I'm wondering if there are going to be two versions of the heavy bolter.

Because in the Canon there are the belt-fed heavy bolters you see, but there' also a large box magazine style.

We could see both and have them have different advantages?

Yes, there will be both mag-fed and belt-fed versions.

I would think the belt feed uses heat because it never runs out of ammo. So if you are good at staying alive, then belt would be the way to go, otherwise box feed will work.

With the belt fed HB the advantage would be that you only ever have to stop shooting when you overheat. But like in space marine you can shoot a little after the overheat has diminished but overheat faster, which might not be enough to kill someone with with that amount of heat left. Box mag HB would load a lot faster than it would take to 'unoverheat?', disadvantage being you have to reload when your out of bullets which takes longer than waiting for you to 'unoverheat' just a little bit! That was self explanatory though right??

To me the advantage of belt feed is you don't run out of ammo. The disadvantage is that it overheats.

Box feed has the advantage of not overheating, with the disadvantage of running out of ammo.

SO there I was in the army, late at night, the range OIC walked down the line telling every one to shoot up everything they had at that position, I looked over to my AB and was like you" heard the man" we linked up everything, and I had 6 years of Machine Gunner experience at the time, I was using 6-9 round burst every 4-5 seconds like a smart kid not wanting to burn up his gun, the OIC came over and told me he wants Cyclic rate, I just about said something about still having 6000+ rounds on my belt, but I fallowed orders, So once again as a smart MG I used semi-cyclic with barrel changes every 400-500 rounds, got stopped and yelled at to shoot everything up its time to go, so I told my AG to change the fire selection on the barrel to 950rpm (240B) on my next barrel change my rate of fire went from 750 to 950 and I burned through 5500~ish rounds the barrel got so hot it sagged when I let off the trigger, the OIC was happy, then later me and the LT had a talk with the CO about burning up $1000 usd chrome lined barrels.

My point is NO ONE TELLS YOU WHEN TO STOP SHOOTING, only when the Gun blows up or the gun dosen't function is it time to stop, and in the grim dark I see no reason for the Gun to stop you from shooting(machine spirit) cause of over heat, the nids surely will not care and your face will taste all the much better if you cant shoot.

IMO it should be,

"Brother, How many rounds do you have left?"
"A lot Brother what dose the Emperor ask of me?"
"I need to you Suppress that fortress tell our forces get to the wall do you understand"
"Understood **BoomboomboomBoomboomboomBoomboomboom**"
"Thanks Brother we are at the Objective, well done"
----not----
"Brother, How many rounds do you have left?"
"A lot Brother what dose the Emperor ask of me?"
"I need to you Suppress that fortress tell our forces get to the wall do you understand"
"Understood **Boomboomboom---pause Boomboomboom----Pause overheat**"
"Were is our covering suppressive fire"
"Sorry the Emperor dosen't think its fair that my gun fires so many bullets so he put a Over heat function in the gun'

As I say IMO.

Good write up, thanks.

Burst fire can still suppress and goes a long way towards keeping heat down. I guarantee you it will take more than 3 shots to make the weapon overheat.