Valve at barrel or chamber?

[theepicmool]

I've been lurking around and haven't seen this question addressed anywhere. Where is a better place for a sprinkler valve on a potato cannon: At the chamber like this: http://www.spudtech.com/images/products/500LP-1.jpg
Or at the barrel like this: http://www.duke.edu/~jwc13/images/tennis1.jpg

[jackssmirkingrevenge]

on the barrel, less dead space = better performance

[Floyd]

Put it on the barrel, it reduces dead space (which is bad) and ithe barrel blows up, it won't be right next to your shoulder.

[theepicmool]

thanks Its what i kind of suspected but I just found it strange that all the Spudgun Technology Center's cannons are with chamber located valves.