The .366 TKM is a Russian straight wall "shotgun" cartridge, based on the 7.62x39 and was designed by Russian company Tekhrim possibly around the early 2010's. It fires .377 caliber (9.58mm) bullets according to The Firearm Blog.
The cartridge was created as a workaround to Russia's strict regulations on rifles, but much lighter regulations on shotguns. As a result, these .366 TKM "shotguns" are smooth bore (either Paradox bore or Lancaster bore), and act largely as a slug gun would, primarily firing solid projectiles rather than shot, although shot shells also appear to be available.
It should also be noted that since it is based on the extremely popular 7.62x39 cartridge, many firearms are readily convertible to the .366 TKM cartridge if one were so inclined. This is also true of 7.62x39 magazines, which are also compatible with the TKM cartridge. However, it's unlikely that other 7.62x39 accessories such as muzzle devices will be compatible due to much larger bullet diameter found in this cartridge.
The Firearm Blog has most the following ballistic data on the .366 TKM. This site contained the brief data on the "EKO" (eco) loading below, which contains a solid zinc projectile:
|Bullet Weight (gr. / grams) & Type||Velocity (feet per second / meters per second)||Energy (foot pounds / Joules)|
|170 gr. (11 g) FMJ Slug||2,295 fps (700 m/s)||1,988 ft lbs (2,695 J)|
|208 gr. (13.5 g) Polymer-Coated Lead||2,100 fps (640 m/s)||2,036 ft lbs (2,760 J)|
|231 gr. (15 g) FMJ or JSP Slugs||2,030 fps (620 m/s)||2,113 ft lbs (2,865 J)|
|100 gr. (6.5 grams) Solid Zinc||2,657 fps (810 m/s)||1,568 ft lbs (2,126 J)|
A 20 gram (308 gr., .7 oz) birdshot load is mentioned in the TFB article as well, but velocity is unclear. Although, with that heavy of a load for this cartridge, it's likely to be on the slower side.
This website also shows off a very interesting self-contained polymer shotshell type loading for the .366 TKM. It is claimed to be 6.2 grams (~ 96 grains, or nearly a quarter-ounce of shot), which seems more practical and believable than the previously mentioned load, but velocity was hard to track down for this particular offering as well. Perhaps this is a higher-velocity lighter load for the cartridge, where the 308 gr. loading mentioned previously really pushes the weight limits of the round, but has to slow things down.
The .366 TKM has a larger counterpart, also designed by Tekhrim and Molot (?), based on the 7.62x54r cartridge - the 9.6x53mm Lancaster. Further, there are several more counterparts in the cartridge family, including the .366 Magnum (based on 8mm Mauser and also firing the TKM's .377 caliber projectiles), as well as the .345 TK, based on the 5.45x39 cartridge, shortened to just 23mm and containing .345 caliber (8.76 mm) bullets.
The TKM cartridge also appears to be overall quite similar to the Russian military's 9x39 cartridge, which fires similar-caliber projectiles, and has a similar cartridge length, though there are certainly differences in cartridge dimensions, especially in that the .366 TKM is straight-wall and has no shoulder. This may be due strictly to regulation so as to be considered a shotgun cartridge or other factors. It also may be possible that Tekhrim & Molot wanted to avoid creating a cartridge too similar to the Russian military cartridge for regulatory reasons, but these reasons are conjecture.
A Rifle Without Rifling?
This article at ModernFirearms.net does appear to provide valuable insight on the matter. It suggests that the .366 TKM cartridge was designed to be used in firearms with Paradox bore or Lancaster type bores, both of which provide a sort of all-in-one alternative to other types of bores, both rifled and smooth. For example, a "paradox" (aka "ball and shot") type bore, is almost entirely smooth bore, with several inches of rifling at the muzzle end. This still allows sufficient use of both solid slugs, as well as shot. This provides the same effect of using, for example, a rifled choke tube for slugs). On the other hand, a "Lancaster" type bore actually uses an oval-shaped bore in order to engage projectiles and provide spin, while also still allowing for sufficient use of shot.
In Pop Culture
Escape From Tarkov
The 366 TKM and firearms chambered in this cartridge, are featured heavily in the popular first person shooter video game "Escape From Tarkov", developed by Battlestate Games of London, England. Firearms chambered in the cartridge, as well as various in-game ammo types correspond heavily to real-world offerings. For example, the Molot VPO-209 semi-automatic rifle, as well as the Molot VPO-215 bolt-action rifle are both available in-game. Likewise, various ammunition and bullet types such as standard FMJ, "EKO" solid zinc bullets, and more.
- ModernFirearms.net - A page from ModernFirearms.net featuring some information and basic (estimated?) ballistics on the .366 TKM.
- The Firearm Blog (TFB) - An article from The Firearm Blog aka "TFB" from 2015 when the .366 TKM was really beginning to hit the Russian market. It gives an overall introduction to the cartridge, as well as some ballistic data.
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