A CO<sub>2</sub> cylinder should be able to withstand the combustion pressure. DO NOT drill, cut, dent or modify the cylinder in any way or all bets are off. The only bummer is the very small exit hole at the top which will seriously limit the rate that gasses can flow out, and your ignition will have to stick in through that same hole to avoid drilling the cylinder. You could probably mount a 40' barrel to this thing to use up that relatively slow but huge volume of comustion gas. Although, the slow exit rate will probably allow the hot gasses to cool quite a bit, rapidly reducing the resultant pressure. You should definitely build this.