August 19, 2022
On a hunt on Kodiak Island last year, I experienced a case-head separation. I discovered the problem when I took the opportunity to try to shoot a red fox at 250 yards with the .338 Rem. Ultra Mag I was carrying. I missed with the first shot, and extraction was stiff, but I thought nothing of it since ice was caked on the rifle.
I dropped the fox with the third shot. Examining the three soot-blackened cartridge cases, I discovered two were ruptured nearly all the way around the case head, about a half-inch up from the rim. Clearly there was a problem, and having suspect handloads on Kodiak Island, where brown bear encounters are common, is not a good thing. When I got home I began my research. I knew my brass was of excellent quality. The cases in question had been loaded only three times. What had gone wrong?
Before loading the cases for my hunt on Kodiak Island, I’d trimmed them all to length and full-length resized them to ensure that they’d chamber easily. The rifle is a Winchester Model 70 customized by Lex Webernick of Rifle’s Inc. Its premium barrel has a chamber with standard dimensions because match-tight chambers can sometimes cause issues in the field. I began wondering if my handloads had been sized too much, pushing the shoulder back too far and creating excess headspace and overworking the brass.
Hornady recently introduced a cartridge headspace comparator kit, so I ordered one. Each kit comes with a red, anodized-aluminum base that brackets one jaw of your reloading caliper and clamps on via a small knurled brass thumbscrew. Five natural-colored aluminum bushings are included, and they cover cartridges from .17 caliber up to .35 caliber. A bushing chart on the back of the packaging indicates which bushings handle which cartridges. Sizes range from the “A” bushing, which is bored 0.330 inch, to the “E” bushing, which is bored 0.420 inch.
Made for comparing new brass, fired brass and resized brass, the comparator measures the distance from the cartridge case’s base to a contact point on the shoulder. Each bushing spans a spectrum of cartridges, but as long as the bushing’s inner rim contacts relatively near the middle portion of the case’s shoulder, it works as designed. The “E” bushing is appropriate for the .338 Rem. Ultra Mag. I clamped the bushing to my digital caliper and zeroed out the display. To set a baseline, I measured cases fired through my rifle’s chamber. Factory-ammo empties and handloaded empties measured exactly the same.
Then I measured one of the unfired handloads I had remaining after my trip to Kodiak Island. It measured .018 inch shorter than the fired cases. Here it’s worth pausing to discuss headspace. Benchrest shooters set the shoulder of fired cases back no more than .001 inch because ammo that fits without slop is more accurate. However, dirt or even dust on the cartridge shoulder can prevent the round from chambering. Hunters are best off sizing shoulders back .002 to .004. This ensures reliability and maintains good accuracy. Cases that are set back much more than .006 stretch a lot when fired. If that cycle is repeated, cases thin, become brittle and break just in front of the case head web. The shoulders on my .338 Ultra Mag reloads had three times that much setback. At least I was relieved that I’d found the source of the case-head separation problem. I measured some Barnes factory ammo I had on hand. It was .006 to .008 shorter than the fired cases, or .010 inch longer to the datum contact point on the shoulder than on the handloads I’d taken to Kodiak.
The Barnes factory ammo leaves plenty of headspace for reliability in my chamber, although probably a bit too much for long case life and maximum accuracy. Clearly, though, I’d resized my cases to create way too much headspace. I usually make a point of sizing cases just enough to chamber easily, but in this case, I’d had to switch loads at the last minute. In the interest of time and because I wanted full-length-sized cases sure to chamber easily, I used the simple but time-honored method of screwing the resizing die firmly down against the shell holder. I ran them through the rifle, and performance was stellar. Back to the garage I went, full-length resized the empties, and loaded them up again.
For hunting ammo, I usually set the sizing die to just bump the cartridge case shoulder back enough to allow the bolt handle to close comfortably. That achieves the snug .002 to .004 headspace beneficial to consistency and adequate for reliability. Clearly, I should have taken the time to do that in this case, but I got lazy and just spun the die down firmly against the shell holder. Theoretically, that should have been fine. But in this case perhaps my rifle’s chamber is a tad deep. More likely, my shell holder might be undersized. At any rate, the cartridge case shoulders were pushed back .018, which was .016 inch deeper than necessary to ensure reliability. And after repeatedly overworking the brass in this manner, the result was a case head separation.
The experience was a wake-up call. The good news is that for about $50 you can add Hornady’s headspace comparator kit to your toolbox. Use it to measure—and adjust—how much you are sizing cases. It takes only a few minutes to set up and only seconds to determine how much you are setting back the shoulder. It will help you create accurate ammo and, most importantly, reliable ammo.