August 19, 2019
Lead photo by Michael Anschuetz
Necking down cartridge cases for bullets of smaller diameters has been going on for a very long time. During the 1920s, wildcatters squeezed down 7x57mm Mauser and 30-06 Springfield cases for .25-caliber bullets and produced cartridges known today as the 257 Roberts and 25-06 Remington. Those are but two of many similar stories, and the 6mm Creedmoor is the latest. Its birth became known soon after Hornady’s 2008 introduction of the 6.5 Creedmoor for Across the Course competition. At that time the 6x47 Lapua, 6mm BR Norma, 6XC Tubb, 6mm Dasher, and 243 Winchester had become quite popular for long-distance competitive shooting, and within a few years the 6mm Creedmoor wildcat, made by necking down the 6.5 Creedmoor case, ranked among the most popular cartridges used in Precision Rifle Series (PRS) competition.
For those who are not familiar with PRS, it is a points-awarded series of practical/tactical/sniper-style matches held across the country each year. Rather than shooting from a benchrest, competitors are timed as they race through a number of stages while shooting under simulated field conditions. Various types of rests, such as bags, bipods, boulders, logs, and barricades, are used. Shooting positions range from comfortable to awkward, with some stages requiring weak-shoulder or offhand shooting. Targets vary from golf balls hanging on strings at 150 yards to steel targets across a canyon at over 1,200 yards. It is very much like IPSC open-class competition, but rather than using high-capacity handguns, long-range rifles are used. At the end of each year the scores from 15 different matches are combined, and the top 50 shooters are invited to compete in the PRS Finale Match.
The 6mm Creedmoor wildcat caught on fast. As posted by Cal Zant in his PrecisionRifleBlog.com, just over half of the competitors who qualified to shoot Open Division during the Finale Match of 2013 used 6mm cartridges, with the 6mm Creedmoor and 6x47 Lapua tied for first place in popularity. Close behind in the third and fourth spots were the 6XC and the 243 Winchester.
The 6mm Creedmoor is still winning matches as you read this, and due to its S.A.A.M.I. registration by Hornady, it has shed its wildcat status. Maximum average chamber pressure was set at 62,000 psi. The 108-grain ELD Match at 2,960 fps and Precision Hunter with the 103-grain ELD-X at 3,050 fps are the first two loads to be introduced by Hornady. Both velocity ratings are from a 24-inch pressure barrel. Additional loads are in the works.
Ruger was first to produce rifles in 6mm Creedmoor. The company’s Precision Rifle has a 24-inch barrel, and the one I am shooting weighs close to 15 pounds with a 3.5-21X Bushnell Elite Tactical DMR II-i scope. The Predator version of Ruger’s American Hunter rifle has a lighter 22-inch barrel and weighs just over 8.5 pounds with a 4-16X Nikon Monarch scope. The barrels of both rifles have a 1:7.7 rifling twist rate.
I found the 6mm Creedmoor to be falling-off-a-log easy to handload with no sudden pressure spikes as maximum-pressure loads were approached. Suitable primers, cases, powders, and bullets are abundant. As I write this, Hornady is the only company offering unprimed cases with the 6mm Creedmoor headstamp, but 6.5 Creedmoor cases from that company as well as Lapua, Nosler, and Starline are easily necked down for 0.243-inch bullets. The Redding Series C full-length resizing die on my reloading bench worked perfectly.
Like its 6.5x47 case, Lapua’s 6.5mm Creedmoor case uses a Small Rifle primer, and it has a 1.5mm (0.059-inch) flash hole. Lapua brass is extremely uniform in weight, and many competitors use it because its great hardness yields long case life. Hornady and Nosler cases use Large Rifle primers, and both have standard S.A.A.M.I. flash hole diameters of 0.074 to 0.078 inch. Starline cases are available with Small Rifle or Large Rifle primer pockets, both with the same flash hole diameter as Hornady and Nosler cases. When handloading the Lapua case, keep in mind that the standard 0.070-inch-diameter decapping pin is too large for its flash hole. The 0.058-inch pin in Redding dies for both Creedmoor cartridges works with both flash hole diameters.
Due to the availability of many suitable powders, singling out a favorite for the 6mm Creedmoor will require a lot more shooting than I have done. The first 6.5 Creedmoor factory loads introduced by Hornady back in 2008 were loaded with 120- and 140-grain A-Max bullets. Printed on their boxes were recommended powders and charge weights of 39.0 grains of Varget for the former bullet and 41.5 grains of H4350 for the latter. Nine years later, H4350 is still a favorite not only among precision shooters who handload that cartridge, but also among those who are shooting the 6mm Creedmoor as well. Other Hodgdon powders have the correct burn rates, and Hybrid 100V, H4831SC, IMR 4350, and IMR 4451 appear to be the most popular among those who are shooting the 6mm Creedmoor in competition. For Berger’s 115-grain VLD Target bullet, I found H1000 and IMR 7977 also to be excellent choices. Superformance proved to be equally good behind the Berger 115-grain VLD Hunting.
