The Voyeur's Guide to Barrel Chambering - Part 3
by Germán A. Salazar and John Lowther
|Photo 16 - John Lowther|
There are various breech face styles, varying by action manufacturer and sometimes by the rifle's intended purpose. The Remington style with a recessed face that envelopes the bolt nose is very common and it provides excellent gas handling and safety in the event of a case rupture. However, feeding is not as smooth as with a coned breech face such as the Springfield 1903 and the original Winchester Model 70 used. A few actions call for a flat breech face, the RPA Quadlock is one example of this.
This project involves a BAT 3 lug action with a coned breech face; accordingly, our next step is cutting the cone and finalizing the tenon length to properly fit this action.
|Photo 17 - Cutter centered and ready|
|Photo 18 - Cutting the cone|
The first cut removes a tiny amount of metal near the bore. The next cut begins a little deeper and thus comes out a little further along the breech face.
Photo 18 shows the process after five or six passes. The cone angle is set by the angle of the cutter and remains fixed throughout the process.
There are coned reamers made now (think of a large deburring tool) but this is the old way and can be adapted to any cone angle. The BAT, for instance, calls for a 25 degree cone angle, whereas most other actions use a 30 degree cone.
|Photo 19 - Measuring the shoulder gap|
The tenon must be short enough to allow the receiver to screw on all the way without running into the locking lug abutments. However it must also be long enough to provide a close fit between the bolt nose and the cone, allowing just enough clearance to ensure proper functioning in all conditions (heat, cold, dust, etc.).
|Photo 20 - Finished and polished cone|
The finished cone should be smooth for good feeding characteristics. A little polishing with fine grit paper may be necessary once the cutting is done. No need to make a mirror out of it, but it shouldn't catch your fingernail as you run across the surface.
|Photo 21 - Visual check of bolt nose fit to the cone|
|Photo 22 - Front view of finished cone|
|Photo 23 - Action screwed onto the finished breech end of the barrel, but no chamber yet|
Click here for Part 4