Thanks to both for answering. Let me see if and what I understood.
Todjaegeryou're saying that C4 may be more powerful than TNT but is also unstable and therefore not safe to use.Right?
No, not what I posted.
I will try to explain it another way.
C-4 or plastic explosives, is a solid mixture with a consistency similar to modeling clay which is quite stable, and is able to be easily molded (hence part of the name being plastic). The actual "active ingredient" in the explosive mixture, or otherwise the part which actually goes BANG, is the explosive RDX. Now RDX can also be quite stable, and provides a more energetic reaction than TNT and has been used as a component in explosive ordnance, but it is also more expensive.
IMO there would be no point in using something like C-4 in a warhead, because a warhead does not require that the explosive filler be able to be shaped or modeled, which are properties that C-4 after the binders are mixed with the explosive RDX.
Now TNT on the other hand, is an actual explosive just like RDX is, which starts out with a number of useful properties without requiring the addition of other compounds into a mixture. TNT itself is stable, and since it can be melted at a fairly low temperature (80 degrees C IIRC) allowing the resulting liquid to be easily poured into a variety of canisters, containers, molds, warheads, etc. This means that for the production of munitions, TNT works very well because it is easy to use, stable/predictable in behavior (meaning it will not go off when it should not, and will detonate when it should) and I suspect the cost of TNT is lower than a number of other explosives due to how long it has been around (~1860's).
TNT has started getting replaced for some roles in US service because there are newer explosive compounds which are 'better' for certain applications like HMX, or IMX-101, but something like C-4 would never really have been a realistic candidate for use in ordnance because of the properties it had.