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The .408 Chey Tac (10.4×77mm) as it is commonly known, or by its full name, .408 Cheyenne Tactical, is a counter-sniper rifle cartridge, developed by Dr. John D. Taylor and machinist William O. Wordman. This cartridge was designed specifically for the market to the military in hopes it would be both a cost-effective and ballistically superior round to the existing military long-range cartridges; the .338 Lapua Magnum and .50 BMG.
To date, the .408 Chey Tac has seen service with the Jordanian SRR-61 Regiment, the Polish GROM operatives, the Turkish Maroon Berets operatives, and the United States Marine Corps. It also has a growing following among civilians that enjoy long-range and tactical shooting.
The .408 Chey Tac was originally developed and produced by two companies, first THEIS (Tactical High Energy Impact Solutions), now defunct, which provided the modification necessary to translate what modifications became apparent and necessary from the original .505 Gibbs case. The second entity involved in the cartridge development was Lost River Ballistics Technology which is now closed and much of the intellectual property was absorbed by Greenwich Ballistics (a CheyTac LLC based company). Jamison International has been, up until recently, the primary producer of the 419-grain projectile that is the patented 'CheyTac' cartridge. Despite this, many companies offer similar .408 cartridges that work outside the patent and provide excellent results such as the now commonplace 400-grain solid projectile.
The tactical takedown .408 rifle was originally designed by Bill Ritchie of EDM Arms. Ritchie was approached by CheyTac LLC to scale down his Windrunner rifle to accommodate and better suit the .408 Chey Tac cartridge. CheyTac LLC began looking at options to modify the rifle and add the popular over-the-barrel bipod system and shroud after the initial field testing of the EDM Arms rifle was completed. Initial field testing was provided by a company, now defunct, known as Sniper Operations Executive.
CheyTac LLC and EDM Arms had a multi-million dollar lawsuit filed in the early 2000s which resulted in the case being dropped and the decision was for both companies to continue producing their respective rifles in the .408 chambering. EDM Arms later partnered with THOR Global Defense Group to provide official license of the original rifle (now the THOR XM408) and the enhanced model which featured an enhanced bipod and carry handle system (the THOR M408). CheyTac LLC continued to produce their rifle through a reverse engineering process and had several machine shops over the course of the next few years to produce the rifle under an ATF variance.
CheyTac LLC later approached RND Edge in regards to having a semi-automatic .408 rifle created for standard production. Initial prototyping was completed, but after some developments, RND Edge has separated from CheyTac LLC, and a semi-automatic CheyTac rifle was not officially brought into production.
It became apparent that with the extreme range that could be achieved with the .408 cartridge, a ballistic computing system would be quite a boon to providing a quick calculation of the Data On Personal Equipment, enabling the shooter to efficiently apply shots on a target at extreme ranges. The software was deemed 'ABC' and was produced to work on Windows mobile platforms. The traditional ABC software is no longer available in original form, but several companies now offer similar systems to provide calculation on both Windows operating systems as well as newer Android applications.
The .408 Chey Tac is based on a wildcat cartridge, the .400 Taylor Magnum. The .400 Taylor Magnum's parent case is the .505 Gibbs. Although the exterior dimensions would lead the casual reader to believe that the .408 Chey Tac is a necked down version of the .505 Gibbs to .0408 inch (10.36 mm) diameter, this would be a mistake.
The .505 Gibbs is an old English big game cartridge that was designed to handle 39,160 psi (270 MPa) of internal pressure. This case in no way can safely handle the 63,800 psi (440 MPa) of internal pressure created in today's modern magnum rifle cartridges. The new .408 Chey Tac's internal dimensions were changed to accommodate thicker walls at the case web for a higher working pressure. To interchange, the .505 Gibbs case and .408 Chey Tac case will lead the shooter and firearm to damage, destruction or a fatality. The .408 Chey Tac is a new design and thus has no parent case.
- .375 Chey Tac. This round is basically the .408 Chey Tac necked-down to the smaller caliber. The .375 Chey Tac has slightly higher ballistic coefficient than the .408 Chey Tac.