Rambling Thoughts on Alternative Cartridges I Have Tried in the AR-15
by Greg Ritchie

The 5.56 is the quintessential cartridge for the AR-15, but sometimes you just want more. Here are some I tried and my thoughts on them.
[5.56x45mm NATO, photo by Francis Flinch, Creative Commons Attribution .30 Unported]

My first attempt to better the AR-15 and the 5.56 was the 6x45. Simply neck the 5.56 case up to take a .243 bullet. There is lots of love for this cartridge and I had great expectations for it. It operates at the same pressures as the 5.56, but the pressure has a larger base to work with than with the 5.56. the end result is you essentially get a larger bullet that's about 10 grains heaver at the same velocity than you get with the 5.56. The issue I had with my example is it just would not shoot the heavier bullets. It liked the 75 grain bullets, but start getting heavier and accuracy just fell apart. I did not consider it a good deer cartridge and felt the 5.56 was just as good for varmints.


[By Peter Gnanapragasam - Own work, CC BY-SA 3.0]

My second attempt was the 300 Blackout. I like this round. Matter of fact, I have three rifles in this caliber. I do not consider this a 300 yard rifle. In my opinion, 200 yards on CPX2 game is max and 150 yards is more reasonable. I have shot everything from 110 grain jacketed to 245 grain cast. All have shot reasonably well, some have shot excellent. I would recommend the 300 BLK to anyone who wanted an AR to use in open hardwoods. I would be wary of the subsonic rounds, but supersonic bullets from 110 grains to 135 grains will serve you well.

My third attempt was the .277 Wolverine. Actually I sold the barrel and reloading dies for more than I paid for them. I didn't realize that the cost of the barrels had gone up! But the rifle is close, and I have shot it quite a bit. I have only fired the 110 grain bullet. It does an honest 2500 fps, faster than I can fire the 110 grain bullet out of the 300 BLK. Plus the .277 bullet holds up well. It is accurate to boot. 3 shot cloverleaf groups at 100 yards are the norm from a rest. The .277 WLV was touted as almost 6.8 SPC and almost 300 BLK. I think that's why I let it go so easily. I used the money to try the next cartridge on my list. In retrospect, I actually like the .277 WLV better than the 300 BLK as a supersonic round and wish I had kept it.


[.277 Wolverine from JB's FIREARMS, LLC.]

This brings me to the next cartridge on my list, the 25x45 Sharps. I have always been a fan of the quarter bore. The .257 bullet is really a pretty sleek bullet. The 25x45 Sharps is supposed to mimic the 250/3000 Savage. An 87 grain bullet at 3000 feet per second. I never could reach the 3000 fps mark, falling some 75 to 100 feet per second short. Still, 2900 feet per second is not bad! I probably would have stopped there except for one thing. I never could get my 25x45 Sharps to shoot into an inch or less. Most everything would shoot into 1 1/4 inch at 100 yards. But I wanted no less than an inch.


[25-45 Sharps - Sharps Rifle Company]

My next cartridge was the 7.62x39. Not to better the Sharps, but just to see if I could make it work. I bought a barrel on sale for less than $70. Slapped it on a used upper receiver I had, bought a couple of 10 and 30 round magazines and gave it a try. I had heard they didn't run well, and mine did not. I finally got it to running well by enlarging the gas port and turning down the M4 feed ramps to a single feed ramp.


[7.62x39 By Malis - Public Domain]

My last attempt at an alternative cartridge for the AR-15 was an attempt to better the 25x45 Sharps. The 6.5 Grendel. Did I succeed? Yes and no. I am liking the 6.5 Grendel. It's definitely accurate. But velocity is low. It really needs a 24 inch barrel, I just don't want a barrel that long. I like the Sierra 100 grain varmiter bullet. I am pushing this at a little over 2600 fps using CFE223. This combination gets me just over 1/2 inch at 100 yards from a rest. I think I will keep this one until the barrel wears out. But, I don't like the cartridge in the AR15. It belongs in a mini action bolt rifle. I have not had problems with it in my AR, but there are lots of reports of feeding issues. To me it just does not seem right. On a side note. I have a 6.5 Arisaka. It has the reputation of being a weak round, good for a couple of hundred yards on deer. But it shoots a 129 grain bullet just as fast as the Grendel shoots a 100 grain bullet!


[6.5 Grendel 123 gr SST from Hornady]

In the end, considering what I have used, what do I like? Well, accurate rifles are interesting. I have already said I will keep the 6.5 Grendel until accuracy falls off, and I stand by that statement. But what would I recommend? First of a 5.56 or a 223 Wylde will be a primary for the foreseeable future. The 300 BLK for subsonic, or really just an all around carbine. The .277 WLV will get the nod for a supersonic larger than .223 rifle.