6mm Creedmoor Case Considerations
One of the first lessons eventually learned by precision shooters is the importance of cartridge concentricity. When cartridges with case neck wall thickness variations (thicker on one side than the other) are chambered, misalignment between the axis of the bullet and the axes of the case and the bore of the barrel are introduced. When loading for a precision rifle, one of the goals is to make each cartridge as concentric as possible, and eliminating neck wall thickness variations goes a long way toward accomplishing that.
I used a Hornady Neck Turn Tool powered by the electric drill from that company’s Case Prep Duo kit. The cutter blade was adjusted to shave brass only from the thick side of the neck. All cases were then run through a Redding Type S bushing-style neck sizing die with a bushing 0.002 inch smaller than the neck diameter of a loaded round. When cartridge neck spring-back decreased from repeated firings, a bushing 0.003 inch smaller than cartridge neck diameter was used. A Hornady Lock-N-Load Power Case Prep Center trimmed virgin cases to a uniform length, followed by chamfering and deburring. That was repeated after four firings.
For the Precision Rifle, I continued to neck size only, and after several firings, the fit of some cases became too tight for easy bolt closure. A Redding body die was used to bump back the shoulder of a case the precise amount without resizing its body. The Ruger American is a hunting rifle, so its cases were full-length resized with a Redding bushing-style die. When seating bullets for both rifles, a Redding Competition die was used.
Some stages in PRS competition require 30 shots or more with little to no time allowed for barrel cool-down, so when accuracy-testing loads in the Precision Rifle, I went with four, five-shot groups with the barrel cooled by running water through its bore between each 20-shot string. That was followed by four dry patches through the bore with one fouling shot fired prior to shooting the next series of groups. When shooting the Ruger American, the number of shots per group was reduced to three, and since big-game rifles are seldom subjected to lengthy strings of sustained firing, its barrel was cooled down between each six-shot string.
A Hornady Overall Length Gauge revealed slight differences in chamber throat length in the two rifles. The dimension from case head (or boltface) to the point on the ogive of a bullet that contacts the rifling was 2.160 inches for the Precision Rifle and 2.185 inches for the American Rifle. With bullets seated to the same overall cartridge length for the two rifles, free-travel prior to rifling engagement was 0.025 inch longer in the American Rifle. The amount of jump for various handloads is shown in the accompanying chart.
6mm Creedmoor vs. 243 Winchester
While the 6.5 Creedmoor has made great strides in competitive sports, it has achieved even more success among hunters. The 6mm Creedmoor story may eventually read the same except for the fact that in addition to being an excellent choice for use on deer-size game, it is better suited for varmint shooting than its 6.5mm parent. The 243 Winchester has long been our most popular dual-purpose cartridge of its caliber, and hunters are already choosing sides in a 243 Winchester versus 6mm Creedmoor debate. I might as well chime in.
Choosing between the two cartridges boils down to nothing more complicated than what the rifle will be used for and which bullets will be used. If it is for long-distance competitive shooting, there is no clear winner between the two cartridges. If it is for use on deer, similar accuracy and velocities of the two cartridges make one as good as the other.
And how, you might be asking, can the 6mm Creedmoor equal the larger 243 Winchester in velocity? Appearances are deceiving. When once-fired (and not resized) Hornady cases are filled to the brim with water, the 243 Winchester holds 55.2 grains versus 52.6 grains for the 6mm Creedmoor. That’s a difference of only 2.6 grains. From head to beginning of shoulder, the 243 case is a bit longer, but the Creedmoor case makes up part of the difference in gross capacity by having slightly less body taper, a sharper shoulder angle, and a longer neck.
Next question. If the capacity of the 243 Winchester is a bit greater than the 6mm Creedmoor, why are some of the maximum charge weights listed in the 2018 Annual Manual heavier and velocities higher for the 6mm Creedmoor? For one, S.A.A.M.I. maximum chamber pressure for the 6mm Creedmoor is a bit higher, and that may account for some of the difference. But most of the difference is due to the net capacities of the two cases when both are loaded to their S.A.A.M.I. maximum overall lengths.
