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My uninformed opinion feels that a heavy machine gun (such as the KPVT up there) is the ideal choice. The way I see it, you're going to be using the coaxial for antinfantry work, and against other fairly soft targets. An HMG seems like it would give good performance against infantry, light vehicles, and the like, while not taking up so much space as something in the 20mm+ range. The M1919 and similar caliber weapons appear as though they don't have the armor penetration to reliably cheese things like M113s and early BMPs.

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I'd like to think that a 7.62 MG would be better than a heavier MG or an autocannon. Since the vehicle should have plenty of main gun rounds to sling, dealing with enemy AFVs should be done with that. The smaller caliber coax would allow for more ammo storage compared to the heavier MG rounds, and it would take up slightly less interior space. It also seems that most modern tanks have a 7.62 mm coax(coincidence? I think not!). A heavy machine gun could be valid, but I'd like a little more ammo. 

 

DTIC comparing 7.62 MGs-> Attribute Analysis of the Armor Machine Gun Candidates

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What's with the five round belts on the KPV-T?

At some early point in its development, abrams was supposed to have a 25mm autocannon coax.  Supposedly combat experience from the 1973 war showed that in the heat of combat, the crew inevitably shoots at anything tank-shaped with the main gun, even if it's a lesser vehicle like a BMP that could easily be swatted with an autocannon.

 

How this was determined, I have no idea, since so far as I can tell the tanks used on both sides had rifle-caliber MGs.

 

Soviet heavies IS-7, Ob 277, and Ob 770 had 14.5mm coax since 130mm ammo is gigantic and they didn't carry very much of it.  Also, the 14.5 doubled as a ranging MG, since it had reasonably close trajectory to the 130.

 

Tank coax strikes me as one of the few places where a blow-forward autocannon would really shine.

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Tank need to carry a lot of MG rounds simply because tankers use them much more, and i think reason for this is low effectiveness of MGs against infantry in cover. Especially in urban combat, 20-30 mm autocannons would have much better perfomance in those situation, which can decrease amount of 20-30 mm caliber ammo that tank need to carry. 

 

In fact T-14 model was showing some kind of autocannon, mounted on turret, which is indication of designers and army view on how next Russian MBT should be armed. 

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I wonder if one of the big reasons for tank coaxes being rifle-caliber, historically speaking, is that ammo is much easier to find than larger-caliber stuff.

That is one possibility. But in Russian army 30 mm shells are not hard to find either - BMP-2s and 3s, BTRs-80As/82s, MI-28s, Ka-52s, all use 30 mm rounds. Maybe thats why T-14 could be designed with 30 mm additional cannon.  

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Can imagine ammo boxes for them being far less of a pain in the ass to move new boxes to the gun and reload inside an AFV being a thing too.

 

Oh and, before I forget, more machinegun = better machinegun.

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Soviet heavies IS-7, Ob 277, and Ob 770 had 14.5mm coax since 130mm ammo is gigantic and they didn't carry very much of it.  Also, the 14.5 doubled as a ranging MG, since it had reasonably close trajectory to the 130.

 

 

The IS-7 also had two RP-46s in addition to the 14.5mm coax.

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Do the externally mounted autocannons even count as coaxial guns? I would have no objection to the mounting of such a weapon outside the turret while maintaining a smaller MG as the coaxial gun. 

There are some problems with such placement of autocannons - their recoil can create a force, that can turn a turret by some degree, screwing up accuracy. Question about vulnerability to artillery shells fragments, small arms fire, collisions with terrain are also serious for externally mounted weapons.

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There are some problems with such placement of autocannons - their recoil can create a force, that can turn a turret by some degree, screwing up accuracy. Question about vulnerability to artillery shells fragments, small arms fire, collisions with terrain are also serious for externally mounted weapons.

I did not know that recoil of an autocannon could be that impactful. All the others are sorta obvious risks, but I think you could expect minimal problems with good placement and armoring. 

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I did not know that recoil of an autocannon could be that impactful. All the others are sorta obvious risks, but I think you could expect minimal problems with good placement and armoring. 

2A42 30 mm autocannon, that is mounted on many Soviet/Russian vehicles, have recoil of 5 tons. 

