Case Turning Fixture

Case rims, as used on some custom or wildcat cartridges, frequently require turning to fit the bolt face of a different rifle. Making a special fixture for this purpose is quite easily performed with a lathe and chambering reamer to fit the cartridge body taper. But it comes down to the gunsmith to get the job done.

Lathe Work For performing the in-line lathe work, the ideal body metal for making the rim turning fixture is a short section of barrel of same the caliber or around shaft large enough for an internal hole the size of the cartridge body being turned. With the rim turning fixture centered in a lathe chuck, use the proper cartridge reamer to form the chamber wall for the cartridge rims being turned. It need not include the entire length of the case body taper as long as it fits the cartridge taper.

When turning new case rims to size, it is important to eliminate 0010 inch difference in diameter, thereby requiring the larger rim to be turned down to properly fit the bolt face. It is necessary to advance the reamer beyond the case shoulder (datum line) for a good friction fit of the case while turning the rim. (Continued on page 21) The WSSM case rim measures 0.535 inches while the 7mm Rem Mag case measures 0.525 inches.

The larger case rim must be reduced in diameter to easily fit the smaller bolt face where a different bolt is used. the chamber shoulder, thereby allowing the new case to be held by body taper friction short of shoulder datum line contact. The shoulder and neck section of the case rim turning fixture can be bored out to eliminate shoulder bump. In this way, cases are held by light friction as they are aligned and turned. This works perfectly for both fired and unfired cases.

As an adjunct to body taper friction, I used a tapped brass screw through the body of the fixture as a means of contacting the web area of the case while turning. Contact of the screw is very light to avoid distortion of case. Turning Case Rims Cases can be precision turned, with the fixture precisely centered in the lathe, in less than 15 seconds as a

sharp, pre-set tool bit is advanced by the lathe carriage. It is best to use a carriage stop to avoid lathe bit contact with the case body as the rim cut is being completed. Be careful as the tool bit is being set to proper depth to turn the rims down. A cleanup is all that is normally required. A good example of a need for turning case rims down is when re-barreling for the Winchester Super Short Magnum cartridges.

The rim on these cases measures 0.535 inch, whereas standard case rim diameter on the 7mm and 300 Winchester Magnums is 0.525 inch. Bolt face for these cartridges are often a snug fit, causing sticky chambering and extraction. This is particularly true where the case rim is enclosed within the bolt face on bolts like the 700 Remington, et al. Conclusions There is no tool or fixture specifically for reducing case rim diameter currently being made. This easy-tomake tool does an excellent job and the cost is minimal.

The gunsmith shop is the best place to get the work done at a very modest cost. AG Far The lathe tool bit is seen in close proximity to the case rim, ready for turning. Cases can be removed with a screw-driver or padded pliers.