Modern marui pistols are much more robust than they used to be. While not designed for it they hold up well to use with propane.
The common stock parts that MAY break on you would be the slide or the nozzel. This however is nothing to really worry about since those parts only cost around $10 each and are both easy to swap out.
Last edited by Kozzie; October 4th, 2011 at 03:33..