6mm PPC

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 meters, 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 31 mm (1.22 in) 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 1980s.

6mm PPC
6mm PPC
TypeRifle / Competition
Place of originUSA
Production history
DesignerLou Palmisano / Ferris Pindell
Designed1975
Specifications
Parent case.220 Russian (5.6×39mm)
Case typeRimless, 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 length1.515 in (38.5 mm)
Overall length2.100 in (53.3 mm)
Rifling twist1-14"
Primer typeSmall rifle
Ballistic performance
Bullet mass/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]

Background

The cartridge is a necked-up version of the .22 PPC which is in turn based on a .220 Russian (5.6×39mm).[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 gr (4.41 g) bullets are used in barrels with twist rates of 1 in 13 inch (1 in 330 mm), while 1 in 15 inch (1 in 380 mm) barrel twists can accommodate lighter 58 or 60 gr (3.76 or 3.89 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 (5.6×39mm), 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 its early development, accuracy experts noted that perfectly concentric thicknesses 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 6PPC's accuracy. While the SAAMI specification for neck thickness in a 6mm cartridge is usually .272 inches (6.91 mm), 6PPCs with .262 inches (6.65 mm), .268 inches (6.81 mm), or .269 inches (6.83 mm) custom neck sizes are commonly seen, 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 mentioned below does not apply—see Method Two. It is important to understand the characteristics of one's chamber before starting, which can be checked with a tool such as a "chamber cast" (for example Brownell's CERROSAFE® CHAMBER CASTING ALLOY). Alternatively, one can use a manufacturer's print of the chamber (usually very hard to obtain, except for European rifle 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. This way the shoulder of the .220 Russian case have become blown forward to 30 deg and the case walls have been straightened, allowing for greater powder capacity. Competitors will also turn the neck walls of their case to a uniform given thickness, so that a fully loaded cartridge's neck diameter is just a few hundredths of a millimeter (or thousandths of an inch) less than that of the chamber's neck. Recently, European cartridge manufacturers Lapua, Norma and SAKO have begun making 6mm PPC brass.
Cartridge Case Preparation Method Two
Starting with a .220 Russian case to be turned into a blank cartridge for fireforming. First the case is lubricated and full length sized in a 6PPC die with the expander button removed (since the die will not fit otherwise). A small pistol primer is then inserted into the case to be converted. (While the small pistol primer has the same size as small rifle primer, they have different pressure ratings). A very large quantity of fast burning pistol propellant is then added to the case. It is of very high importance that the propellant is of a fast burning type. For this cartridge, some have reported 16 grains (1.04 g) of Bullseye® powder working well. Some paraffin wax is then melted into the lid of a jar or something similar, and when it solidifies, the lid is turned over, pressing it over the neck of the now 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. The case is then generously lubricated with a high quality case sizing lubricant, of which Imperial Sizing Die Wax is a popular variant. The cartridge is then placed into the rifle and fired to get what is called a "fireformed case". Fireforming in general gives a very large muzzle blast. As overheating can shorten the life of the barrel, many will take short breaks between when several cases are to be fireformed. Some check this by carefully touching the barrel, and will take a pause if the barrel is to too hot to be held. After the fireforming is finished it is normal to thoroughly clean the chamber to remove any traces of lubricant, as lubricant in the chamber can increase the force on the bolt when firing live ammunition. The fireformed brass is then cleaned, especially around the neck (inside and outside) to remove lubricant and powder residue. The cases are then run through a 6 mm neck expander, which will be slightly oversized. Then the length is often trimmed to 1.486 inches (37.7 mm), although this step is not always necessary. Necks are then chamfered inside and outside. Afterwards the neck is turned to a thickness that will allow, at bare minimum, 0.001 inches (0.025 mm) 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 inches (0.0025 mm) - when one does the calculations, it is truly impressive how the dimensions of the neck turner can change over a 10 degree Celsius (21 degree Fahrenheit) range. The turner mandrel usually has to be lubricated between each case with a high quality 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.) The case is once again lubricated, and then run through a 6PPC full length sizing die with the expander ball in place. Primer is decapped, primer pocket cleaned and case lube removed, resulting in a case ready for ordinary loading.

As with other cartridges used in competition, precise handloading, a good rifle, and much 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 (6.80 to 7.45 g) 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. 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 grains (6.48–7.00 g) 6.5mm bullets, and the 6.5 BPC developed by Jim Borden and Dr. Louis Palmisano and optimized for 81–88 grains (5.25–5.70 g) 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 grains (7.13–7.65 g) 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 as a wildcat without SAAMI specs as the Grendel has, but which takes nearly all of the same factory-loaded ammo that the Grendel can take. The LBC has a more shallow bolt-face than the standard-spec Grendel which removes 0.01 inches (0.25 mm) of steel from (weakens) the LBC's extractor claw, but makes the LBC bolt compatible with 7.62x39 AR15/M4 bolts and barrels. The LBC's bolt and barrel are both incompatible with the SAAMI-spec Grendel's bolt and barrel, and retailers are often passing the 264 LBC as a "Type 1 Grendel" and calling the original, trademarked Grendel a "type 2 Grendel," which is the SAAMI spec but with more powder capacity, longer cartridge overall length, bolt compatible with the SAAMI-spec, and usually no compound-angled throat but a 0.300 inches (7.6 mm) throat. The .264 LBC-AR chamber is designed with a 0.295 inches (7.5 mm) neck like the 6.5 CSS, but not a compound-angled throat like the SAAMI-spec Grendel, and uses a 1 degree throat design like the 6.5 PPCX.

See also

Bibliography
  • Frank C. Barnes: Cartridges of the World. A Complete and Illustrated Reference for Over 1500 Cartridges. 10th ed. Krause Publications. Iola WI 2006. pp 21–22. ISBN 0-89689-297-2

References
  1. "6mm PPC data" (PDF). Accurate Powder. Archived from the original (PDF) on 2007-09-28. Retrieved 2007-08-21.
  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. 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. Archived from the original on 2006-05-12. Retrieved 2006-10-26.
  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.
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