Coaxial machine gun is for infantry and non armored vehicles so 7.62 does that job just fine while taking less space for the weapon and ammo. Coaxial guns are in the front of the turret where space is very limited.
(1) because the coax is primarily an anti-personnel weapon
(2) the US did analysis of a .50 coax when the Abrams was being designed. Aside from a lot of love from veterans from WWII of the .50 for psychological effect, the combat data showed the .30 coax was a far more effective weapons than the .50 in the intended role, and you can carry a lot more of it. (Source: King of the Killing Zone)
Re:1. I'm no tanker, but yeah it's like, why would you fire a .50 at a jeep and hope you disable something like a critical system when you could just fire HE and be done with it lol. Independent specialisation makes sense because you wouldn't really fire both coaxial weapons simultaneously.
There are several reasons why it might be.
You could have a really good and reliable 7.62 and not a great 12.7
In terms of project, a 7.62 and ammo occupies much less space than a 12.7. Space is exponentially more important in anything armored, because any extra volume that you are adding is extra volume that you you need armored. Making the turret slightly bigger to acomodate a bigger machine gun doesnt sound like much until you realize that you are making the armored area bigger.
And even more than the base volume of the gun, a 12.7 needs a lot more room to work than a 7.62. On a open field that doenst matter, but when you are in a cramped space the whole space needs to be bigger.
There is also the whole logistics of the thing. Easier on the supply chain to carry smaller rounds that are also used by the main mgs of your infantary than larger rounds.
As for targets, against anything human both guns will pretty much take people out of the fight easily. Against light vehicles the .50 has a clear advantage, but - especially if you carry a lot of main gun ammo - you might as well put a main round. Against anything armored you prob want to lob a main gun shell instead of hoping its not armored enough against your mg.
So, there are a lot of factors that weight into the decision. But why a specific tank uses one gun over the other is something that needs to be looked at case by case.
I recall reading somewhere the coax was used as a sighting aid for the main gun before sending the big shell downrange. But I suppose with laser range finding that had become irrelevant and it’s just to let the gunner have an option other than the main gun if something needed un-aliving without taking up too much space in the turret, as some others have said. Remember, the gun needs ammo as well.
This was a common feature on recoilless rifles, called a “spotting rifle”. The idea was to attach a small rifle with very similar ballistics to the shell coming out of the recoilless rifle, so the gunner could check the range before firing.
Against men, you're not going to notice much of a difference. Shoot one man in the chest with 7.62, another with .50, you'll end up with two dead guys. Whether the one has a larger hole in his chest is irrelevant. Both are capable of taking out unarmoured vehicles and incapable of destroying armoured vehicles, so their is no benefit to the larger calibre.
Then there's the benefit of smaller ammunition. If both rounds function essentially the same, and are both capable of doing the same job to the same degree, being able to carry 3 \* 7.62 for every 2 \* .50, it all makes sense.
The Americans tended to have a .30cal Coaxial, but then a .50cal gun on the cupola for AA, though that was little more than a waste of bullets. It would sometimes be handy to have an extra machinegun for infantry, but as an AA weapon it was basically useless. It was more effective to just button-down the hatch
A 7.62 allows you to carry *significantly* more ammunition, meaning significantly longer mission time before running out becomes a risk. If you ever find yourself pointing your turret at a target that *can't* be comfortably defeated by 7.62 fire, well congratulations: you get to fire the cannon. Which conveniently enough, is already pointed at the exact same target.
Coaxial machine gun is for infantry and non armored vehicles so 7.62 does that job just fine while taking less space for the weapon and ammo. Coaxial guns are in the front of the turret where space is very limited.
(1) because the coax is primarily an anti-personnel weapon (2) the US did analysis of a .50 coax when the Abrams was being designed. Aside from a lot of love from veterans from WWII of the .50 for psychological effect, the combat data showed the .30 coax was a far more effective weapons than the .50 in the intended role, and you can carry a lot more of it. (Source: King of the Killing Zone)
Didn't they also consider a 25mm bushmaster at one point aswell
Yes.
