Making a Barrel Chamber Neck and Leade Section

As I was cutting a short section of muzzle from a target rifle barrel, an idea struck me. Why not run the chamber reamer into this short piece as a convenient way to check the chamber neck and throat section of the barrel? There would never be a better opportunity to see the chamber neck close up, which is often an area of question with gunsmiths. As a longtime accuracy handloader, I saw a need for this reproduction of the chamber neck and leade here, too.

The closer the case neck diameter is to chamber neck diameter, the better it is for accuracy during load workup. When the overall case tolerance is close and bullet alignment with the case neck is truly coaxial, a favorable condition exists. Further, as neck walls thicken during repeated firing, the case-neck-to-chamber-neck tolerance may be diminished. This can create a restricted bullet-pull from the case mouth, resulting in a dangerous condition as pressures rise.

This is particularly true where maximum or nearmaximum handloads are used. The Right top: Shown here are short barrel chambers along with the reamers used to make them. From the top, the cartridges are the 5mm/ 35 SMc and the 6mm PPC. These short chambers can be made to fit any cartridge.

Right bottom: Here a short barrel section is in the lathe chuck being reamed for the 5mm/35 SMc cartridge. error is further compounded if the bullet is seated to touch the lands, preventing free travel of the bullet as it enters the chamber leade. All this can be checked with the duplicate chamber neck tool. Chambering the short piece of barrel cutoff can be performed with the piece centered in a lathe chuck.

It’s only necessary to cut the chamber until the case datum line makes contact, thereby establishing a limit to case entry into the partially cut chamber. In this way, the critical points can

Properly stamped, each shows cartridge identification as well as neck diameter. Far Determining proper bullet-seating depth becomes an easy procedure in this way. be closely examined with a magnifying glass. This includes the area of case shoulder contact, and the entire chamber neck and rifling leade (throat). The finished part should be properly labeled for the individual cartridge being used.

In the bullet-seating process, the duplicate chamber-neck section can A special chamberneck gauge designed by author is used to accurately measure case-neck diameter. conveniently be used in the important role as proper seating depth is being established. As a bullet is being tested for seating depth, it can be left long and tested for bullet/rifling engraving as the case is inserted into the chamber neck.

This is a very handy procedure using the short neck-leade section of the barrel to establish the important overall length of a cartridge. Monitoring the case-neck wall thickness and overall loaded-case neck diameter is equally important to your customers who are handloaders. This condition can be checked in seconds by inserting the loaded round into the chambered, short section. This amounts to double the case-neck wall thickness added to bullet diameter.

Thus you will know immediately when and to what degree case necks need to be turned. Conclusions Making up a duplicate, short section of the chamber neck and leade will result in a most useful tool for the rifleman/handloader who stands to benefit in many ways through its use. Thus, the cost and time involved to make the chamber neck and leade section is well worth the effort. I