Guardsman26 said:

30x113 mm would significantly reduce the total number of rounds carried for a given weight of ammunition.

So would 20x102mm.  A search found the following weights of 100 rds in steel ammo cans:

   12.7x99mm - 35 lbs

   20x102mm -- 92 lbs

   30x113mm - 110 lbs  (estimated weight -- a 30mm ammo can has 110 rds, and weighs 120 lbs)

Guardsman26 said:

Also, since 20x102 mm is closer in size to 12.7x99 mm HMG ammunition than 30x113 mm, you can carry more of it.

Actually, 20x102mm is much closer in size to 30x113mm, and steel ammo cans for the two are almost the same size, differing only in width. 

So, the amount you can carry is about the same for both 20mm and 30mm.  Want maximum ammo, minimum weight?  Stick with 12.7mm.

I think these days with prox fuzed ammo being available in 30x113 and the state of vehicle fire control systems you're better off with the slower but able to run the good fuses 30x113.

That little bit of extra MV just isn't that helpful in an era where your fcs can lay the gun as precisely as is standard now.

Also like Stan said, the difference in ammo carriage between 20x102 and 30x113  just isn't going to make up for the objectively less capable rounds.

It pains me to say any of this as someone who's emphatically not a fan of the m230lf but the truth is they've put together a really compelling package of capabilities that are extremely attractive.

This is why theres a very strong case for an improved .50 cal.

#polymer cased

#designed around APFSDS

#energies close to the russian 14.5mm

I read in a manual on urban warfare that Army testing found 20mm didn't penetrate much better than .50.

What about muzzle report / recoil? Is there a worthwhile difference between 20 and 30?

The projectile does the work, and straight (or near) straight walled cartridges give you the most projectile for the volume taken up by the ammunition, and then you have to consider if you go 20mm you'll likely want dual feed with a separate AP and HE round like the Germans do with their 20x139 Rh202 which further closes the gap with regards to ammunition weight and volume.

I see the 30x113 as having about the smallest useful HEDP, allowing you to roll with one ammunition type on a platform that's small and light enough (be it an M230, a critter like the ASP, or something else) to be a viable .50 / 40mm replacement on some platforms.  I do believe there's still a niche for something even smaller, I'm visualizing the same HEDP projectile as the 30x113, but with a shorter case, firing out of something XM307 sized, which would be less concussive and jarring on softskins while still having a flatter trajectory and lower TOF than the Mk19.

stancrist said:

So would 20x102mm.  A search found the following weights of 100 rds in steel ammo cans:    12.7x99mm - 35 lbs    20x102mm -- 92 lbs    30x113mm - 110 lbs  (estimated weight -- a 30mm ammo can has 110 rds, and weighs 120 lbs)

Kind of an interesting thing I learned recently in terms of 30x113 vs 20x102 - 30mm uses Aluminum cases (~70% lighter then brass) vs Brass for the 20mm.

So even though the 30mm has a shell weight ~2.5x larger, the 30mm is only marginally heavier than 20mm because of its AL case.

Refleks said:

I do believe there's still a niche for something even smaller, I'm visualizing the same HEDP projectile as the 30x113, but with a shorter case, firing out of something XM307 sized, which would be less concussive and jarring on softskins while still having a flatter trajectory and lower TOF than the Mk19.

I had actually thought resurrecting the WW2 German MK108 cannon would be a solid sweetspot between MK19 and M230LF.

40x53 = 790fps / 250g shell

30x90rb = 1700fps / 330g shell

You get a big boost in both velocity and HE payload vs 40mm, while still having a smaller / less blasty cannon then the m230lf.

Thing even looks like the MK19:

I have no measured data on either recoil levels or muzzle blast, so your guess is as good as mine.  

Farmplinker said:

I read in a manual on urban warfare that Army testing found 20mm didn't penetrate much better than .50.

Depends on which 20mm ammo you are comparing with which .50 cal.

The best 20x102 rounds for penetration will be the APDS developed for the naval Phalanx anti-missile system. The current MK244 as used in the Phalanx 1B looks interesting: it fires a 104.5g 14mm projectile at 1,100 m/s, from longer "optimised gun barrels".