bobsaget wrote:If i am molding a piston out of the connector that the piston will slide in, i will need to make a slight equalization hole because the piston is the same exact size as the gun itself, correct? And how large should my equalization hole be if the piston is 3/4 in wide or about two CM. I am planning on making a very small hole and making it larger untill the piston moves back. The piston should move back if i have a very small hole right, something around 2 mm?
You don't need an equalization hole unless you seal the piston using o-rings. Even if it looks like a tight fit, air will flow through quite easily.
mrsteel wrote:im building a piston valve airgun and i want to know if the diameter of the exhaust port should be bigger or smaller than that of the barrel, whichone woold give more power to the barrel?
It shouldn't need to be as large as the barrel in large bore guns, but in small bore guns it should be larger. For most small bore guns with small pistons (anything up to 3/4"), a blowgun should work if the piston is built well. But you will be hindering performance, I always recommend using 1/4" ball valves as they do improve performance quite noticeably in most cases. When it comes to exhaust valves, bigger is always better (in correlation with speed).