The Voyeur's Guide to Barrel Chambering - Part 1
by Germán A. Salazar and John Lowther
A voyeur's guide to barrel chambering? Well, yes - this series isn't intended for anyone who owns a lathe; instead it is for those of us who send an action off to get a new barrel installed. Those who have the equipment know what to do and how to do it and I have nothing to teach them. On the other hand, if you've ever wondered just what goes into barrel fitting, this is it. We could have titled it: Everything You Always Wanted to Know About Barrel Chambering But Were Afraid to Ask - but that's kind of long for the index page.
The basic steps covered are threading, chambering and crowning the barrel blank. Each machinist who performs these operations has his preferences from among many possible ways to accomplish these tasks; what we'll show is John's way. If your man has a different approach, that's great, it's what works for him and this isn't intended to have you ask him to change his ways or to say that the way we show is the best or the only way; all it is, is one way - John's way.
|Photo 1 - BAT action with new barrel blank (above) and old barrel (below)|
|Photo 2 - Breech end of new Krieger barrel blank|
|Photo 3 - Barrel in the lathe|
|Photo 4 - Checking and minimizing runout at the muzzle end|
|Photo 5 - Indicating the breech end of the barrel|
The real work of indicating the barrel happens now. A long probe goes into the barrel, resting on the lands and grooves at least one inch in. The chuck is rotated by hand with an eye on the indicator. The chuck's jaws are adjusted to center the barrel perfectly in relation to the bore. This process can take quite a while, depending on the type of chuck used and the machinist's level of experience, but it is critical to a good final result. The reason that the probe is inserted at least one inch is to get it past the slight irregularities that exist right at the end of the bore. These are caused by the lapping tool reversing direction there during the barrel manufacturer's final lapping process.
|Photo 6 - Measuring the thread diameter on the old barrel|
|Photo 7 - First cutting pass begins|
The cutting tool removes a few thousandths of an inch of metal at most, so many passes are required to reduce the tenon diameter to the desired end size.
|Photo 8 - Barrel tenon at final diameter before threading|
Click here for Part 2