joestue wrote:personally i don't know how you can mix up the two numbers, ie 4000 and 200 or in my case 70-80.
You have to remember the audience of this forum. Many (most?) would know the difference, some would not.
joestue wrote:My point is: a safety factor of 3-5 is relatively safe, regardless of the material.
Yes, if you ignore dynamic loads and the derating for firing on a hot day. Lets see, IIRC 3" pressure rated PVC1120 is 220 PSIG at 73F. On a very hot day of 95F the derating is 0.68, so the 220 PSIG rating drops to 150 PSIG. A closed chamber propane + air gun will hit about 120 PSIG if the round jams in the barrel. So you are within 30 PSI of the rating of the pipe. Now figure the dynamic (shock) load, which in a standard propane + air gun probably isn't too severe, and you are into the pressure range where you are counting on the safety margin of the pipe. Engineers build things with safety margins for a reason and the reason isn't just because they are being anal.