CSA45: The Mild Mannered Carbine

CSA45: The Mild Mannered Carbine


The CSA45 carbine by Flint River Armory is a gas piston design chambered in 45ACP. In the world densely populated by AR15 derivatives, it’s an original development with several novel features, manufactured in Huntsville, Alabama. The receiver is machined of billet aluminum and uses AR15 pistol grip and fire control parts, but the four-lug rotating bolt is proprietary. Its collapsible stock rides on a robust tube that is integral to the lower. The adjustable short-stroke gas piston allows the carbine to be tuned to specific loads for minimal felt recoil. The left side reciprocating charging handle is easy to rack against a relatively light recoil spring.

The CSA45 uses a proprietary drop-free steel magazine, surprisingly lightweight, holding 25 rounds in a double-stack, single feed configuration. Unlike most such magazines, it is easy to load. The tapered top makes it easy to insert into the mag well. The bolt stays back on the last shot. The magazine weighs 0.4 pounds, compared to the 3/4-pound weight of the dimensionally similar M3 Grease Gun mag.

Three screws holding the gas system in are visible.

The muzzle comes threaded for accessories, such as sound suppressors. The enclosed receiver back, along with gas piston operation eliminates any blowback in suppressed use. While the gas system permits a lightweight bolt carrier, the overall weight of the carbine is 6.7 pounds with an empty magazine, about the same as that of the old Olympic Arms blowback 45ACP AR15. The difference is the much milder recoil impulse and the full-length free-float KeyMod rail on the CSA45. The carbine has excellent balance and shoots as well off hand as off a bench. Competitive shooter Amiee Williams, a fierce but diminutive woman, found it very quick and handy for ringing steel plates at speed. A lighter braced pistol and an SBR variant with 10-inch barrel are also available.

Takedown is similar to that of an AR15, with two captive pins holding the upper and the lower together. Once the lower is separated from the upper, the charging handle comes out to the side, and the bolt and carrier group slide out of the back of the upper. The gas system is retained with three 9/64-inch hex head screws; backing them out allows the entire piston and spring assembly to slide out of front along with the forend. The bolt and the gas piston may be further disassembled for detailed cleaning.

Although the instruction manual recommends sticking to brass-cased ammunition, the CSA45 ran well with steel-cased Tula ball. While the 230-grain 45ACP cartridge gains only slightly from the 16-inch barrel, lighter loads pick up 30-40% extra muzzle energy. A 185-grain +P load exceeds 1,400 feet per second from the 16-inch barrel, in contrast to 1,200 feet per second from an M1911, while standard pressure 185-grain loads go from 1,000 feet per second to 1,200 feet per second, respectively. Between the low recoil and flatter trajectory, this carbine is much easier to keep on distant targets than a pistol. While both pre-production and early production samples shot 10MOA with all loads, the practical accuracy is out of proportion to the theoretical limitations. Wide shot dispersion seems to be the bane of gas-operated 45ACP carbines, with the direct impingement BAZ45 yielding 12MOA at best. Charley Groves, the president of Flint River Armory, says that current production carbines shoot 3-4MOA. Several other shooters reported “golfball 25-shot groups at 25 yards.” Unlike BAZ45, CSA45 isn’t picky about ammunition and can be tuned to work with the weakest puff loads or the stoutest +P rounds. Left in default configuration, it already runs everything I’ve been able to find.

Only one of the two push pins is on the lower.

Felt recoil depends on the buttstock placement. For reasons that FRA hasn’t explained, the stock is open in the area over the tube. Placing the solid portion of the stock over the shoulder results in a gentle push not much greater than from a .22 rifle. Shifting the stock lower, with its top edge even with the top of the shoulder, puts the ridged hollow part against the shoulder and hurts considerably with every shot. The problem is simple to remedy with a slip-on rubber recoil pad, but none of the commercial pads I had on hand were wide enough to fit over the buttstock. That ergonomic issue should be corrected. While something as simple as a glued-on mousepad could remedy it, I’d like to see a factory solution. The rest of the carbine is nicely chamfered, with no sharp or abrasive spots. Unlike on an AR15, the bolt hold-open latch cannot be used to drop the bolt; pulling on and releasing the bolt handle accomplishes that.

My pre-production sample is owned by the FRA president and has shot very reliably despite the many thousands of rounds put through it in demonstrations and testing. I’ve had no parts breakage and very few malfunctions. Early feedback from high volume users indicates that the ejector design is not durable. FRA came up with a definitive fix for that, requiring trilling of the receiver to install the stronger ejector. All current production carbines already have that improved part installed from the start. A 9×19 Luger variant is expected in the near future, with 10mm and other calibers possible after that.

The CSA45 has several things going for it. Disassembly and maintenance are very simple, and the gun runs very cleanly. The carbine runs cool, allowing well over 100 consecutive shots before the forend warms up. Recoil is mild, and—once the buttstock is covered—feels that way. There’s nearly no muzzle rise on recoil, allowing rapid follow-up shots. Given the limited mechanical accuracy, it’s definitely best for ranges under 100 yards, but its fast handling makes it very formidable up close. Especially in the shorter rifle or braced pistol form, it has much to recommend it as a defensive weapon.

The piston key is integral to the carrier and very robust.
Partially hollow buttstock needs a cover for comfort.
Double-stack, single-feed magazine works with all bullet shapes.