"Use pressure rated pvc fittings (sch-40), not dwv or abs fittings." ~Benstern
Benstern, while your at it why don't you tell him to wipe his ass after he takes a sh*t? Talk about the basics...
As others have stated, it appears that possibly you intended to use bell reducers. Instead use a reducing bushing, as these allow longer socket depths on connections. I must note that for this issue in particular with bell reducer versus, bushing, wall thickness is not the issue, rather the shorter socket depths. Just thought Id point out as that is often times confused.
Just because everyone else seems to be taking the day off in the answering of your question, I decided to be so nice as to enter the data into GGDT! [If you are not aware of such software, Google the name "GGDT"]
Well I entered the given data into the program, the continued to screen shot the results. Listed are the two variation I tryed.
<a href="
http://www.spudfiles.com/uploader/uploa ... mental.GIF ">3' Chamber/ Barrel @ 60PSI</a>
<a href="
http://www.spudfiles.com/uploader/uploa ... ental1.GIF ">2' Chamber/ Barrel @ 60PSI</a>
Note: I very well could have botched any chance of accurate results with my horrible guesstimation on the projectile info.
The whole reducer deal. Well it doesn't matter which size your valve is, you could in theory go from 24" to the 1" threads for your valve. Although such would require more then one step. Also the step in availablity and price between 2", and 3" is rather noticeable. No worry though, 2" will suit the application just well.
As to the valve you intend to use, I have no prior experience with them. FrankRede seems to not had such a good experience with them, but I'm not sure it was out of the abuse of simply securing the chamber and barrel together, or something of that nature. I don't know how the threads by them selfs could just cause the male threads to 'snap'.