Heavy Hitter – A Faxon-Foxtrot Mike 10mm Pistol Caliber Carbine Build

I’ve been a 10mm for years. It was only in the past few years that I actually got into it though. I have a couple of pistols I’d been messing with, but I really thought the 10mm cartridge would shine in a carbine or large format pistol.

I decided to finally take the plunge and put together a 10mm AR using parts from Faxon Firearms and Foxtrot Mike products.

Faxon Upper

10mm parts aren’t nearly as common as 9mm when it comes to AR components. Luckily Faxon Firearms supports the cartridge. I’ve used Faxon barrels on a number of my builds, and have always had very good luck with them. So I was more than happy to use one of their barrels and bolt carrier groups as the core of my build.

I went with a 10.5-inch barrel. I matched it up with a Faxon upper receiver, and Faxon M-LOK handguard. I wanted to keep things compact so I used a KAK Industry Micro Fluted Slimline flash can that just barely protrudes past the handguard. I finished the upper with a KAK Big Latch Charging handle. They’re basically a mil-spec charging handle with a large release latch. They’re affordable and work well. I have them on a bunch of my builds.

Assembling the upper was fast and easy. Being mostly Faxon parts everything fit together with no issues. I didn’t have to worry about a gas block or gas tube alignment either since the 10mm is a blowback design. The Faxon parts on the upper totaled $595.00. The KAK flash can and charging handle added another $48 bucks to the build.

The FM MIKE-45 Lower

When I started looking for lowers that took large frame GLOCK mags I found out that there aren’t actually a lot of options available. I wanted a last round bolt hold open too, and that posed a further problem. A number of the lowers I found with LRBHO required the use of a proprietary upper, and I had already had my Faxon upper complete at this point. After some looking though, I came across the Foxtrot Mike (FM) Products MIKE-45 lowers.

My buddy has a Foxtrot Mike 9mm carbine that we’d shot a number of times this summer. It’s a nice build and, ran and shot great. Having that positive experience in mind, I reached out to FM Products to ask if they thought my Faxon upper would be compatible with their lower’s LRBHO. They were great about getting back to me, and the answer basically was that as long as it was a typical GI spec upper, it should work fine. But there was a catch.

Foxtrot Mike had built their lowers for use with .45 ACP uppers. They are built to use GLOCK 21 mags, which means that they’d take 10mm GLOCK 20 mags as well, but they hadn’t actually tested them with 10mm. They were willing to let me give it a try though, and just asked for any feedback I had from running the 10mm on their lower. With that in mind, I had a MIKE-45 lower half on the way for my build.

Lower Details

Foxtrot Mike’s lowers are made from aircraft grade aluminum, and are finished with a matte black Type III anodizing. They come with an ambidextrous safety and a mil spec trigger assembly with a straight blade. The mag well is extra wide for faster reloads. The mag release itself is a big, easy to use billet paddle. A steel ejector, and last round bolt hold open are installed on the lower as well. Although FM sells these as .45 ACP lowers the lower itself is actually marked for Multi caliber.

The MIKE-45 lowers come with an A5 buffer tube and they use an AR10 .308 recoil spring along with a heavy 13.5 ounce buffer. The heavy spring and buffer ensure proper function with the .45 ACP or 10mm loads. The lower came fitted with a Thril Rugged Tactical AR Grip. I had never used a Thril grip, but it was solid and comfortable. I got a lower without a stock or brace since I planned on doing  a pistol build. I added a Magpul BSL arm brace to finish it off. The MIKE-45 complete lower half has an MSRP of $259.00 and is covered by a lifetime warranty. I thought that was pretty reasonable. The Magpul brace was another $60.

The Final Build

Since the MIKE-45 was a complete lower half, all I had to do was slap my upper on once the lower arrived. I added a Swampfox Liberator II optic that I had for testing to the upper and called the build good. The Liberator II is a multi reticle red dot with a 10,000 hour battery life and “Shake N’ Wake” feature. It uses a T-2 footprint and came with both a high and low mount for Picatinny rail. I have two previous generation Liberator sights that I’ve been using for years. The Gen II version has much better battery life as well as the Shake N Wake, along with a crisper reticle. Still, I’ve had great luck with my older Liberators so I expected good things from the Gen II. MSRP on the Liberator II is only $189.00.

The final build turned out pretty sleek. The Faxon handguards are slim, and the FM lower with its dedicated pistol mag well was fairly compact as well. Overall length of the build with the brace collapsed is 26.5 inches, and 29 inches with the brace fully extended. Weight with optic, and no mag is 6.4 pounds.

Range Testing

On my first trip out I mainly wanted to function test the build. I’d read that 10mm builds could be finicky. Plus, I wanted to see how the 10mm did with the MIKE-45 lower. I gathered up a bunch of 10mm ammo from my ammo locker and headed to my local range. I had predominantly 2A Warehouse 180gr FP’s, as well as some Steinel 180 FNFP and some Magtech 180gr FMJ loads.

I tossed out some Caldwell self healing reactive targets out at 25 or so yards and started loading magazines. FM only advises to use GLOCK factory mags in their builds. GLOCK factory mags are generally more consistent, and they can tune their builds to work with those. Aftermarket mags can vary in quality, so I can see why they advise using factory mags. With that said, I had a mix of GLOCK 20 15 round mags, SGM Tactical 30 round mags, and some ETS 20 round magazines.

