Precision Case Neck Turning In A Lathe

Allow me to hark back to my own, long-term experience dealing with cartridge cases. My earlier work in this area was published in the 1966 Gun Digest as "Case Neck Variations… And Their Effect On Accuracy." Here I emphasized the importance the cartridge case plays in different types of shooting, ranging from common hunting rifles to bench rest matches.

I had detailed in the text howa "case neck gauge" that I had designed and built was used to efficiently measure case necks down to zero tolerance in just seconds or to discover dangerously-thick case necks that could cause increased chamber pressure. On the urging of John Amber, Gun Digest editor, these gauges were later manufactured and sold worldwide. I continue to use it today. Far At bottom, a Marquart factory-issue mandrel.

At top, a special modified mandrel as used in a Marquart neck turning tool with the longer main shaft to be used in lathe chuck. This mandrel also has a built-in case mouth stop (shown at pencil point) used to control case neck turning depth in lathe.

Adjustment wrenches are at bottom. Following my earlier experience with the cartridge case neck, I authored an article for Handloader’s Digest Ninth Edition (1981). Here I had made the comparison between reaming case necks and outside turning them. The work concluded, "Outside is Better." Pictured in the article was a special motor-driven, vertical minilathe that I had designed and built for the purpose of outside-turning case necks.

I make mention of this here to reiterate the importance that I had placed on the cartridge case Cases can be precision turned in just seconds following setup. Cases are fully stabilized on a spring-loaded spindle and conveniently rotated for precise measurement. neck, particularly when it involved extreme accuracy. Let’s move on to the fundamental details of a method of outside neck turning that I continue to use today.

In the process I use a modified conventional neck turning tool with an extended-length stepped mandrel held directly in the lathe chuck with the mandrel extended. Most of the commonly-used outside neck turning tools are basically similar by design. They consist of a rectangular aluminum body approximately two inches long x 1 3/8 inches wide and a half-inch thick. A cutout is made at center to accommodate the case neck and shoulder.

There is a hole into the cutout where the mandrel is held in line with the case neck. In the turning process, outside case neck metal is shaved from the case neck as it is manually rotated between the mandrel spindle and the cutting blade. If performed by hand it is a very lengthy, time-consuming process. I’ll show how it can be done in a lathe much more efficiently. Years ago I acquired a Marquart Neck Turning tool to be used with my modified neck turning mandrels.

While I used the same major shank size as the Marquart unit, I made up special stainless steel mandrels conforming to sized case neck shank diameter. The mandrels have a case mouth stop immediately beyond the caliber-specific diameter. The mandrel case neck stop diameter is held just under outside case neck thickness to prevent cutting-blade interference. The new, extended mandrel shaft body extends through and beyond the tool body about 5/8" and is held in the lathe chuck while neck turning.

Modified Neck Turning Tool Each caliber-specific mandrel is turned to size to fit just inside a newly sized case mouth close to bullet diameter. A minimal amount of tolerance here does not interfere with precise neck turning. While outside neck turning, the case head is held coaxially in the lathe tail stock chuck. The case neck is then moved into the rotating cutting blade, over the mandrel, until it reaches the stop.

Altering neck wall thickness is done by making shallow cuts and re-setting the cutter-blade until arriving at the desired neck thickness.

It has been a valuable tool in the accuracy handloading process where extreme accuracy is the goal. Far The same care in setup procedure is observed as the blade nears the neck-shoulder juncture by moving the case neck stop in or out of the main tool body closer or farther from the blade. All this is quite uncomplicated and cases can be outside neck sized in just seconds. My average turn-around time is 15-18 seconds for cases turned to under a thousandths runout. As I 5 Creedmoor cartridge.

These groups were fired in a totally-accurized Model 12 Savage Single Shot rifle with an 8-32 Sightron scope. Case necks were turned to zero thickness variation in producing these seven 100-yard groups as small as 0.094 MOA for a 0.268 MOA average. progress with the neck turning process I monitor thickness at intervals just to be sure all is well.

In the correct use of this method of outside neck turning, the increased neck wall thickening sometimes found at the neck shoulder juncture, commonly termed the doughnut, is conveniently removed. All that is required is to be sure the cutting blade on the neck turning tool cuts cleanly and fully just up to the case neckshoulder juncture. All this is quite uncomplicated.

Testing Outside Neck Turning Along with the other accuracy measures, it takes a great deal of planning to obviate the multitude of variables and possible accuracy-robbing deficiencies in a rifle. None the less, quality case necks and good bullet alignment area vital link in the ac- American Gunsmith Mailing List Policy Like many other publishers, we make portions of our customer list available to carefully screened companies that offer products and services we believe you may enjoy.

If you do not wish to receive these offers, and/or information, please let us know by contacting us at: American Gunsmith Opt-Out Program Norwalk, CT 06854 Please include your current mailing label. curacy chain that cannot be overlooked. I have developed a bulletcase alignment instrument whereby I can virtually predict the accuracy outcome of a rifle where case-bullet deficiencies area deciding issue.

It’s quite awakening to witness how the effects of a canted bullet engaging the rifling leade at an angle will enlarge an otherwise perfect group on target. Turning necks precisely helps reduce this greatly. AG