Ammunition must be practical for its platform in order to be tactical. Small arms ammo must be practical for its platform which for most infantry is the foot soldier.
Cartridges which are too heavy are useless as are those which burn or explode when hit by projectiles or any external force.
One of the least known testing protocols is VULNERABILITY.
In this a human cadaver or suitable animal cadaver is fully outfitted with equipage and shot with a variety of projectiles , flame , dropped , crushed, blown up etc. in order to determine the VULNERABILITY of the ammunition to such factors on the battlefield. Ammunition is also left out in the weather to determine the VULNERABILTY to that and stored in a variety of climatic situations.
This type of testing was done mainly at Edgewood Arsenal,Md. (in the past-no current information available) and it was this type of testing which killed all of the era (1960s)combustible and semicombustible ammunition types.
Why? Being wounded is bad enough. Being wounded and ON FIRE due to your own ammunition stock is far worse.
These types of ammunition catch fire too easily in tactical situations according to VULNERABILITY testing.
The late ICCA(IAA) member Lyle Snider of Aberdeen,Md. did this testing for many years. Most of the extant examples of combustible small arms ammo in 5.56 AND 7.62 came from his collecting.
Some .223 combustibles from VULNERABILITY testing. PL mean PILOT LOT(first submitted lot).
These are combustible ball loads which have corroded due to chemical reaction.