Once, not long ago, the U.S. Army chose the 5.56×45 NATO cartridge as the standard round for their M16 rifles. The 5.56 performed reasonably well and had decent terminal velocity. Then, for a multitude of reasons, the U.S. military changed the make of the standard M16 rifle and went to the M4 version with a shorter barrel. The 5.56 NATO cartridge didn’t fare as well with the shorter barrel.
Remington, with the help of the U.S. Army Special Forces Command and Marksmanship Unit, developed the 6.8 SPC (Special Purpose Cartridge) to address some of the deficiencies of the 5.56 NATO round.
The 6.8 SPC began appearing in semi-automatic civilian rifles in 2006, and by 2007, several manufacturers were offering AR-15 uppers for this cartridge. The military, in the meantime, has decided against adopting the 6.8 SPC. 6.8 SPC uppers continue to grow in popularity with civilian shooters who are looking for a bit more out of their AR-15 platforms than the traditional 5.56 NATO round.
There are many companies making parts for 6.8 SPC Upper assemblies. Only a handful are selling fully assembled and ready to shoot 6.8 SPC uppers. The upper assemblies that I have chosen for my list of the best 6.8 SPC upper receivers provide the necessary quality, precision, ad reliability required in combat-style firearms. The 6.8 SPC are not radical firearms, but there are some things that anyone considering adopting this caliber should understand.
When you start shopping for a 6.8 SPC upper, the first thing you may notice is the designation etched into the barrel. Most new 6.8 SPC barrels carry the designation 6.8 SPC II. The difference between the two barrel designations is minute, but very important.
The original specifications for the 6.8 SPC rifle barrel chambers according to SAMMI have a chamber with .05 inches of freebore. These are perfectly functional barrels, but some shooters experienced pressure spikes when loading cartridges near the maximum end of the load tables. Many manufacturers began building SPC II spec barrels with a freebore of .114 inches, which reduced these overpressure symptoms considerably. Most reloaders report that this change also helped the ballistic characteristics and accuracy of the 6.8 SPC.
You should note that most companies producing 6.8 SPC Upper Receiver packages opt to use the SPC II chamber. Some barrel manufacturers still make barrels with the old chambering, but they are getting increasingly hard to find.
The 6.8 SPC cartridge was designed from the beginning to work with standard AR-15 lower receivers and magazines. The 6.8 SPC round fits a standard AR-15 magazine, although some magazines may hold one or two rounds less than if loaded with 5.56 NATO.
Converting an AR-15 from a 5.56 NATO upper to a 6.8 SPC upper requires nothing but pulling the mounting pins and making the change. Everything else should work correctly. You will notice that the gun now has slightly more recoil. Some users have reported that changing the buffer and buffer spring to a heavier configuration takes some of the recoil away and seems to help the action operate better.
If you are interested in purchasing a 6.8 SPC II Upper for your AR-15 lower, these are our recommended choices for the conversion. The 6.8 SPC II upper receiver packages are, in my opinion, the best combination of quality, reliability, and accuracy available on the market today.
Palmetto State Armory gets our nod for the best 6.8 SPC upper kit when comparing features versus price. Palmetto State Armory has built an industry reputation for producing parts, kits, and complete rifles that offer some of the best features without a gut-wrenching price. The Palmetto State Armory 18″ mid-length upper receiver meets these expectations.
I am a big fan of Palmetto State Armory products and have several AR-15 platform rifles in my safe that owe their existence to Palmetto parts. In my opinion, Palmetto State Armory offers dependability and superior customer service. As far as features, you will not find any shortcomings in the features list provided by Palmetto State Armory products.
- The barrel on the Palmetto State Armory 18″ upper receiver package is a 416R stainless steel chambered for 6.8 SPC II. The barrel is cut with a 1:11 twist and features an M4 extension and a mid-length gas system.
- Each Palmetto State Armory 18″ upper receiver package come with a PSA 15″ Lightweight M-Lok free float rail, .750″ adjustable low-profile gas block, and an A2 flash hider.
- Each Palmetto State Armory upper receiver is milled from forged 7075-T6 aluminum that is finished with a hard coat anodized finish. Each upper receiver is manufactured to MIL-SPEC specifications for compatibility and durability.
- The internal operating parts are of the same high quality. The BCG in each 6.8 SPC II upper receiver from Palmetto State Armory is crafted from 9310 steel ad nitride treated for long life and corrosion resistance.
- These 6.8 SPC II upper receiver assemblies are complete with a standard charging handle and ejection port cover. These uppers come ready to go to the range.
There may be more expensive 6.8 SPC uppers on the market, but I don’t think there are any that can offer the same features at such a competitive price. I think these are great guns and offer performance for a fair price. I find dealing with PSA a great experience. If you compare this upper receiver to others on the market, you won’t find a better deal for the money.
Blackstone Arms may not be a name that many shooters know. However, Blackstone has been producing fine AR platform firearms and assemblies for many years and enjoys a solid reputation among its customers. My choice for a 16″ 6.8 SPC II upper comes from Blackstone in the guise of their 16″ Scout model.
