Thanks guy's, appreciate the comments, some pics from this weekends expo in a place called Larchamp, I borrowed a fellow club members Goldie as mines not ready yet:
Lee, I solder the brass using an oxy/propane set with a fine torch and use plumbers flux with electrical solder, the smaller brass square tube is 5.55mm external, the bigger stuff is 5.55mm internal, its a perfect fit inside. Its made by Albion Alloys and can be found on ebay.
Stu