ðə hˈɑːt ɡˈæsᵻz ɹᵻlˈiːst baɪ ðə bˈɜːnɪŋ ʌvðə pɹəpˈɛlənt ɹˈæpɪdli bˈɪld pɹˈɛʃɚ wɪðˌɪn ðə kˈɑːɹtɹɪdʒ, wˌɪtʃ pˈʊʃᵻz ˈiːðɚ dᵻɹˈɛktli ɔnðə hˈɛd ʌvðə fˈæsənɚ, ɔːɹ ˌɔn ɐ pˈɪstən, ɐksˈɛlɚɹˌeɪɾɪŋ ðə fˈæsənɚɹ ˌaʊɾəv ðə mˈʌzəl.
The hot gases released by the burning of the propellant rapidly build pressure within the cartridge, which pushes either directly on the head of the fastener, or on a piston, accelerating the fastener out of the muzzle.