The Lima Six belt fed upper receiver was announced in March, 2024 as a conceptual product. The idea was to make a belt fed upper for the AR-15 that was both more reliable and less expensive than other options on the market. Within two years the Lima Six advanced from CAD file, to prototype, to production unit. I’ve had the Wave 1 final product in my hands for months now, enough time to get more than two thousand rounds downrange… and it’s glorious.
Time to cover the OEM tech specs, then talk design . . .
Tech Specs:
- 5.56X45mm NATO
- 7075-T6 Upper Receiver and Top Cover, Type III Hardcoat Anodized
- 18” Chrome Lined Chrome Moly Vanadium Heavy Barrel
- Midlength Gas System (Direct Impingement)
- Midwest Industries 10” T-Series Combat Quad Rail
- Billet Machined Hardened 17-4PH Feed Tray
- K-Spec bolt with Dual Ejectors
- 8620 Bolt Carrier, Full Auto Cut
- Tool Steel Belt Feed Components
- Billet Machined Aluminum Charging Handle
- Threaded ½-28 with A2 Flash Hider
- Uses M27 5.56 links
- Uses M249 style “nutsacks”/drums
- Riflespeed Adjustable Gas Block
- Upper Weight: 7lbs 6oz
The technical data might sound similar to any other AR upper, but it’s far from it.
First, the Lima Six is indeed compatible with mil-spec AR-15 lower receivers…just not with the mil-spec bolt release. The buffer tube itself should be A5 length, especially if you’re planning on using a forced reset trigger. You can optionally run an AR10 short buffer (2.5″, H2) with a carbine buffer tube, but that rules out using an FRT. This information is subject to change as there are a few aftermarket manufacturers working on this as we speak.
The magazine well in the lower requires an adaptor to hold onto the M249-style drum, if using a traditional lower is indeed your plan. If you’re willing to get a little wilder, there are aftermarket lower receivers that forego the magazine well for a M249-style drum slot.
The Lima Six upper has an extra 3/4-inch of bolt carrier travel which, according to Lima Six, “assists in delinking rounds from the links. It also results in lower perceived recoil, and a more controllable rate of fire.”
Spoiler alert, there’s absolutely reduced recoil and a very controllable rate of fire in the Lima Six.
The top cover of the Lima Six is clearly M249-derived, with some notable deviations. For one, the top cover release button is on the rear. The top cover also has a “tensionable front pivot, two-point latch engagement, and an adjustable set-screw to take up any slack that may be present. These features result in an extremely reliable ability to hold zero even after repeated opening and closing. Initial testing shows that sub 2-MOA accuracy is achievable.” Another spoiler for you… accuracy testing showed 1.9-2.9 MOA groups with M193 ammo.
The Lima Six uses a reciprocating charging handle that’s bolted to the bolt carrier. Keep in mind the M249/M240 rule of thumb: charge the handle with your palm facing up, so if there’s a cookoff, you don’t snap your thumb.
The Riflespeed adjustable gas block is a perfect fit on the Lima Six. Adjusting gas takes mere seconds and is pretty important on the Lima Six given that I swapped from hot-loaded ammo to pretty mild loads and shot them both with a suppressor and without.
The Future is Aftermarket
Given that the Lima Six is a relatively new option on the market and doesn’t necessarily play well with all existing accessories, I want to highlight a few items that are presently, or nearly, available.
- Red Right Hand has some Lima Six-to-RPD conversions, heat mitigation systems, and alternative handguards
- Inoculum Group is working on a dedicated Lima Six lower receiver, and already offers a magazine-to-drum adapter.
- Hydra Weaponry has an AR15 lower receiver with quick change magazine wells, which includes a Lima Six M249 drum slot version.
- KAK has a Maxim style water-cooled Lima Six variation, multiple barrel options, and some gas blocks.
- Spite Werx is working on a whole M249 style furniture package for the Lima Six. I’m currently in the process of testing prototype parts. The final production list looks to contain a stock, handguard, grip, bipod, heatshield, and iron sights. Full disclosure, I’ve been talking with the owner of Spite Werx since he started and have helped with some design input. I have no financial stake or gain in his success.
- Hutson Arms is developing a long stroke piston kit for the Lima Six.
Break-In
According to Lima Six actual, this upper should be broken in over the course of 200 rounds with the gas wide open and no FRT or Super Safety installed. Past that period, swapping into an H3 buffer is the recommendation.
My first thousand rounds were all using Prvi Partisan PPU Rangemaster 55gr (M193 clone) ammunition which more than covered the break in period. I only ran into 3 failures to extract during break in, due to the gas setting being maxed out. Turning it down a bit solved that. A couple minor rough spots on the bold were smoothed out quickly.
At the Range
That first thousand rounds of 55gr PPU ammo went fast. Thankfully my kids were happy to help link up ammo for me. I needed an ammo drop and Ammunition Depot was kind enough to zip some PMC Bronze 55gr out to me so I could keep shooting. I also tried some Frontier 68gr match rounds while shooting groups.
The operating system of the Lima Six is smooth as silk. Recoil is laughably low, both in the perceived sense and in functional movement of the gun. The mechanical noise of the gun operating is also lower than with any traditional AR-15 I’ve shot, which is such a weird thing to say about a belt-fed gun.
I shot a few groups at 50 and 100 yards, having put a 5-25X optic on the Lima Six. The mil-spec trigger definitely held the gun back a bit, but the Lima Six still turned in respectable groups of 1.9 to 2.9 MOA with m193 clone ammo. Ironically, the Frontier match ammo came in at the 2.5+ MOA range.
Forced Reset Triggers, Super Safeties
The first question most people ask me about my Lima Six is if it will run a FRT/SS. The answer from my experience, and anecdotal experiences of others gathered from the huge official L6 thread on ar15.com, is an emphatic yes.
I’ve tried an Arizona Regulator, a FRT that fits neatly in between the upper and lower receivers, and a Grey Market Research Super Safety. Both have run very well with the Lima Six, but both quickly caused an issue where the upper wouldn’t fire any more due to insufficient ammo funds in my checking account.
I don’t care if you think that an FRT/SS isn’t a necessity. If you buy a Lima Six, I urge you to pick one up anyway. There will come a day when you’ll thank me.
Bottom Line
The Lima Six isn’t a cheap budget upper, nor does it behave like one. It transforms your AR into a belt-fed beast capable of quickly chewing through 200-round drums. This is also the least expensive way to get yourself into a belt-fed AR-15, and the most reliable as well in my experience.
A complete upper runs $2,999, and mine also came with an H3 buffer and orange Sprinco buffer spring. While it does take a chunk of change to buy one, I’m calling it a worthwhile, unique purchase that performs as beautifully as it looks.