Ken61,
My experience with this was in the shop of a German gunsmith friend, where we used standard tubes that came already contoured and turned to size. Also, I used reamers he had already selected to size and kept at his lathe. Consequently, I can't now recall the diameters, which were in mm, and for 16 ga. tubes anyway. Walther has a website, and on this site shows dimensions of the standard tubes they sell, you could use these for a guide. That part of the site, as I recall, is pretty hard to find( it might be in the German version of the site). I wouldn't try to install them with an interference fit, as suggested above. You would only have one chance to get it right, and would have a heck of a time getting them apart if you made a mistake. I put a barrel in an Anschutz action, that are intended for interference fit. Since it was for a wildcat, I threaded the action, so I could get the barrel out, if I had to. As it turned out, I had to remove the barrel, and wouldn't have been able to do it otherwise. If you make a slip fit, leaving a thousandth or so for solder, and tin both sides, you should be able to get the tubes out if necessary.
Good luck.
Mike
