I would also suggest thoroughly search the forums using the words stovepipe, stove pipe, smokestack and smoke stack. You'll get dozens of threads and should read them all. For example:
http://forum.lugerforum.com/showthre...ght=stove+pipe
http://luger.gunboards.com/showthrea...ght=stove+pipe
http://luger.gunboards.com/showthrea...ght=smokestack
The forums have a wealth of good information and most Luger problems have been discussed before. Good luck and let us know how it goes.