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Review: X-Caliber Mfg. Custom AR-15 Barrel

Review: X-Caliber Mfg. Custom AR-15 Barrel

While “custom” rifles are nothing new, there are few truly custom rifle shops, and that number drops drastically when looking for custom AR-barrel manufacturers. One of the best in the business is X-Caliber, which offers a host of services, including engraving, fluting, threading/crowning, chambering and contouring of its barrels.

I recently ordered one of the company’s 6X45 mm barrels (a cartridge based on the .223 Rem./5.56 NATO case necked up to accept .243/6 mm bullets). What I ended up with was a work of art, both in form and function. X-Caliber made the process simple. I knew I wanted a 6X45 mm, but finding one that matched my barrel wish list was impossible. Enter X-Caliber’s easy-to-use ordering system.

First, I only needed to select which barrel design I was after (X-Caliber offers AR-15, AR-10, Savage and Remington barrels, and unturned/contoured barrel blanks). The fun of perusing the company’s seemingly endless options began.

Starting with the steel type, for my AR-15, I chose the 416R stainless steel variant over the 4140 chrome-moly steel. While the chrome-moly tends to maintain accuracy through a higher shot count, I went with 416R, as it tends to be a tad more accurate. I then chose my desired barrel length. While X-Caliber offers barrels ranging from 7- to 28-inch long barrels, I opted for a 26-inch barrel. Part of the goal with this project was to suppress a heavier match bullet (I knew friction would help slow the bullets down), and I was more likely to reach my subsonic goal using Hodgdon’s Trail Boss powder. However, that length also wouldn’t prevent me from shooting lighter bullets at relatively normal speeds, either (I’ll get to my results in a bit).


After selecting the steel type and the barrel length, the options for caliber, twist rate and chamber were picked. Calibers ranging from .17 to .500 are available, with various rifling options to choose from (depending on caliber), as well. I went with a .243/6 mm caliber with a 1:7-inch twist rate using 5R rifling. I knew the lighter bullets weren’t so light that the heavy twist rate would overstabilize the bullets, yet the twist was tight enough to work with the heaviest projectiles.

As for the chamber, though X-Caliber offers .17 Fireball through .50 Beowulf, I wanted a cartridge for which plenty of cases were available, so a .223 Rem.-based case was my best option for reloading purposes. Considering I already had plenty of .243 bullets available, with several to choose from for whatever purpose I could ever want to achieve, the 6X45 was the obvious choice.

For those unaware of the ballistics of the 6X45 mm, the rule of thumb floating around on the internet is you can propel a 10-grain-heavier projectile at the same velocity as a .223/5.56 would with a 10-grain-lighter bullet. So, for example, a 65-grain bullet out of the 6X45 mm would go roughly the same velocity as a 55-grain bullet from a .223 Rem. There are also more match, varmint and hunting bullets and bullet weights available for the .243-inch bullet diameter, to boot, and it will buck wind better and hit harder while maintaining roughly the same trajectory as a .223 Rem. After selecting the rifle’s chambering, I then picked the gas-system length. With a 26-inch tube, a rifle-length gas system was a given.

I was also able to pick the contour. Here’s where X-Caliber was incredibly helpful. Rather than displaying a blueprint of the barrel, leaving readers to determine which measurement belongs to what part of the barrel, X-Caliber simply lists the profile diameters at each main measuring point. For AR-style rifles, for example, X-Caliber listed the barrel’s diameter at the receiver, the gas block and the muzzle.

Speaking of the muzzle, that’s one more way X-Caliber makes the process easy. The company has taken the standard muzzle-thread dimensions for a given caliber range, and simply matched the common thread patterns to a range of calibers. In other words, any barrel with a caliber of .243-.358, like mine, has the common 5/8-24 TPI thread pattern, so I just picked the threading that corresponded to the caliber range in which my selected caliber fell.

Then came the extras. Fluting, which is offered in nearly a dozen styles and includes fluting only in front of or behind the gas block, or both, was one thing I was interested in, considering my barrel used a bull-barrel contour. The company’s proprietary thermal fluting helps reduce heat, which in and of itself offers several benefits, so that’s what I selected at the rear of the barrel, and then I opted for standard straight flutes in front of the gas block for a clean look.


Some other choices included a polished or matte finish, a cryogenic treatment and a Cerakote coloring (this was something new that wasn’t offered at the time I ordered). I also opted to top the muzzle with one of the company's brakes, which are matched to the contour of the bull barrel.

Prices start at $280, which is incredible, considering as long as you stay within a few parameters (my 26-inch barrel, for instance, added to the price, as did a cryo-treatment and fluting), but even my oddball chambering didn’t add to the price, nor did the change in contour or the muzzle threading.

X-Caliber offers other muzzle brakes, as well, for those interested, and barrels come with a one-MOA-or-less guarantee, provided customers use certain bolts and send them in to get an exact headspacing job, too (which I didn’t do).

Upon test firing, I’m pleased to report the barrel shoots to within an inch of the same point-of-impact. I’ve handloaded multiple bullets for the platform, including a Nosler 80-grain Ballistic Tip Varmint bullet and an 80-grain Barnes TTSX bullet. What’s more, each load prints under an MOA, and that’s using the initial load I tried for each bullet (all other load components are identical including primers, brass, and powder type and charge).

Considering there was no fine-tuning of loads whatsoever, and those groups were shot before the barrel was even broken in (I used X-Caliber’s recommendations for breaking in the barrel), I have no doubt the barrel will shoot better after I fine-tune the load and the barrel break-in process is complete.

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