Inside neck reaming improves firearms
When handloading was gaining popularity in the early 1950s, most reloaders didn't have too much technical data to rely on. Much of what was done was simple trial and error, or using data and procedures received from another handloader.
Reloading equipment was basic, consisting of a press, scale, powder measure and mouth chambering tool. When problems arose, there was no easy way to find what went wrong.
One major problem that worried handloaders was neck splits. It was generally accepted that neck splitting was the result of too many firings or excessive powder charges.
I suppose it's fair to say that each of these might be a factor in neck splitting, but we know now that case necks crack from excessive resizing and possibly an oversize neck area in the chamber. Also, case necks aren't exactly round when manufactured or concentric (known as case run-out) to the case body. In other words, during the drawing process, a neck can end up with more metal on one side. It can also be out of alignment, so to speak.
We were aware that neck metal thickens from firing, and we also thought that inside neck reaming was the answer. Actually, inside neck reaming doesn't correct the neck that has more metal on one side. The reamer removes an equal amount of inside metal from all sides of the neck. This still leaves more metal on one side.
The answer is to remove the metal (high spots) from the outside of the neck. By doing this properly, the neck case wall will be the same thickness the entire way around the neck.
I mentioned that the center of the neck can be out of alignment with the center of the case. New brass neck run-out usually can be corrected by running the case in a full-ength resizing die. If a case shows run-out after it's fired, the problem is in the chamber.
The neck portion of that chamber is either out of round -- not concentric with the chamber body -- or large enough to allow the case neck to expand more on one side than the other. This is no real problem with big-game rifles, but top-notch varmint rigs should be re-chambered.
The K&M Neck Turner is easy to use and not too difficult to set up. lt consists of a screwdriver-type handle, a shell holder assembly that uses Lee shell holders and a separate cutting tool. An empty case is placed in the correct Lee shell holder, and a loader should hold the shell holder assembly in one hand while turning the tool's handle clockwise until a plunger in the handle bears firmly against the bottom of the shell case. The empty case is flush in the Lee shell holder and cannot move.
The cutter is an "E" shaped device that incorporates a pilot and adjustable cutting knife. Pilots come in caliber sizes such as .224, 6mm, .308, etc. The correct diameter pilot must be used for the case being turned. It's best to thoroughly clean the inside of the case mouth and also lightly lube the pilot.
Loosen the knife holding screw with an Alien wrench, and turn the cutting adjustment screw counterclockwise until the case mouth will slip under the knife. Insert the case mouth over pilot and turn the adjustment screw clockwise until the knife just touches the case neck. Remove the case and tighten the screw.
Slip the case mouth over the pilot and turn the shell clockwise while pushing the neck into the cutter. The cutter may not make a clean cut the entire way around the neck, as it removes high spots. However, as the cutter moves toward the case shoulder, it's very Iikely that metal will be removed the complete way around.
Continue to make cutter adjustments until the desired wall thickness is obtained. Don't overdo it. Make shallow cuts. The cutter can be adjusted to remove as little as 0.0002 (two ten-thousandths of an inch).
Recently, RCBS came out with an outside neck turning tool. It's basically a Trim Pro case trimmer with a special outside neck cutting tool. It is manually operated. The one I tested did a superb job.