WMD Guns .300 Blackout

When a whisper isn’t a Kaboom!
; .

Lancer Systems lower receiver was used as the foundation.

One thing making the AR-15 platform so popular is its modularity — you can mix, match and accessorize your rifle to your heart’s content. It’s like Barbie for men!

I have exactly one AR that has not been “customized” in some way — an original Colt SP-1. For a while, I replaced the Delta rings with round ones so I could add a quad rail to it but nothing else was changed. Out of nostalgia more than anything else, I went back to the original triangular handguards.

Several years back I had a rifle chambered in .300 BLK. I reload for every caliber I own and after much deliberation decided I didn’t want to add another and sold the rifle. I’ve regretted the decision ever since.

Having several completed lowers sitting around, I decided to turn one of them into a .300 BLK.

I decided to use Lancer Systems’ lower for the “build.” The unique thing about this receiver is there is a takedown pin at the bottom of the trigger guard allowing for different sizes of funnel-type magazine wells. I used the medium size, as it offers a quick reload without becoming too bulky.


Completed rifle equipped as evaluated. Denny likes the classic two-tone look.

WMD Guns To The Rescue

I contacted WMD Guns about receiving one of their excellent uppers for the project. Wynn Atterbury of WMD was enthused about the project and agreed to send one to me. I received the upper receiver within two weeks.

The forged upper receiver has a 16″ barrel and is fitted with a 15″ M-LOK handguard. The rifle has a mid-length gas system. The top rail runs from the rear of the receiver to within an inch of the muzzle with a total of 56 M-LOK slots so there’s plenty of real estate for a wide variety of accessories. A brake attached to the muzzle has three large slots on each side and three holes at 12 o’clock.

The upper features WMD’s proprietary NiB-X (Nickel Boron eXtreme) finish. This coating is tougher than hard chrome with a coefficient of friction near Teflon with excellent lubricity. This coating requires little wet lubrication and so it cleans easily after shooting, while protecting against the elements.

NiB-X is offered in a matte silver/gray appearance, distressed, or polished to a near chrome look. I opted for the matte silver/gray finish. It gives the rifle a classic two-tone look and is fairly unique for an AR-15-type rifle. I personally find it aesthetically pleasing.


A Brief History

The inimitable J.D. Jones, while working under S.S.K. Industries (a company he started), invented the .300 Whisper caliber in 1992 as a wildcat cartridge. The parent case Jones used to make the .300 Whisper was the .221 Remington Fireball necked up to accept .30 caliber bullets. The end game was to use a heavy bullet traveling at subsonic velocities with a silencer.

The .221 Remington Fireball is identical to the .223 Remington except the .223 is longer and uses more powder. By doing this, the .300 Whisper in an AR-15 platform can use the same bolt-carrier group and magazines as a standard 5.56mm/.223 Rem rifle.

Now look at the more recent and commonly known .300 AAC Blackout (.300 BLK). The caliber’s name partly comes from the company that “invented” it — Advanced Armament Corporation (AAC). So what is the difference between .300 AAC Blackout and the synonymous .300 Whisper? Without boring the reader with things like the measurement of the barrel throat, etc., the answer is not much really.

The largest difference is the .300 Whisper started as a wildcat round and AAC went to the trouble of getting the cartridge recognized by the Sporting Arms and Ammunition Manufacturers’ Institute (SAAMI) as a standard round.

As a sad side note, J.D. Jones never received any royalties and little recognition for his efforts. Partly in homage to J.D., Black Hills Ammunition lists the cartridge as the .300 Blackout/Whisper.

So much for the history lesson.


WMD Guns upper receiver has their proprietary NiB-X finish with a matte silver/gray appearance.

Avoid The Kaboom!

The .300 BLK cartridge will chamber in a 5.56 rifle, but in no way, shape or form should you ever try to fire it. The .22-caliber bore simply isn’t big enough to handle the .30-caliber projectile of the .300 BLK round and all that pressure needs to go somewhere once the primer is struck — the results can be devastating.

When I had my first .300 BLK rifle I avoided this by using only Lancer magazines — both the original and Advanced War Fighter — in the rifle. I have never placed a 5.56 round in them or a .300 BLK round in any other AR mag.

I can almost hear someone saying, “Just pay attention to what ammo you’re putting in the gun.” I agree with this in a perfect world but I often shoot with family members, including grandchildren, where there are probably three or four ARs on the range. Using a noticeably different magazine minimizes the chance of a kaboom.


Range Time

I attached an Aimpoint Micro T-2 to the top rail. The T-2 has a 2 MOA dot so it covers 2″ at 100 yards, 4″ at 200 yards and 6″ at 300 yards. This suits me fine as I rarely, if ever, shoot farther with anything but a precision rifle.

The “trick” to shooting smaller groups with a red dot sight (RDS) is to lower the intensity. While this doesn’t actually change the size of the dot, it gives the illusion of a smaller dot for greater accuracy.

I went with the ammo I had on hand for the .300 Blackout, the Black Hills Ammunition 125-grain TMK (Tipped Match King). This load develops 2,100 feet-per-second and 1,224 foot-pounds of energy at the muzzle.

I obtained a rough zero at 50 yards and then fine-tuned the T-2 at 100 yards.

Shooting from the bench, I shot four 3-round strings. My best group measured 1.5″ while the average group size was 1.8″. Not too shabby for my first time out and using an RDS instead of a conventional riflescope.

I found the muzzle brake to be quite effective though, like all brakes, very loud.



I don’t have a .30 caliber suppressor at the moment, but I plan to resolve the problem in the near future to fully utilize the potential of the .300 BLK.

WMD not only offers parts and assemblies, but entire guns and NiB-X coatings.

Whether you are looking to assemble your own or purchase an entire gun, check out WMD Guns. You won’t be disappointed.

Purchase A PDF Download Of The GUNS Magazine April 2022 Issue Now!



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