Ollie's blog: The 6mm PPC-USA [feedly]

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Benchrest Loading Techniques Have Applications Afield, Too.

Dozens of different cartridges were used in the early years of competitive benchrest shooting, but when Remington introduced their .222 round in 1950 it started dominating almost immediately. The .222 and its variations pretty much ruled the sport until the 1970s, when the late Dr. Lou Palmisano and gunsmith Ferris Pindell modified the .220 Russian, a necked-down version of the 7.62×39 military round introduced by the Soviet Union during WWII.

The .220 Russian used a large rifle primer and had a tapered case with a 21-degree shoulder angle, but Palmisano and Pindell picked the case because the body matched the typical flame length of a small rifle primer. Along with changing the primer size, they "improved" the case for less body taper and a 30-degree neck.

The result was almost 0.2-inch shorter than the .222 Remington, but with enough extra powder room to boost velocities about 200 feet per second with the 52- or 53-grain match bullets usually used in benchrest shooting. Not only was the .22 PPC really accurate, but the increase in velocity resulted in a slight decrease in wind drift.

Some benchrest matches required a minimum bullet diameter of 6mm (0.243 inch), and soon the .22 PPC was necked up. The 6mm PPC proved just as accurate and many competitors started using it exclusively. By 1985 the 6mm PPC's popularity had increased to the point where Sako introduced commercial rifles and ammunition, designated 6mm PPC-USA. Today very few short-range benchrest competitors use anything else.

Many rifle shooters are fascinated by accuracy purely for accuracy's sake. In the 1990s I started using accuracy techniques for loading varmint ammo, and modifying factory rifles for the best accuracy. Eventually I ended up with a "tuned," heavy-barreled Remington 700 .223 Remington capable of 1/4-inch 5-shot groups at 100 yards.

Sadly, 1/4-inch groups aren't much in the benchrest world. I started thinking about ordering a custom rifle, but while dithering came across a used benchrest rifle built on a "sleeved" Remington 700 action on the consignment rack at Capital Sports & Western Wear in Helena, Montana. The scroll engraving on the barrel said "A. Erhardt," one of Capital's two in-house gunsmiths. Arnold wasn't in that day, but I knew he did excellent work, and the price was so low the rifle came home with me.

Turned Necks Only

The engraving on the other side of the barrel read "6PPC 262 nk," meaning the neck of the cases had to be turned down so loaded rounds had necks no more than 0.262-inch in diameter, rather than the maximum 0.265-inch of commercial ammo. Tight-fitting necks are standard practice in benchrest rifles, where everything fits together more precisely than on a production rifle. A cleaning rod with a tight patch around a nylon bore brush showed the rifling twist was 1:14 inches, average for 6mm PPC bench rifles, though some competitors use 13- or 15-inch twist barrels. The barrel was 25-1/2 inches long and just under an inch in diameter at the muzzle. (Arnold later told me he'd built the rifle for somebody else, using a Hart barrel. After sleeving the action in aluminum, he fitted a 2-ounce trigger and epoxied the sleeve into a synthetic stock.)

I had no interest in competing in benchrest matches, but wanted to test the accuracy of a rifle made solely for punching holes. It would also be used some on prairie dogs, though my usual preference is for much lighter rifles. The most suitable scope on hand was a 4.5-30×50 Bushnell Elite 6500. (A real benchrester would use a more powerful scope, often with the adjustments "frozen" mechanically.) With the Elite in Talley steel rings, the rifle weighs 13-1/2 pounds, the regulation limit for the "heavy varmint" class in benchrest shooting.

With Redding Competition dies and Norma brass with the necks turned in a Forster trimmer, loaded rounds had an average bullet run-out of 0.0005 inch, and 0.005 is considered decent for big-game ammo. A real benchrest shooter would use simpler and (perhaps) more precise tools, but for my purposes this seemed good enough.

On hand were a bunch of Berger target bullets. I decided to start with 65-grain bullets and Hodgdon Benchmark powder, primarily because I had most of an 8-pound jug on hand, and limited amounts of other powders.

Unlike conventional smokeless handloading, benchrest loading often starts with the bullet actually jammed into the rifling. This obviously won't do with a rifle used for prairie dog shooting, since hot barrels and jammed bullets create high pressures on warm days, and a round extracted without firing can leave the bullet stuck in the throat and powder spilled over the inside of the action. But "jammed" is the common place to start in bench loading, with the bullet seated slightly deeper for successive groups to see if accuracy improves. (This is safe, since in rifles pressures drop with deeper bullet seating.)

All the shooting was done with some BRT wind flags placed on the range, with the rifle on a Caldwell benchrest from MidwayUSA, since real accuracy testing is just about impossible without flags and a precise rest. My rifle proved to prefer the 65-grain Berger slightly jammed, and a powder charge slightly over the maximum listed by Hodgdon for 65-grain Hornady V-Max. (Apparently "max+" loads aren't uncommon in competitive shooting.) I next tried 62- and 68-grain Bergers, covering the common range used by bench shooters in the 6mm PPC, but found this rifle preferred the 65s, averaging five shots in 0.18 inch at 100 yards. Seated slightly deeper, the same bullet still shot accurately enough for rodent control that summer.

The next winter I tried other bullets, plus powders often used by benchrest competitors, including H322, IMR 8208 XBR and Accurate 2015. (The 2015 is made in Canada specifically for Western Powders, who purchased Accurate a few years ago, not the former 2015 made in the Czech Republic.) I wanted to try some Vihtavuori N133, the most popular 6mm PPC powder used by benchresters, but my testing took place during Obama Panic II. Any powder even vaguely suitable for the .223 Remington was in short supply, and no N133 could be found anywhere. I did have some slightly faster N130 on hand, so tried that instead.

The bullets were both target and varmint models, including some 66-grain handmade bullets specifically for benchrest shooting by Ronnie Cheek of Abilene, Texas. The Cheek bullets didn't shoot quite as well as the Bergers, perhaps because in my rifle their longer ogive couldn't reach the rifling, but I'll keep experimenting (I forgot to try Benchmark!). Happily, the 55-grain Nosler Ballistic Tip shot very well. It's a great varmint bullet, and at 3,500 fps was quite a bit zippier than the heavier bullets.

Nosler claims a 1:14-inch twist will stabilize their bullets up to the 80-grain Ballistic Tip, but my rifle wouldn't shoot anything over 70 grains worth a hoot. Maybe another rifle would, so I included some data for heavier bullets from both the Nosler and Berger manuals.
Most varmint shooters feel proud when their rifle groups five shots in a 1/2-inch at 100 yards. With a real benchrest rifle the standards are certainly different. With my 6mm PPC, 1/2-inch groups are kinda disappointing!
By John Barsness

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