In recent years, there has been a huge increase in the number of 6mm wildcats being shot out of AR-15’s. This movement was started and driven forward mainly by across-the-course high power shooters that have to compete at ranges out to 600 yards where wind drift can become a big problem. The existing commercially produced 6mm match bullet lineup has bullets that have a significantly higher ballistic coefficient (b.c.) than is typically available to those shooting with the .223 Rem. (or 5.56 NATO). For instance, the age old standard 600 yard loading for the .223 is the Sierra 80 gr. MatchKing bullet that has a b.c. of only .420, but the current 6mm Berger 108 gr. BT bullet has a b.c. of .546 and the 6mm Berger 105 gr. VLD bullet has a b.c. of .556. On a windy day at 600 yards the bigger 6mm bullets can be affected by the wind significantly less than the .223 Rem. counterparts.
This close up shows a 6mm Turbo 40 AR-15 rifle fitted for prone shooting with a sling and a scope. In this case, the top end features a heavy walled rigid billet upper receiver with a side charging handle. With a decent load work up these rifles are absolute "tack drivers" and can easily shoot 10 shot groups under .5 MOA.
A couple of years ago, we built up a magazine project rifle based on the 6.5 Grendel cartridge and the article was published as a Precision Shooting feature article. At that time, it was clear that the 6.5 Grendel cartridge had significant merit for competition shooting and varmint hunting out of an AR-15. Alexander Arms developed the 6.5 Grendel specifically for use out of an AR-15, and in a bold move, Bill Alexander (one of the principals in Alexander Arms), in bringing the cartridge to the U.S. market, contracted with Lapua to be the brass supplier for the cartridge. The net result was a supply of excellent quality Lapua brass suitable for shooting out of an AR-15. While the 6.5 Grendel is truly an excellent AR-15 cartridge in its own right, as I did the magazine project on the 6.5 Grendel, I kept looking at the cartridge thinking it was “just begging to be necked down to 6mm”.
The 6mm Turbo 40 (center) with its 40 degree shoulder, looks like the smaller Ackley type cartridge and here it is flanked by the 6mmAR (left) and the .223 Remington (right). Both the 6mmAR and the Turbo 40 have a case length that makes them ideal for using 6mm bullets out of an AR-15 platform.
Ultimately, I necked down the 6.5 Grendel case and made what is now called the 6mmAR cartridge (see also www.6mmAR.com). The 6mmAR has been very popular with not only high power shooters, but also varmint hunters and others. As usual, however, shooters are seemingly never satisfied with just stopping with what they have and there were immediate calls for even more power, performance and velocity. These requests ultimately lead to the making of the 6mmAR Turbo 40 Improved cartridge (some call it the “Turbo 40” for short).
What Is The Turbo 40?
Simply put, the Turbo 40 was designed to be a high performance 6mm cartridge for use in AR-15’s, although it certainly has application and uses in bolt guns. The cartridge is akin to a long bodied 6mm PPC but it also has a 40 degree Ackley type shoulder and body taper giving it approximately a 38 gr. water capacity vs. the 36 gr. water capacity typically associated with a 6mmAR and the 33 gr. water capacity typically associated with a 6PPC. It has the case capacity of a 6mmBR cartridge, and can easily shoot the big 105-108 gr. 6mm bullets up to the 2900 fps range. That’s a lot of performance out of an AR-15!
This 6mm Turbo 40 AR-15 Varmint upper was built up for varmint hunting in South Dakota - plenty of punch with rapid follow up shots and very low recoil! This upper is a "plug and play" setup and it pops right on any standard AR-15 lower.
The cartridge is made from Lapua 6.5 Grendel brass that is necked down in a Turbo 40 resize die and then fire formed in the rifle to blow out the brass and make a larger capacity case with a 40 degree shoulder angle.
If you want to get a mental picture of it, it looks like a slightly smaller 6mm Dasher and the cartridge uses a PPC bolt face. Hmmm . . . similarities to the Dasher & PPC cartridges? Yup, you guessed it, accuracy is great with the Turbo 40 cartridge as well.