Blackstone features its unique rifling system. The 16″ Scout comes with the Blackstone 3R rifling. Blackstone asserts that this 3-land rifling pattern improves ballistic characteristics and reduces pressures to improve bullet performance. Blackstone doesn’t skimp on the other features of this upper receiver package and offers a variety of user-selectable parts to complete the upper build.
- Each Blackstone complete upper features an AR performance 16″ barrel with 3R rifling cut to a 1:11 twist. Each barrel is fitted with an M4-style muzzle device and a choice of hand guard options. The default handguard is a Troy industries 11″ hand guard.
- A mid-length gas system finished with a low-profile gas block and a melonite finish completes the barrel assembly.
- Blackstone builds their 6.8 SPC II complete uppers using Aero Precision uppers. These are extremely well-built upper receivers, and they compliment the precision of the barrel options from Blackstone.
- Upper receivers are squared and milled to ensure precision barrel alignment. This s a feature not offered by many manufacturers of complete uppers.
- The BCG included with these packages comes with a melonite finish and is precision machined to keep tolerances low and performance high. A standard MIL-SPEC charging handle is fitted to each upper receiver package.
The 6.8 SPC cartridge can be finicky. Finding the right length to get the best performance can be tricky. The Blackstone combination of a 16″ tube and their 3R rifling seems to offer shooters the best of a shorter configuration with a high level of performance from the standard 6.8 SPC loads. The price is a bit higher than some other manufacturers, but what you get more than offsets the extra expense.
Moriarti Armaments is far from being a household name, even among dedicated shooters. They are a relatively small manufacturer and seller of AR-15 products and accessories with a good reputation among their customers. Of interest here is the 10.5-inch complete upper receiver package from Moriarti Armaments.
There are some tradeoffs if you go to a short barrel. The first hurdle is the federal requirements to register a firearm with a 10.5-inch barrel as an SBR and purchase the tax stamp. This registration requirement puts a lot of people off this kind of firearm build. The other option is to build a pistol kit which negates the need for a tax stamp, but does impose some other regulatory burdens.
From an operational standpoint, the shorter barrel does reduce the ballistic characteristics of the 6.8 SPC cartridge. The result is less speed and reduced effective range. However, for self-defense or close-quarters combat rifle, this may not be an issue. In any event, the features provided by the Moriarti Armaments SCP II upper receiver won’t disappoint.
Moriarti Armaments also allows customers to customize their upper receiver with various after-market components of different brands to mark your gun as your own.
- Each Moriarti Armaments 6.8 SPC II package includes a 10.5-inch nitride-coated M4 style barrel.
- Each barrel supplied with a Moriarti Armaments 6.8 SPC II package includes a carbine length gas system with a .750-inch gas block and a 1:10 twist rate on the rifling.
- The package features a flat-top M4 style receiver with and carbine length M-Lok forend.
- An A2 flash hider, forward assist, and ejection port cover finish the package.
One thing you need to consider when purchasing a Moriarti Armament upper is the need to order the bolt separately. The bolt carrier groups is not included in the package price shown in the advertisements. Beyond that, these are complete uppers that make greater guns. The price is bit more than other brands, but in many ways, these guns are well worth the extra price.
If you are interested in taking full advantage of the range available with the 6.8 SPC cartridge, a longer barrel is recommended. Our pick for a complete upper assembly in 6.8 SPC for range and accuracy is the Bison Armory 22″ Heavy Barrel complete upper receiver.
Those few extra inches on the barrel will give you a bit more velocity and tighter groups on the range. Bison Armory may not be a manufacturer on your shipping radar, but they deserve a look if you are serious about your rifle and accuracy. Bison Armory offers a complete line of 6.8 SPC uppers from which to choose, and they all include these features.
- The Base grouping for each Bison Armory upper kit includes the upper receiver with ejection port door and forward assist, a bare stainless barrel, low profile gas block, gas tube, forearm and a Stag 6.8 bolt.
- You may choose a different bolt at the website store as you make your selections. All bolts and bolt carrier groups are thoroughly inspected and head spaced before leaving the factory.
- If you elect to purchase your bolt carrier group from Bison Armory, it will be inspected, assembled with the bolt, and fitted to the upper receiver before shipping. This installation includes the gas key and firing pin, retaining pins and cam pins.
- Bison Armory builds its barrels from 416R stainless steel. Each barrel has a 6.8 Bison chamber, 4-groove / 1:10” twist button rifling, a 5/8-24 thread muzzle, rifle length gas system and M4 feed ramps. The barrel and receiver are hand-fitted for perfect alignment and great accuracy.
- You can pick from a variety of forearms styles and manufacturers as you order your Bison Armory upper receiver. These complete upper assemblies make great guns when paired with your AR-15 lower receiver.
If you want accuracy, unparalleled quality, and stand-up customer service, Bison Armory is the place to go. The 22″ heavy barrel assembly for 6.8 SPC is my choice for building a rifle that gets the most out of the 6.8 cartridges. I don’t think you will be disappointed either.
If you want to start shooting 6.8 SPC out of the box, a complete upper receiver package is the way to go. You save time assembling the parts yourself. Simply open the box, attach the upper to your lower and you are range-ready. Whether you are interested in hunting or competitive shooting, one of these manufacturers can help you assemble a 6.8 SPC upper to meet your needs.