soon to be a travel blogger who do video blog :)
If i were you and using sound samples I will find some machine guns samples and some single gun shots. and layer them up with so bassy low frequency (kick drum or sine wave)
the machine guns will be the main body of the sound. single shots as the top and attack. and the kick/bassy low freq will gives the bottom that banging sound.
after layered up you can tweak the level of three tracks and combine them together and add a bit a compression and reverb to blend the sounds more glued and natural.
hope this help :)