you could watch couple of Mythbusters clips, they blow up lots of stuff with C4 so you can see what a real blasting cap etc looks like so you can imitate them more easily.
https://youtu.be/AwyniA5ryhY?t=14 and so on.
I think almost all action films have a C4 scene or two. the coiled wires and a timer with a display and a flashing light are cliches though so you may want to think if you want to use them in your film or not
close up of a blasting cap (detonator): https://youtu.be/01pjt_K-94M?t=2166
I think if you have an item which is closely looking like a blasting cap and just some white clay like substance it will sell the scene easily
Edited by aapo lettinen, 07 September 2015 - 05:17 AM.