I was pleased to see that my FM-Faxon build ran without issue. I put a little over 150 rounds through the gun in this break in session. I didn’t have any malfunctions with any of the mags or ammo combos. I did note that I would get last round bolt hold open with the SGM and ETS mags, but not with the GLOCK factory mags. There was no obvious difference I could see with the way the followers sat that I could tell, but the aftermarket mags locked back and the factory ones did not. Curiously, if I manually cycled the action with an empty factory mag in place, it would activate the LRBHO.

I didn’t bother with fine sight on on this trip, I was mostly concerned with function. With that said, the Swampfox Liberator II was pretty much dead on out of the box. At least good enough to steadily roll around my 5 inch reactive targets anyway. The circle dot reticle was easy to pick up, even in the bright sunlight. It’s a good fit for this build. It’s fairly lightweight, has great battery life, and seems to be recoil tolerant.

Speaking of recoil, I will say that a 10mm blow back has a noticeable increase in recoil over a 9mm. I’m not really recoil sensitive, but I definitely noticed it. Using the brace and getting the third point of contact for a cheek weld helped, but this may well end up being a good candidate for a Form 1 and an SBR stamp so I can put a real stock on it at some point.

The Boring Bench Test

I’ll be honest, I hate shooting from the bench for groups.  If you’ve read any of my other columns, you already know I much prefer shooting steel or reactive targets. Plus, in a defense shooting situation I’m not going to be shooting from a bench, so I don’t spend a lot of time doing it. With that said, I wanted to see what the Faxon barrel would do so I dug out my Caldwell rest and sandbags, and a variety of 10mm loads.

Being that this is still a pistol build I did my shooting at 25 yards. I dropped a 3x magnifier behind my Swampfox so that my old eyes could see the bullseye better. Despite usually finding bench rest shooting to be drudgery, I was actually glad I did it in this case. I knew the build shot pretty consistently from my prior plinking session, but I was really impressed with what I saw on paper. The 10mm Faxon build shoots like a laser. I tuned my sight slightly once I was on paper, and then rounds just started dropping into the red bullseye and didn’t stop.

I used a mix of loads from SIG SAUER, Freedom Munitions, Steinel, and Magtech. All of them produced groups well under 1 inch, with most being ragged one hole groups. In some cases I had 4 rounds considerably tighter, then threw one just a touch outside the main group. The MIKE-45 trigger is mil-spec. It’s decent, but not a match trigger. I was still able to get good consistent pulls and it had a positive reset, which helped with my consistency.

Freedom Arms 200gr XDEF HP          7/8″

Freedom Arms 180gr RNFP                 5/8″ (4 rounds were with 3/8″)

Magtech 180gr FMJ                                7/8″

SIG SAUER Elite 180gr JHP                 13/16″ (4 rounds were within 1/2″)

SIG SAUER 180gr FMJ                          5/8″

Steinel Ammo 180gr FMJ                      7/8″

After the bench testing I went back to what I knew best, blasting plastic jugs. The 10mm, especially with the hollowpoint loads, quickly shredded the jugs and I was left with sniping broken bits of clay bird off the back stop after that. Which I had no problems doing at all with the Liberator II sight, even without the magnifier, and the Faxon-FM build.

Reliability in this session was again 100%. I actually got a couple of LRBHO’s with the GLOCK factory mags this time, although I couldn’t say why. It didn’t do it every time, and it wasn’t always with the same magazine. Hold open was still consistent with the SGM Tactical mags. I didn’t bring the ETS mags with me on this range trip.

When it came time to clean up brass, my buddy and I noted that ejection was extremely positive. As in it was kicking the brass a good 20 feet away at about the 4:00 o’clock position from the ejection port. Luckily the Faxon upper has the Brunton bump case deflector, so it kept my left handed shooting buddy from getting blasted in the face with the brass.

10MM is the Best MM

I have to say, I wish I would have built a 10mm like this years ago. It’s a thumper. It hits hard, but was also surprisingly accurate. I really need to take it out to at least 50 and 100 yards to see what it does, and I will do that on a future range trip. I wish my club had steel at those ranges, but I guess I can grudgingly shoot at paper again, just to see what it does.

The combination of Foxtrot Mike lower and Faxon upper proved to be a winning combination. It’s an ultra reliable build which I’m sure is the result of good design and quality parts from both Foxtrot Mike and Faxon.

I want to solve the issue of the factory 10mm mags not locking back. The Foxtrot Mike rep said that I may be able to tweak the LRBHO, but I’ve been hesitant to play with that just yet because I also built a .45 ACP upper to use with the lower, and that works perfectly with GLOCK 21 and KCI mags. In the meantime, I know the holds open works with my SGM and ETS mags, so just need to be aware that it may not always do so with the GLOCK mags. It’s not a deal breaker for me, especially since not all PCC’s have LRBHO to begin with. Plus, considering how well the platform is working otherwise, I can forgive it not liking one brand of magazine.

Aside from being a fun gun to shoot, the 10mm PCC build should be a great home defense gun or even  a hog hunting gun. It would certainly give me an excuse to finally go hog hunting, which I’ve been saying I want to do for years now. It took me long enough to finally build a 10mm PCC, so now I need to put it to work.