consideration

I am not a fan of the RMG concept but its still is conciderable superiour to a minigun. Its accurate!
An actual sensible solution would be to mount a second GPMG with half of the ammo. Two MG3 don't weight 36 kg. Alternate using would allow for at least double the number of rounds fired. If high ROF is need (anti drone) both could be fired at the same time.
Light weight, only needs minimal power, accurate and no new equipment is needed. Of course the same could be done with an FN MAG or whatever GPMG.
BTW this used to be the solution picked in the past for cases when MGs had to be mounted on AFV that could not be directly serviced by the crew.
The Strv has two FN MAGs mounted in a box on its bow.

RovingPedant said:

I kind of like the concept for a remote gun and the only show-stopper I can see is the increased dispersion and cost.  

...and it is massive.
Miniguns are only usefull if you need lots of shots downrange fast, for a significant time and if its not important that most shots will miss and that it might take a couple of dozen rounds fired until a hit is scored.
Which makes it a poor or even impossible choice for most uses.

RovingPedant said:

Such as?

As mentioned: use two GPMGsor a purpose designed barrel.
A cooling device is also an option.
Even for high ROF a minigun is not the most efficient option. High rates of fire can be reached by other gun designs without the volume and dispersion of a minigun.

RovingPedant said:

* 32kg with the gun control unit

For 39 kg you can get a 20 mm AC. Or 3 MG 3 for ~34 kg.
3 MG 3 would allow for 750 rds of continous fire under peace time regulation if used one after the other. Or if they all fire at the same time match the ROF of a minigun. While having much less dispersion and being self powered.

Unless you want to fire several hunderets or thousands of rounds very fast and have no problems with volume and ventilation I really see no need for a minigun.

YouTube

Ma Deuce vs. Minigun | TRIGGERS

Wil Willis compares the M2 and M134 in their medium range accuracy. | For more TRIGGERS, visit http://military.discovery.com/#mkcpgn=ytmil1Subscribe to Milit...

Just to throw some fuel on this fire 

Refleks said:

Just to throw some fuel on this fire 

What is happening to the Minigun at the end of the firing? A round firing out-of-chamber?

Noticed that too, I thought hangfire at first but someone in the comments suggested leaving the trailing link empty would cause a malfunction which might explain why it happened at the very end.

It's a silly test but fun anyway!  

I'll see your Ma Deuce vs Minigun, and raise you QUAD Ma Deuces vs QUAD Miniguns.  

YouTube

Shooting Quad 50's, 400 rnds

Green Mountain Boys Machine Gun Shoot, 2016. 400 rnds quad 50

YouTube

THIS QUAD MINIGUN IS INSANE 4K ORIGINAL

Was recently at the Big Sandy Shoot and got to witness history from Dillon Precision the QUAD minigun a dream 30 years in the making powered by helicopter ba...

That's not a rigid coaxial mount ;)

Also, I am with @Schnuersi here (d'uh) - Given that Germany had a prototype for a coaxial gun that could rotate between 3 barrels if one overheated and that was not deemed necessary. I think you have a solution without a problem. The fact that nobody uses a coaxial minigun seems to indicate this.

Wrong guy, I didn't suggest using miniguns as a coax and I don't have a dog in this fight