New Frontier 10mm AR15 Pistol Build

I have had a bit of a romance with the 10mm round… you know not the neutered 10mm rounds, the actually full bore powerhouse rounds. With the real deal 10mm rounds, you have a handgun which can deliver 650, 700, and even 780 ft/lbs of energy. That is approaching rifle round energy levels and definitely delivers large magnum rimmed handgun power all in a glorious high capacity semi-auto format. In the case of the Glock G20 that is 15+1 rounds on tap and the compact sized G29 with 10+1 round. That my friends is a hell of a lot of power for a handgun. Both of those guns I own and enjoy shooting. When I heard that New Frontier was offering a AR15 lower and upper set which could be used for a 10mm AR15 pistol build I had to go for it.

I am likely one of the first writers to have worked up such a build and I did it with the intent to have a sub-gun format AR15 pistol that could be tucked into any pack or messenger bag. Let me tell you this tiny setup is a thumber.

BUILD SPECS

Like many of the handgun round AR15 builds, this New Frontier based build does not use a gas direct impingement system, but a standard recoil based action. The result is a very heavy solid steel recoil taming New Frontier .40/10mm carrier that you could use as a mini-sledge and a super heavy Kaw Valley 10oz buffer with extra power buffer spring to strip off a round from the stubborn Glock mags and drive that beast of a carrier back into battery.

Kaw Valley Precision is having Faxon make both the .40 S&W and this 10mm chambered barrels so you know they are very high quality, but Kaw Valley has a great brand based on delivering of all the pain in the butt parts for a build like this. This barrel is a KVP 4.5-inch 10mm barrel tipped with a KVP brake. KVP offers the heavy buffers and springs, barrels, and a really nice blast/concussion forwarding brake specifically designed for the .40 S&W and 10mm sized rounds. I even used their very slim carbon fiber handguard which is perfectly sized for the barrel length and brake. Kaw Valley really has done a great job here pulling these components together.

The new SB Tactical PDW adjustable brace was available from Brownells and I picked that up in addition to a HiperFire EDT2 trigger which I knew from my experience with it on the MPX would ignite handgun rounds well. Brownells was also handy for all the other little parts such as grips, Bravo Company charging handle, and Glock magazines that turn this into a final project.

The SB Tactical PDW brace is a OEM product contracted through Maxim Defense and it is one of the sexist little arm braces you can use for a pistol. The SB Tactical PDW brace is not particularly light, but it is comfortable should you decide to now legally shoulder this arm brace. The brace also delivers all the usability you would want in a build like this without any downside with the exception of a weight premium over just a buffer tube.

Initially an Eotech was riding on top for sighting duty, but I wanted to drop weight where I could and opted for a light, rather outstanding and affordable Sig Sauer Romeo 5 Red Dot. Sig Sauer has come out of the gate hard and is delivering some of the best optic innovation, pricing, and quality I have seen in awhile. Hard to believe I was a skeptic of their optics line initially, but they are doing it all right. This little Romeo 5 delivers everything needed to hammer away beyond 100 yard on steel targets.

SOME TUNING REQUIRED & FUNCTIONALITY

During assemble and doing to initial bench function testing I was skeptical the light 360-degree feed ramp taper was sufficient around the barrel’s chamber to facilitate reliable feeding and I was right. Generally handgun ammo fed firearms need a lot of assistance getting the short and stubby rounds to feed perfectly. Handgun rounds can tend to bind and bobble easily without a lot of rigorous feeding guidance and this was the case here.

A Dremel with a small grinding wheel was used to relieve and round that squared taper into more of a rounded lip versus two angled edges meeting. A bit more of smoothing and then mirror polishing delivered a chamber and bit of a ramp that seemed to just suck rounds into it. Of note, I am experienced in this and willing to buy a new barrel if I jack it up - I recommend using a gunsmith for this modification. I have passed on this modification to Faxon who has noted they will look into my modification to increase out of the box reliability.

One other strange issue I had was a case that separated on some new factory loaded 10mm ammo, but I did not see any indications of separation or stress on any of the other cases. It was perhaps one of those break in issues, however the case was stuck in there pretty tight, so after removal I also polished the chamber with super fine polish and soft Dremel wheel. To date after a long break in this was the one and only issue I experienced like this.

Thousands of rounds later and I am confident that this little hammer thrower is more than reliable enough to use for defense or as a backup for predator hunting. On my last coyote hunt, my buddy jumped behind the ATN night vision rifle and I was left thinking a small AR15 pistol might be wise next time out if a coyote popped up in front of us. This would certainly do the trick.

FIT, FINISH, & FEEL

Thought this is a short little compact 10mm AR15 pistol it is not that heavy at 5.95 lbs empty and 6.7 lbs with a loaded magazine. It does feel hefty but even with 780 ft/lb loads it is a delight to shoot during extended shooting. This weight is right in the range of a Sig MPX so I was delighted given what is packed into this little pistol. The length measures 20-inches even and with the SB Tactical PDW brace extended the total length is 22.5-inches.

From a fit and finish perspective New Frontier and the rest of the vendors did a great job at finishing. The only fitment issue was the feeding tweaks noted above, but I have done that tweak several times on other handgun caliber carbine such as the Keltec Sub2000 to get feeding working perfectly and did not come as a surprise and was more of an expectation.

FINAL THOUGHTS

Personally I love that this little pistol delivers a ton of power in a very small compact size and it is a total blast to shoot. Of course many will ask why not an AR15 pistol, yep I have a few with barrels from 7.5-inches to 12-inches, but this rig is so much quieter than those guns and it also lacks the deafening ear bleeding boom and 3-foot fireball delivered from very short barreled AR15s - this sounds like a handgun… that’s it. The other note is that AR15s in .223 loose a lot of energy with barrels under 10-inches. Arguably this little pistol is still 3-inches shorter and likely delivers more energy than an AR15 pistol with a 7.5-inch barrel.

The build really seemed to have found a sweet spot that allows functioning with the neutered rounds as well as the full power rounds. Even the oddball Liberty Ammo worked with the shockingly light 60gr 10mm round screaming along at 2400 ftp and delivering a whopping 780 ft/lbs of energy. For defense, the Liberty Ammo is my go to round for 10mm personal defense. One the other side though you have rounds like the 650 ft/lb Federal Bonded 10mm round with a bonded hunting bullet that does what the 10mm round was intended to do and is an excellent choice for hunting hogs, deer, and coyote. The Buffalo Bore rounds fit someplace in the middle with a full hollow point 180gr bullet with 728 ft/lbs of energy. Even the inexpensive PPU rounds offered a lot of power for not a lot of cash.

Hopefully the 10mm is resurging again, but for me this little guy and my G29 and G20 are a great set of kit to handle almost any situation that be slipped into any pack.

SPECS

New Frontier Armory Upper and Lower Set

New Frontier Armory .40/10mm Carrier

KVP 10-oz Buffer

KVP Heavy Buffer Spring

KVP 4-inch 10mm Barrel

KVP Blast Redirecting Brake

KVP Carbon Fiber Forend

Glock G20 Magazines (G29 mags will work as well)

Sig Sauer Romeo 5 Red Dot

SB Tactical PDW Brace

Hiperfire EDT2 Trigger