When developing the 308 Winchester back in the 1950s, Winchester technicians gave the new cartridge a maximum cartridge length of 2.810 inches. But when necking down the 308 case for 0.243-inch bullets, they shortened overall length to 2.710 inches. It was a grand plan for short, varmint-weight bullets, but when longer 100-grain bullets are seated to that length, they displace powder capacity and combustion area by extending deep into the case. Factory-loaded 243 ammo is kept within the established maximum overall length, and the same holds true for those who develop load data for various reloading manuals. But since the longer chamber throat and magazine lengths of some rifles will accept longer cartridge lengths, handloaders have never been restricted by the S.A.A.M.I. maximum length.
Interior magazine length of many rifles is plenty roomy for seating bullets longer, with my Pre-’64 Model 70 in 243 Winchester measuring 3.125 inches. The magazine of the Remington Model 700 short action is 2.840 inches, and the two Ruger rifles featured in this report also have magazine lengths of 2.840 inches. Chamber throats for 243 Winchester rifles do vary in length, but they are usually long enough to seat bullets beyond the S.A.A.M.I. maximum. When Hornady’s new 103-grain ELD-X is seated to an overall length of 2.820 inches, it free-travels 0.024 inch prior to engaging the rifling in my Model 70. Due to the shorter throat of my Remington Model 700, bullet jump in it is reduced to 0.007 inch.
While the two cartridges have the potential of being handloaded to virtually the same velocities, the pendulum swings back in favor of the 6mm Creedmoor for the hunter who wishes to bump off a deer with one of the new breed of finger-long bullets from a factory rifle. Rifling twist rate for most 243 Winchester rifles is 1:10 inches, and that’s too slow to stabilize pointed bullets much longer than 1.150 inches. Respective lengths of the 115-grain Berger Match Grade VLD Hunting and the 103-grain Hornady ELD-X are 1.346 and 1.262 inches. Regardless of the cartridge used, Berger recommends a twist no slower than 1:7 for its 115-grain bullet, and Hornady says no slower than 1:8 for its 103-grain bullet.
I will add that bullet manufacturers are sometimes a bit conservative when making rifling twist rate recommendations, and the accuracy of the two 115-grain Bergers from the 1:7.7 twist of the Ruger test rifles is an example. Perfectly round holes in test targets revealed the Target and Hunting versions of that bullet to be adequately stabilized by the slower twist of those rifles. The 110-grain Sierra MatchKing is the same length as the Berger bullets, and it too was stabilized by the 1:7.7 twist. But my longest targets were at 300 yards, and stability may begin to deteriorate at longer distances unless a quicker twist rate is used. When I mentioned the accuracy I was getting with the 110-grain MatchKing to one of the technical guys at Sierra, he stated that several other shooters had reported the same level of accuracy with 1:8-twist barrels, but none of them had shot the bullet at great distances. He added that competitors who intend to use that bullet at 500 yards and beyond should hedge their bets by using a 1:7 twist.
When it comes to choosing the proper rifling twist rate for a particular bullet, its length matters more than its weight. The 100-grain Sierra SBT GameKing, for example, is adequately stabilized by the 1:10 twist of a rifle in 243 Winchester. It is only 3 percent lighter than Hornady’s 103-grain ELD-X, but the longer ogive profile of the Hornady bullet makes it almost 18 percent longer overall, and that makes it incompatible with a 1:10 twist. The longer Berger and Hornady bullets will work in the 243 Winchester, but only if the rifle has a custom barrel with a twist rate quick enough to stabilize them in flight. As factory rifles suitable for use with extra-long 0.243-inch bullets go, the 6mm Creedmoor will continue to be the only choice unless Nosler decides to follow the currently available quick-twist Model 48 rifle in 22-250 with a quick-twist 243 Winchester.
Continuing on with factory rifles with standard S.A.A.M.I. chamber dimensions, the 243 Winchester is a better choice for use on both varmints and deer because the shorter chamber throats of rifles in that caliber make them more suitable for use with short, varmint-weight bullets. The lightweights can be used in the Creedmoor, but when seated one bullet diameter deep into the neck of the case, they have to travel quite a long distance before reaching the rifling. While lead-core bullets are usually more accurate with less free-travel, you might get lucky as I did with the 70-grain Sierra MatchKing and find an exception that works.
I have been a fan of various 6mm rifle cartridges for quite a long time, I have taken a number of deer and pronghorn antelopes with the 243 Winchester, 6mm/244 Remington, 6mm-284, and 6mm-06. In addition to being quite accurate, all of those cartridges are easy on the shoulder and deadly on deer and other game of that size to boot. The 6mm Creedmoor is the newest member of a wonderful family of cartridges, and it should make its mark in the hunting fields, just as it has in competitive shooting.