6mm PPC

6mm PPC

6mm PPC
Type Rifle / Competition
Place of origin USA
Production history
Designer Lou Palmisano / Ferris Pindell
Designed 1975
Specifications
Parent case .220 Russian
Case type Rimless, bottleneck
Bullet diameter .2430 in (6.17 mm)
Neck diameter .262 in (6.7 mm)
Shoulder diameter .431 in (10.9 mm)
Base diameter .441 in (11.2 mm)
Rim diameter .445 in (11.3 mm)
Case length 1.515 in (38.5 mm)
Overall length 2.100 in (53.3 mm)
Rifling twist 1-14"
Primer type Small rifle
Ballistic performance
Bullet weight/type Velocity Energy
60 gr (4 g) HP 3,300 ft/s (1,000 m/s) 1,452 ft·lbf (1,969 J)
70 gr (5 g) SX 3,250 ft/s (990 m/s) 1,641 ft·lbf (2,225 J)
Test barrel length: 24"
Source(s): Accurate Powder [1]

The 6mm PPC (Palmisano & Pindel Cartridge), or 6 PPC as it is more often called, is a centerfire rifle cartridge used almost exclusively for benchrest shooting.[2] At distances out to 300 yards, it is one of the most accurate cartridges available.[3][4] This cartridge's accuracy is produced by a combination of its stout posture, being only 1.23 inches (31 mm) long, and aggressive shoulder angle of 30 degrees compared to a 30-06's 17 degrees.[5]Today it is commonly used for railgun shooting matches and has been since the 1980's

Background

The cartridge is a necked-up version of the .22 PPC which is in turn based on a .220 Russian.[5] The standard bullet diameter for 6 mm caliber cartridges is .243 inches (6.2 mm), the same diameter used in the .243 Winchester and 6mm Remington cartridges. To obtain maximum accuracy, bullet weight and form are matched to the rifling twist rate of the barrel. Typically, 68-grain (4.4 g) bullets are used in barrels with twist rates of 1:13 (one twist for every 13" in the barrel), while 1:15 barrels can accommodate lighter 58-or-60-grain (3.8 or 3.9 g) accurately. The cartridge developed enough acceptance that rifles chambered for it are available commercially.[6]

Handloading

The parent cartridge for the 6PPC is the .220 Russian, which in turn derives from the 7.62×39mm. Brass can either be purchased, or formed from .220 Russian brass (7.62×39mm can also be used, but .220 Russian brass is usually higher quality and thickness, since it is designed to operate at higher pressures).

During the early development accuracy experts noted that perfectly concentric thickness of the cartridge neck were beneficial in lining up bullet to the bore - a feature mostly lacking in commercially available brass of the time. Most 6PPC chamber reamers are ground with a tight neck section that requires removing some case neck material ("turning the necks") to create a cartridge with a concentric fit and consistent neck-to-chamber clearances which contribute to the 6PPCs accuracy. While the SAAMI specification for neck thickness in a 6mm cartridge is usually .272 inches, it is common to see 6PPCs with .262, .268, or .269 custom neck sizes, hence modern factory ammunition is not commonly produced for the 6PPC as it would be dangerous to shoot in these custom chambers. To help clarify this, factory guns and ammunition are usually specified as the "6PPC-USA" cartridge which has a CIP/SAAMI specification. To the Note that a neck expanded, "unturned" (thickness of neck reduced) and loaded 220 Russian case neck will almost always be larger in diameter than the 6PPC rifle's chamber neck; if so, Method One does not apply—see Method Two. It is important to understand the characteristics of one's chamber before starting. Use of a "chamber cast" using Brownell's CERROSAFE® CHAMBER CASTING ALLOY or equivalent is a good way to accomplish this. Alternatively, one can use a manufacturer's print of the chamber (usually very hard to obtain, except for European manufacturers) or a print of the reamer used to cut the rifle chamber.

Cartridge Case Preparation Method One: The .223 inch (5.56 mm) neck of the .220 Russian is expanded to .243 inches (6 mm) using a mandrel, then the headspace is set using a full length sizing die for 6mm PPC. Next the case is trimmed, reloaded, and fire formed by firing the round in the chamber of a 6mm PPC rifle. The shoulder of the .220 Russian case is blown forward to 30 deg and the case walls are straightened, allowing for greater powder capacity. Competitors will also turn their case neck walls to a uniform given thickness, so that a fully loaded cartridge's neck diameter is just a few thousands of an inch less than that of the chamber's neck. Recently, Lapua, Norma and SAKO have begun making 6mm PPC brass.

