My friends and i have made about 7 guns, starting out with combustion ABS guns, and then we moved on to pnematic PVC guns. We have a 2" Sch40 PVC gun that we pressurize to about 100 PSI. We have been firing this gun for about a year and a half without any problems. However, I was recently chatting with the plumbing guy at home depot who was telling me PVC was unsafe for pressurized air (it also says this on the labels for PVC pipe fittings), and i was wondering if this is true. He told me over time the PVC breaks down from UV rays, cold temperatures, and constant air pressure, and eventually explodes.. Is there any truth to this? If so, how long before a PVC pnematic gun becomes 'unsafe'?