 

Yes, but this mean that you need some kind of RCWS, which are bulky and usualy block commander view. 

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STRV-2000 in Act of Agression

 

e2kJ5oV.png

 

SWDN STRNG STRV STRNG   :P

 

Speaking about big coaxial guns.

kxvNBNc.jpg

 

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1mm691V.jpg

 

RY1EZrn.jpg

This is artist impression of T-14 MBT (Armata-based tank). Note 4 barrel HMG and 57 mm autocannon, mounted on unmanned turret. White tank is T-14 with 125 mm gun and dark is 152 mm MBT version/assault gun.

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I do still wonder if we will see a special coax on T-14 eventually. The 57 mm autocannon would certainly be interesting, especially for anti-personnel and structure usage.

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STRV-2000 in Act of Agression

 

e2kJ5oV.png

 

SWDN STRNG STRV STRNG   :P

 

The worst part about the STRV2000 in AoA is that it not only has the 140mm gun, it has a 140mm RAILGUN that somehow fires just fine without decapitating the tank everytime it fires, and perma stealth of course.

 

That things must have like, at least 4 trash can sized super reactors in that to power it or some shit.

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Another big reason you saw rifle caliber coax guns was space.

 

There were some oddities where a .50" was tried, but you always saw the fall back to something that did not take up much room, fired a lot of easily stowed cheap ammo that was common with your troops, and could chew up the squishies "good enough".

 

The old M37 variant of the M1919 was about as close to "ideal" as you got with a rifle caliber tank coax.

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MG-34 looks pretty good as a tank coax, IMO.  Sure, it's a bit sensitive to grit and crap, but it's in a tank so that's less pressing.  It has a barrel you can change from inside the tank without de-mounting the gun, and you don't need to headspace the barrel.

 

Also, unlike the M73, it works.

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MG-34 looks pretty good as a tank coax, IMO.  Sure, it's a bit sensitive to grit and crap, but it's in a tank so that's less pressing.  It has a barrel you can change from inside the tank without de-mounting the gun, and you don't need to headspace the barrel.

 

Also, unlike the M73, it works.

MG-34 is a pretty darn impressive piece of kit when you compare it to other machine guns in use in the mid 30's.  It's an actual real example of quality German engineering.  A bit expensive for wartime production maybe.  What say the firearms experts here?

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      ATTENTION DUELISTS:
      @Toxn
      @LostCosmonaut
      @Lord_James
      @DIADES
      @Datengineerwill
      @Whatismoo
      @Kal
      @Zadlo
      @Xoon
      detailed below is the expected format of the final submission.
      The date is set as Wednesday the 19th of June at 23:59 GMT.
      Again, incomplete designs may be submitted as they are and will be judged as seen fit.
       
      FINAL SUBMISSION:
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      [insert 3-projection (front, top, side) and isometric render of vehicle here)



      Table of basic statistics:

      Parameter

      Value

      Mass, combat


       
      Length, combat (transport)


       
      Width, combat (transport)


       
      Height, combat (transport)


       
      Ground Pressure, MMP (nominal)


       
      Estimated Speed


       
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      Crew, number (roles)


       
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      Secondary armament, caliber (ammo count ready/stowed)


       

       
      Vehicle designer’s notes: explain the thought process behind the design of the vehicle, ideas, and the development process from the designer’s point of view.

      Vehicle feature list:
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      1.     Link to Appendix 1- RFP spreadsheet, colored to reflect achieved performance.

      2.     Engine- type, displacement, rated power, cooling, neat features.

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      1.     Link to Appendix 1- RFP spreadsheet, colored to reflect achieved performance.

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      Fightability:

      1.     List vehicle features which improve its fightability and useability.

      Additonal Features:

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      Free expression zone: Let out your inner Thetan to fully impress the world with the fruit of your labor. Kindly spoiler this section if it’s very long.


       Example for filling in Appendix 1
    • By N-L-M
      Restricted: for Operating Thetan Eyes Only

      By order of Her Gracious and Serene Majesty Queen Diane Feinstein the VIII

      The Dianetic People’s Republic of California

      Anno Domini 2250

      SUBJ: RFP for new battle tank

      1.      Background.
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