Cartridge Case Preparation Method Two: Using the 220 Russian case, lubricate case and full length size in a 6PPC die with the expander button removed (it won't fit!) Insert a small PISTOL primer into the case to be converted (same size as small rifle primer.) Add a VERY STOUT quantity of a fast burning pistol propellant, such as Bullseye to the case—many other propellants will work, but it MUST be a fast burning pistol propellant. For this cartridge 16 grains of Bullseye works rather well. Melt some paraffin wax into the lid of a jar, and when it solidifies, turn the lid over and press it over the neck of the loaded blank cartridge, making a seal that will both keep the propellant in the case and provide a very modest resistance to the propellant when it is fired. Generously lubricate the case with "Imperial Sizing Die Wax" or some other VERY high quality case sizing lubricant (the serious benchrest shooters will only use Imperial.) Place the cartridge into the rifle and fire to "fireform" the case. The muzzle blast will be most impressive! Repeat for remaining cases, but don't allow barrel to overheat—if you can't hold the barrel in your hand, it is too hot, so slow down. When finished fireforming, clean rifle chamber to remove any hint of lubricant! Clean necks to remove lubricant and powder residue, then inside lubricate the necks with a Q Tip and Imperial Wax. Run cases thru a 6mm neck expander, which will be slightly oversized. Trim to length of 1.486" (this step may not be necessary.) Inside/outside chamfer the necks. Turn necks to a thickness that will allow, at BARE MINIMUM, 0.001" total clearance in the chamber for the loaded round (it helps to keep the neck turner in a pocket when not actually in use so that its temperature does not vary over the process; otherwise one can get considerable changes in the neck thickness due to heating and cooling of the "neck turner". Remember that we are working in increments of 0.0001" (ten thousandths of an inch) -- when one does the calculations, it is truly impressive how the dimensions of the neck turner can change over a 20 degree F range.) Lubricate the turner mandrel before each new case; again, Imperial is the optimal choice of lubricant. It is important when turning the necks to run the neck turner into the shoulder of the case a wee bit; if this is not done, one will experience the "Dreaded Doughnut" at the juncture of the neck to the rest of the case after the case is fired, and bullet seating can get very difficult. (Further, with a "doughnut", a loaded round with the projectile seated below doughnut can be larger in diameter than the chamber neck.) Lubricate the case again with Imperial wax. Full length size the case in a 6PPC die with the expander ball in place. Decap primer, clean primer pockets, remove case lube and you are now ready to TRULY LOAD the case.

As with other cartridges used in competition, precise handloading, a good rifle, and lots of practice make it possible to shoot very small consistent groups, with 5 or 10-shot groups with center-to-center measures of under 0.200 in (5.1 mm) at 200 yards (180 m).[7][8]

Other developments

As with many competition rounds, variations develop and the PPC family of cartridges has served as the foundation for many. In the native 22 and 6mm calibers, there are numerous improved versions both with a shorter body to reduce powder capacity and longer body to increase powder capacity.

In 1985 Birgir Runar Saemundsson from Iceland designed the 30 PPC, by necking up the standard 6 PPC to shoot 308 caliber bullets. Bullets at that time were 125 grain Bergers, which proved to be too heavy. The lighter bullets of 105 to 115 grains were needed. This caliber combination is very accurate for Bench Rest and Varmint for Score shooting.

In 1998 Arne Brennan conducted a theoretical study of calibers and cartridge cases and expanded the PPC family with the 6.5 PPC for the AR-15 rifle platform. As time evolved, the 6.5 PPC evolved into an improved case version like had been done for years with the 22 and 6 PPC. An improved 6.5 PPC variation branded the 6.5 Grendel was marketed by Alexander Arms LLC.[9] Others are the 6.5 CSS marketed by CompetitionShooting.com, the 6.5 PPCX developed by Arne Brennan and optimized for 100-108 grain 6.5mm bullets, and the 6.5 BPC developed by Jim Borden and Dr. Louis Palmisano and optimized for 81-88 grain flat base bullets. Brass for these improved versions of the 6.5 PPC cartridge is made by Lapua and Hornady.

In 2007, Mark Walker created the .30 Walker - a .30 caliber version of the improved PPC optimized for use with 110-118 grain flat base 30 caliber bullets. The .30 Walker was created for benchrest score shooting and has yielded impressive results with performance close to the .30 BR.[10]

In January 2010, Les Baer Custom discontinued offering the Alexander Arms 6.5 Grendel which is a trademarked brand and required an insurance commitment until Alexander Arms released its trademark in 2011, and announced the release of the .264 LBC-AR with brass manufactured by Hornady and ammunition loaded by Black Hills Ammunition. The .264 LBC-AR chamber is designed with a .295 neck like the 6.5 CSS and uses a 1 degree throat design like the 6.5 PPCX.

See also

Bibliography

References

  1. ↑ "6mm PPC data" (PDF). Accurate Powder.
  2. ↑ Simpson, Layne. "The 20th Century's Top Rifle Cartridge". Shooting Times.
  3. ↑ Schoby, Michael (2007). Hunter's Guide to Whitetail Rifles. Stackpole Books. p. 18. ISBN 978-0-8117-3359-5.
  4. ↑ Shideler, Dan (2010). Guns Illustrated 2011. Gun Digest Books. p. 140. ISBN 978-1-4402-1392-2. It's winning all its matches.
  5. 1 2 van Zwoll, Wayne (2003). Bolt Action Rifles. Krause Publications. p. 637. ISBN 978-0-87349-660-5.
  6. ↑ Walter, John (2006). Rifles of the World. Krause Publications. p. 414. ISBN 978-0-89689-241-5.
  7. ↑ "2005 IBS GROUP RECORDS". International Benchrest.
  8. ↑ Warner, Ken (1986). Gun Digest 1987. DBI Books. p. 234. ISBN 978-0-87349-001-6.
  9. ↑ Lewis, Jack (2007). The Gun Digest Book of Assault Weapons. Gun Digest Books. p. 77. ISBN 978-0-89689-498-3.
  10. ↑ Walker, Mark. "30 Walker". Retrieved 10 July 2013.

External links

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