Correct me if I'm mistaken, but you failed to mention the model of rifle, the inner barrel you're using, and the type of endcap. You DO realize that it's impossible to answer you without you giving us any information at all? Two popular tanaka models are the M700 and the L96, with lots of modifications up to and including the Mantis rifle system. So..... ???
Sorry if this comes off as rude, even moreso if I'm simply not seeing an original post or something weird.