High Caliber Sales is known for milspec uppers, such as this MK18 Mod1, that can be run hard with full expectation of years of service.

When the military needs to retask a weapon, component, or even design something new, they turn to places like the Naval Surface Warfare Center (NSWC) in Crane, Indiana.

Over the years, Crane has had a hand in the development of many different war-fighting tools. Some of the most famous have been AR-15 variants that have come to be used by special forces in operations the world over.


When my buddy and fellow gun writer Sean Utley and I were discussing plans for an upcoming class, Sean mentioned that he’d found out about a company called High Caliber Sales (HCS), LLC in Carmel, Indiana that was making authentic MK12, 13, and 18 variants.

At the SHOT Show, we met up with the owners of the company. Kevin O’Neill and Alan Brown have been in the firearms field for many years and are on the inside of an exclusive industry where knowing the right people is almost as important as knowing the right skills.

The point man for HCS is Kevin O’Neill, whom I found to be a kindred spirit. The man eats, sleeps and breathes shooting. He has trained with some of the world’s most renowned trainers and is dialed into the firearms industry with a quiet professionalism.

The other half of HCS is Alan Brown, a true gunsmith of the sort that never stops improving on his craft. In his previous life in service to our nation, he worked at NSWC Crane for 22 years and helped develop the weapons that would eventually be known as the MK12, MK13 and MK18.

In an astute choice to turn a lifelong dedication to craftsmanship into a business, Kevin and Alan started High Caliber Sales. As is the case when manufacturing meets demand, HCS has become highly sought after in the market for authentic uppers.

These are not cosmetic reproductions but true milspec pieces that are made by the very people who helped develop these weapons for our military. HCS reaches out to those who are currently making parts for Uncle Sam and has them making parts for your gun. As I said, authentic.

Sean Utley works barriers during full-auto drill on the move.


I have always been partial to the AR- 15 platform and tend to lean toward a rather homogenous set up with my ARs. The MK12, being an AR-15 variant, appeals to me because at its base level it is an AR-15, albeit a big one. However, its considerable length and weight are completely irrelevant seeing as how it is a rifle that’s meant to be fired from a stabilized position instead of on the move.

MK18 has a solid reputation for reliability and mobility. Its 10.3-inch LMT barrel is just long enough to deliver the goods out to 500 yards. But it’s still short enough that CQB tasks can be executed with little drag on the operator.

I have fired various precision rifles over the years and can say I’ve found nothing that draws my attention like an MK12. With a Nightforce Optics scope, Black Hills MK262 77-grain ammunition and a steady hand, there is little in the way of man or machine that can’t be destroyed by an MK12 from as far out as 600 yards. It is the epitome of versatility.


For this article, I was fortunate to work with Kevin’s personal MK12 Mod1. While I normally jump on a new gun as soon as it arrives, I was forced to wait for trigger time on this one due to a week of nonstop rain at my home in Tennessee.

With only one day left before I had to put the gun in a box and ship it back to Kevin, I finally gave up on the weather and went to Plan B.

I went upstairs to my master bedroom, which overlooks my two-acre range. I popped the window screen out, placed the Harris bipod on the windowsill, covered my head and shoulders with a shemagh, and settled down to a little scanning and reading of the wind. Relaxed in my cheek weld behind the scope, I would shift into a new field of view with the slightest movement of the full A2 buttstock.

I soon found one of the soup cans my son and I had been plinking at a week prior. From about 125 yards and two stories up, I held my appropriate zero on the base of the small can and squeezed off a round. With the Ops Inc. 12th model suppressor firmly in place, there was no flash or muzzle rise. The recoil was almost nonexistent, which allowed me to stay on target relatively well. I watched a slightly blurred image as the soup can went airborne in the rain. I found where it landed and hit it again—and again.

After completely obliterating the soup can, I scanned over the range and acquired one of my steel targets through the canopy of a stand of trees below me and about 75 yards downrange. The steel was another 50 yards farther down, but I knew the Black Hills ammo I was shooting would deliver a solid hit even through the treetops.

I steadied my position by reaching forward and grabbing the windowsill. As the fog rolled in, I rang the steel with a chuckle. I was really diggin’ this rifle. I finished off with a mad series of shots across the width of my range, hitting anything I could find in the Nightforce 2.5-10X24 NXS.

High Caliber MK12 Mod1 with Ops Inc. 12th model suppressor is a formidable weapon.

Mostly I was trying to overheat the barrel to see if the zero would shift noticeably. It didn’t. Most of what I shot at I hit the first time out. That’s really saying something about the gun and the scope, because it was pouring rain and the fog was fairly thick. With the suppressor, even without hearing pro, I was comfortable with the report of the muzzle.

With proper foliage and a shemagh to break up the human form, it’s very hard to see an operator behind an MK12.

As I collected brass from my bedroom floor, I realized that searching for my position in a war zone, in like conditions, would have been all but impossible. With this sort of set up, I would have almost zero signature at long range.


Getting my hands on an MK18 from HCS proved to be difficult due to the fact that they’re in such high demand. Instead I’ll base my comments on my first-hand witnessing of an HCS MK18 being run hard at two separate rifle classes.

Sean Utley had obtained a highly coveted HCS MK18 Mod1 upper and ran it beside me at a tactical carbine class on his select-fire LMT lower. A few months later, his wife ran the same gun beside my wife at a class where Sean and I were guest instructors.

I never saw this MK18 take a dump— not once. I verified this with Sean to be certain I was reporting this correctly. It ran consistently, and even when it was pushed in full auto, it cycled each and every time the trigger was pulled.

At one point, Sean and I ran a barrier drill where we were required to keep up our rate of fire while alternating our cover. Sean ran the MK18 until it was too hot to touch, but it never failed. He ran it dry before realizing that it needed lube, and still it didn’t fail.

HCS uses components from Knight’s Armament, PRI, Daniel Defense, Douglas Barrels, and various other manufacturers of milspec components. Douglas’ 1:7 chrome-lined 10.3-inch barrels are true to specs and come from the same manufacturer that turns barrels for Crane, so you can trust they’re being done right.

Whether you’re buying a Mod0 or Mod1, both come properly torqued and mated to a flattop upper with an MPI full-auto bolt carrier group and PRI gas buster charging handle.

You can order several upgrades for your MK18, so it pays to read each option carefully and get what you want the first time out. HCS won’t skimp on your build, and I suggest that you don’t short yourself in settling for anything less than what you want. It’s better to save up for what you want than fix a “bargain” gun later.


At this time, High Caliber Sales is only producing MK12 and MK18 uppers. The only complete gun that they currently make is the MK13. While this may seem like a point of contention, it is actually an astute business decision. Anyone who deals in guns knows that there is little money in lowers. The ATF paperwork is a pain in the neck and the profit margin is low.

HCS concentrates on making highquality uppers that you can mate up to your lower of choice to complete your dream rifle.

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