Datum Measurement

The eloquent explanation regarding ammunition shortages provided by our editor in the September issue omitted a major factor. Before he descends upon me in a dark fury, I’ll explain. Every time Senators Feinstein, Shumer or The Golfer-in-Chief mention more "gun control" in seeking a cure for nutcase-inflicted mayhem, firearm production can’t keep up with the subsequent public demand, the sale of reloading equipment soars and the hoarding of related components begins.

If the Senators, et al., were wise enough they might realize they are all candidates for being handed Salesperson of the Year awards by every member of the National Shooting Sports Foundation. How embarrassing! But then, any desire for wisdom to suddenly emerge in Washington, DC is an exercise in futility. As this is written, new guns of all description, ammo, powder, bullets, primers and brass have all but disappeared from local retail inventories.

However, my sources tell me the industry is rapidly catching up with the surge in sales and the shortages are being overcome. I trust they will soon pass but I am certain they will return immediately after the next outburst from the ill-informed "auntie gunners." So will the hoarding. In my not-too-far-distant past days of competitive shooting, my Hamdenmade Hi-Standard Victor was putting out a brick of standard velocity .22LR every month.

The certainty a shortage would arise some unpredictable The caliper is not included. Bottom It is aligned with the chosen case diameter. Available from Forster but not shown is a blank disk with five starter holes to allow custom drilling of datum or bullet diameters not included in the kit. day and having no desire or funds to invest heavily in rimfire reloading equipment, I changed my habit of purchasing bricks of .22 ammunition to one of acquiring cases of it. Did I gouge them on price? No.

After applying my normal markup I charged the same as I had when .22LR was plentiful. How so, you ask? The cost of the ammo, even in case lots, had to rise because of the shortage, true, and sales volume increases more than made up the difference. Of course, I loaded my own centerfire ammunition after load testing at the club I’ve belonged to since 1977. As with .22LR, I purchased larger quantities of bullets, primers and brass, and did not gouge reloading customers seeking them.

They paid what they had always paid. A portion

These area good beginning. The dangerous consequences when excessive headspace is present are case stretching, case separation and gas leakage. of their price, equal to what I had paid for the requested items, was placed in an interest-bearing fund. It existed as the source from which all additional component purchases was drawn. The fund was never allowed to run dry. Admittedly, interest rates at savings institutions were higher then. My plan was long term, not immediate gain.

So I made another investment in some additional cramming up on reloading. This included books such as The Shooter’s Bible Guide to Rifle Ballistics, Designing and Forming Custom Cartridges for Rifles and Handguns by Dr. Ken Howell and Handloading by William C. Davis. Your choice of the many volumes mentioned in the later pages of Dr. Howell’s book and the official chamber specification drawings available from SAAMI (saami.org, Newtown, CT 06470) are valued contributors to your education.

The table of contents in Handloading alone gives you long list of sources. Here’s an abbreviated sample: Modern rifle and pistol bullets, gunpowder development, basic reloading operations, cartridge case troubleshooting, and how to make chamber casts. After all that comes a section on internal ballistic considerations for handloads. By the time you have mastered 50% of this, you will be considered the guru of gun gabbing for miles around holding a Ph D in handloading.

Recently, in addition to these books I made another investment. It’s anew tool from Forster Products, a familiar name to reloaders for their case conditioning system, case trimmers, Co-Ax presses, Bench Rest rifle dies, and among gunsmiths for tooling for over 60 years. Adding this tool to the Forster Universal Sight Mounting Fixture, screw assortment, and headspace gauges I already inventoried ought to make my Datum Dial Ammunition Measurement System feel right at home. Datum what?

The tool is versatile, easy to use and provides data to refine case sizing and bullet seating operations. I hear some of you asking, "That’s all very nice, Chick, but what ‘n where’s a ‘datum’?" A datum is a reference plane, point or diameter providing a base for other

measurements and calculations. In terms of cartridges, this indicates a relative measurement between the base of a fired case to a datum point established by SAAMI on its shoulder angle. This measurement must be taken from several cases fire formed in the same rifle firing identical loads and then averaged to establish the optimal headspace for that rifle’s chamber. The customer has to provide the fired cases. You may have, or want, to lend a hand taking and averaging these measurements.

Once the average is established, it represents the datum point for fired brass taken from a specific load in a specific rifle. Once established, a resizing die can be adjusted to consistently resize fired brass, thereby fine tuning it to match the chamber. The resized cases should be checked against the data produced by relative case measurement. The die adjustment should be checked periodically to assure it’s maintained.

Use an extra fine Sharpie indelible marker to note rifle, caliber and datum point on apiece of spare, spent brass for record keeping. As long as the measurements are sustained there should be no need for gauges to check headspace. For the reloader, it affords the opportunity to repeatedly produce ammunition custom tailored to the chamber of a specific firearm.

This tool can be used check consistency shared by a given manufacturer’s batch before seating operations, assist in establishing seating depth and taking measurements, including overall cartridge length. Unless a range is close to or included in your operation, the customer may have to jump in to establish seating depth of the bullet. In either case, this reveals how I’ve done it when into precision reloading for ultimate accuracy. A fired, unprimed case was used.

The bullet was inserted in the case mouth by hand to a depth leaving the ogive generously exposed. The end of the bullet was coated with and easilyremoved indicator and the dummy cartridge slowly chambered. Go very slowly until the bolt comes to a stop as a result of the bullet contacting the lands. Just as slowly, the case is extracted, overall length measured, the bullet removed, the case resized and primed, charged with powder, the bullet reseated, the OAL of the cartridge measured again, rechambered and fired.

Was the accuracy OK but could more or less leade improve it? Leade (pronounced leed) defines an open area located just forward of the chamber and slightly enlarged to make bullet entry into the bore easier. When fired, a bullet should move freely through the leade area prior to contact with the rifling. There’s somewhat of a debate twixt precision shooters. One group insists that allowing the bullet to barely touch the lands results in the best accuracy.

Another faction maintains more solid bullet contact with the rifling delivers more X-ring hits and takes more game. It has also been claimed too much leade could allow bullet wobble or other eccentric entry into the bore (while I’ve heard the claim, I have never heard how much leade is too much.) Which side your customer’s rifle favors has to be determined with multiple reloadings and test firing. The advice should be given before tests begin.

The cartridge must never be so long overall that the bullet becomes heavily engaged with the rifling. This can and has produced excessive chamber pressures. Some have been so excessive as to cause a brass case to rupture. I always favored the no-contact approach when loading for my pre-’64 Model 70 Winchester .30-06 bull-barreled match rifle, which now serves as the prize sniper rifle of the local SWAT Team (sigh.) I favored this approach for a simple reason: The rifle liked it the best.

I even won a few bench rest competitions with it. It’s unlikely this ammo and loading approach would perform as well in every other .30-06. Reloads and the guns in which they are tailored to serve make for happy marriages best left alone. All others, get in line. AG American Gunsmithing Association