[TML] 20mm cannons and bulky aliens

[Tod Glenn]

On Jan 22, 2008, at 4:24 PM, Bruce Johnson wrote:

>
> On Jan 22, 2008, at 2:26 PM, Brad Murray wrote:
>
>> I don't see any reason to
>> suspect that a sentient rhino out to kill other sentient rhinos would
>> have a compelling reason to carry a 20mm rifle when he could carry a
>> .300 H&H and sixteen times as much ammunition.
>
> two little letters:
>
> HE Ammo

In the case of explosive ammo, a conventional 20mm doesn't seem to  
make much sense.  You don't need high velocity if your KE is coming  
from an explosive warhead.  A 40mm grenade launcher has paltry recoil,  
is much lighter and had a nice bang on the receiving end.  Rifle  
grenades fill a similar niche.

Besides, Army studies of 20mm HE rounds showed they were pretty much  
useless for anti-personnel due to the lack of shrapnel mass.  That's  
why the original 20mm OICW was scrapped in favor of the XM-29 SABR  
with a 25mm projectile.

Even with high tech explosives, you still need fragmentation for  
lethality outside of immediate contact.  A bigger projectile gives you  
more and bigger splinters.  General consensus seems to be that 25-30mm  
projectiles are the ideal blend of size and lethality for infantry  
support weapons like GLs.

It's interesting that they took so long to figure this out, when the  
original SPIW project came to the same conclusion in the mid 1960s.