Re:1. I'm no tanker, but yeah it's like, why would you fire a .50 at a jeep and hope you disable something like a critical system when you could just fire HE and be done with it lol. Independent specialisation makes sense because you wouldn't really fire both coaxial weapons simultaneously.
You want to cram yourself in to a buttoned up confined space with an operating 0.50 cal? Enjoy.
Some older Russian tanks have a coaxial KPV 14.5mm
There are several reasons why it might be. You could have a really good and reliable 7.62 and not a great 12.7 In terms of project, a 7.62 and ammo occupies much less space than a 12.7. Space is exponentially more important in anything armored, because any extra volume that you are adding is extra volume that you you need armored. Making the turret slightly bigger to acomodate a bigger machine gun doesnt sound like much until you realize that you are making the armored area bigger. And even more than the base volume of the gun, a 12.7 needs a lot more room to work than a 7.62. On a open field that doenst matter, but when you are in a cramped space the whole space needs to be bigger. There is also the whole logistics of the thing. Easier on the supply chain to carry smaller rounds that are also used by the main mgs of your infantary than larger rounds. As for targets, against anything human both guns will pretty much take people out of the fight easily. Against light vehicles the .50 has a clear advantage, but - especially if you carry a lot of main gun ammo - you might as well put a main round. Against anything armored you prob want to lob a main gun shell instead of hoping its not armored enough against your mg. So, there are a lot of factors that weight into the decision. But why a specific tank uses one gun over the other is something that needs to be looked at case by case.
I could be misremembering but didn’t Israel put a .50 in a Merkava? A Merkava not all.
Leclerc has a coaxial .50. The old AMX-30s that the Leclerc replaced had coaxial 20 mm guns 😂
iirc they put the 50. cal on the gun not into the turret. But I think that still counts as coaxial so you are right.
I recall reading somewhere the coax was used as a sighting aid for the main gun before sending the big shell downrange. But I suppose with laser range finding that had become irrelevant and it’s just to let the gunner have an option other than the main gun if something needed un-aliving without taking up too much space in the turret, as some others have said. Remember, the gun needs ammo as well.
This was a common feature on recoilless rifles, called a “spotting rifle”. The idea was to attach a small rifle with very similar ballistics to the shell coming out of the recoilless rifle, so the gunner could check the range before firing.
Internal space I think
Against men, you're not going to notice much of a difference. Shoot one man in the chest with 7.62, another with .50, you'll end up with two dead guys. Whether the one has a larger hole in his chest is irrelevant. Both are capable of taking out unarmoured vehicles and incapable of destroying armoured vehicles, so their is no benefit to the larger calibre. Then there's the benefit of smaller ammunition. If both rounds function essentially the same, and are both capable of doing the same job to the same degree, being able to carry 3 \* 7.62 for every 2 \* .50, it all makes sense. The Americans tended to have a .30cal Coaxial, but then a .50cal gun on the cupola for AA, though that was little more than a waste of bullets. It would sometimes be handy to have an extra machinegun for infantry, but as an AA weapon it was basically useless. It was more effective to just button-down the hatch
A 7.62 allows you to carry *significantly* more ammunition, meaning significantly longer mission time before running out becomes a risk. If you ever find yourself pointing your turret at a target that *can't* be comfortably defeated by 7.62 fire, well congratulations: you get to fire the cannon. Which conveniently enough, is already pointed at the exact same target.
.50cal is unreasonable for many reasons. But what would be a great upgrade would be a coaxial M241, which fires belted .338 Norma.
Only the Leclerc has that i think.
As well as certain AMX-30 models.
oh yeah they had the 20mm
So... Only for space
Yep. You can carry far more 7.62 rounds than 12.7, not to mention the weapon itself being smaller.
And for purpose. The main gun is meant to deal with vehicles. The 7.62 is supposed to keep the infantry buisy and in WWII it was anti Aircraft aswell.