By John Bibby
Short Distance
.300 Blackout
.300 Ham’r
.458 SOCOM
Medium Distance
6.5 Grendel
.277 Wolverine
The AR-15 is a hotbed of innovation for cartridges that can thread the needle between providing great terminal performance and staying within a very small case footprint. The tremendous number of attempts at this means there are lots of wildcat cartridges out there and at least one of them will do what you want. The downside is many of these choices have a brief moment in the sun, then wither on the vine.
A great example of this phenomenon would be the 6.8 SPC/6.8 SPCII. It began with tremendous fanfare; but due to a few design “errors” and newer options being “better,” it really isn’t a great option anymore. But at least the 6.8 got off the ground. There are tons of others that never see the light of day outside the niche environment of the wildcat community.
I will be discussing five choices for your AR that do quite well at either short or medium distances. Before we get into a disagreement regarding distance terms, long range starts at 600 yards. We will define short distance as 200 yards.
The first three we will discuss are certainly best used within the short distance envelope. These are .300 Blackout, .300 Ham’r and .458 SOCOM. Of these three, the .300 Ham’r has not proven its durability in the market as it has been available for least amount of time. The other two may be surpassed at some point, but both have a dedicated following and have proven themselves with multiple factory options available.
Dedicated magazines are a good idea for any alternative AR cartridges, if for no other reason than to not accidentally run them in a gun chambered for something else.
.300 Blackout
This cartridge is one of the easiest to convert a standard 5.56 AR to shoot. A barrel swap is the only mandatory item. The cartridge was originally built from necked up 5.56 cases; but now, purpose-built brass is plentiful and cheap. Factory ammunition comes in many options from 220 gr subsonic rounds down to 110 gr supersonic rounds. Subsonic hunting choices are best used inside of 75-100 yards. This reduces the need to adjust for drop and helps to keep the rounds in their expansion envelope.
Supersonic options typically run from 110 to 125 gr. They are on the lower end of the .30-30 power envelope. The bullets travel a few hundred feet per second faster than the typical 150 gr bullets of a .30-30 which makes for a flatter trajectory and slightly longer range with similar hitting power.
.300 Ham’r
This is a “better” .308 cartridge than the .300 Blackout; but “better” comes with huge caveats. As with all things in life, especially alternative AR cartridges, there is a huge trade off here. It is also a barrel-only swap and for supersonic bullets from a rifle barrel, it pushes the same bullet 200-400 fps faster than a .300 BLK. But that makes the assumption you never want to run subsonic or in a pistol configuration. The .300 Ham’r must have at least a 16” barrel to make the better velocities and the round’s advantages drop precipitously with any shortening of the barrel.
Having said that, 2300 fps for a 150 gr .308 bullet (1750 #/ft ME); out of an AR-15 isn’t something to sneeze at.
.458 SOCOM
When you absolutely positively need to plant something right there, right now; .458 SOCOM is a great choice. You do need that thing to be pretty close though. Where the 300 Ham’r provides 150gr bullets at 2300 fps, the .458 SOCOM has options from 250 gr at 2150 fps to 450 gr at 1500 fps. Most of these supersonic options are close to 2500 #/ft of muzzle energy. That amount of energy coupled with almost half an inch of initial diameter that expands to well beyond 0.75,” is a potent force. The other advantage is most of that energy is expended in the target, unlike 5.56 that tend to knife through while still retaining a lot of energy after exiting.
There are also 500 and 600 gr subsonic options. By definition, these are below 1100 fps, but still pack a wallop.
The three downsides to this caliber are strong recoil, lots of proprietary parts and being anything but flat shooting. ARs are not exactly heavy guns. A heavy bullet moving moderately quickly out of a light gun, creates strong recoil. With a 458 build, the bolt assembly, barrel must be changed, and an enlarged ejection port is quite helpful. As far as trajectory goes; one example with a 75-yard zero, the bullet is an inch low at 100 yards, almost 5” low at 150 and almost 14” low at 200. More importantly, at 200 yards the retained energy is below 900 #/ft. Such a low energy level defeats much of the purpose of this cartridge.
The medium-distance cartridges to look at are as follows:
6.5 Grendel
Some people like to look at the Grendel as the little brother of the 6.5 Creedmoor; but that is unfair. They really don’t have much in common other than the 6.5mm diameter bullet. This cartridge was designed for hunting and paper punching out to 800 yards from an AR-15.
Factory ammo choices for the Grendel run from 90-129 grains. Most reloaders stay in that same range as velocities drop precipitously with 140+ gr bullets. A very standard hunting load is a 123-gr bullet traveling at roughly 2400 fps in an 18-20” gun. This provides a muzzle energy of 1800 #/ft and a retained energy of just over 900 #/ft at 350 yards. This means most hunters will not take shots on medium game beyond that range. That being said, most hunters are more concerned about their ability to consistently hit at distances past 300 yards. Because of this, most hunters are not limited by the energy drop of the round. For those who are, they are not hunting with a modern sport rifle (AR).
With paper punching. That same load, despite having a .506 BC is entering the transonic zone at 800 yards and has over 260” of drop. For comparison sake this is still significantly better than a 77 gr 5.56 that enters transonic at least 100 yards earlier and has almost 290” of drop at 800 yards.
.277 Wolverine
This cartridge is a wildcat, so factory ammo really isn’t available although a few boutique shops do load it. I included this cartridge as it is most of the things the 6.8 SPC wanted to be and many people are having great experiences with this option.
Unlike the 6.8 SPCII, which requires a different bolt, the .277 Wolverine is just like the .300 BLK and .300 Ham’r in being mil-spec bolt friendly. With a simple barrel swap, you have the ability to use .270/6.8mm bullets out of a reshaped 5.56 brass. The brass is shortened to 39 mm, the neck is lengthened, and the shoulder is adjusted to a 23-degree angle in the forming process. These adjustments provide reliable magazine feeding of the longer .270 bullets.
Typically, the heavier bullets are 110 gr running at 2500 fps from a 16” barrel. This provides a muzzle energy of just over 1500 #/ft and at 250 yards a retained energy of 940 #/ft. You give up a little velocity and retained energy in comparison to the 6.8 SPC II. The slight velocity drop comes with not needing a special bolt, brass or magazines. In my mind, this makes the .277 Wolverine a better choice and seeing as factory support is drying up for the 6.8 variants, it may soon revert to wildcat status anyway.
