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. At distances out to 300 meters, it is one of the most accurate cartridges available. This cartridge's accuracy is produced by a combination of its stout posture, being only long, and aggressive shoulder angle of 30 degrees compared to a 30-06's 17 degrees. Today it is commonly used for railgun shooting matches and has been since the 1980s.
Background.
The cartridge is a necked-up version of the .22 PPC which is in turn based on a .220 Russian (5.6×39mm). The standard bullet diameter for 6 mm caliber cartridges is , 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, 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 accurately. The cartridge developed enough acceptance that rifles chambered for it are available commercially.
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 , 6PPCs with , , or 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.
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 at .
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 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. Others are the 6.5 CSS marketed by CompetitionShooting.com, the 6.5 PPCX developed by Arne Brennan and optimized for 6.5mm bullets, and the 6.5 BPC developed by Jim Borden and Dr. Louis Palmisano and optimized for 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 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.
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 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 throat. The .264 LBC-AR chamber is designed with a 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.