Rambling Thoughts on Cartridges for the Modern Sporting Rifle
By Greg Ritchie

Brown Writing implement Ammunition Amber Bullet

[.22 Nosler (left) - .223 Remington (right); Photograph under Creative Commons]

I have had a fairly long history with the AR style rifle, mostly negative. Starting with my USMC days. For reasons we will not discuss here, I learned to hate he thing. Suffice it to say unreliable in my experience.

Through the years I maintained that view, prided myself in that I just needed to put that one bullet from my beloved single shot rifles where they needed to be. I still shot the AR's, tinkered with them some, saw the malfunctions they had and continued to dismiss them.

However, going on six years now I have been an AR owner. I admit to the purchase being a political decision. Bought just because I still could. It was destined to be a safe queen. But two things happened. First, it was reliable, second, it was accurate. Accurate rifles are interesting.

All this to make my point. My look at the AR platform is still jaundiced. I think it is designed around a specific cartridge and deviate very far from it's basic design parameters you are asking for trouble. Also my focus is on performance and accuracy. With one exception, all my Modern Sporting Rfles have heavy barrels between 18 and 24 inches in length. Finally, the AR-15 platform and it's cartridges are suitable for varmints, deer, and feral hogs. Maybe antelope, but not moose, black bear, or elk except for one exception. There are better platforms and cartridges. Finally, l looked at barrels that could be bought economically with reloding dies that are readily available and economical as well.

So knowing that more than a few will disagree with me, let's take a look at what I think are the best hunting cartridges / chamberings for the platform.

5.56x45, 223 Remington, 223 Wylde, 22 Nosler.
The 5.56 is what the platform was designed around. Other than that, I would leave this chambering alone. With it's long and oversized leade, it's seldom as accurate as the other cartridges compared with here.

The 223 Remington is a good one and one of my favorites. Matter of fact my dies in this caliber are set up for optimal length in my 223 Remington single shot rifle. Of course my single shot only gets handloads. If you were only going to shoot 223 Remington you are good to go, but I think there is a better option.

The 223 Wylde. This chambering has the long leade of the 5.56, but the leade has the diameter of the 223 Remington. This is the best of both worlds. The tighter bore helps to keep the bullet concentric when it engages the rifling, but the length of the leade allows you to shoot the higher pressure 5.56 rounds if you desire too. It is a very accurate chambering.

The 22 Nosler. 22-250 ballistics out of the MSR. What's not to like? How about case head swipe. This cartridge shows pressure signs. Even in factory loads. Load it down to where the pressure signs disappear and you are back in 223 Remington territory. To be fair, I believe this is due to case head design. It is squared off around the perimeter of the rim. I understand that the new cases are beveled and this has corrected the problem. Too little too late for me. I have removed the 22 Nosler from my upper and put the 223 Wylde barrel back on. The 22 Nosler has a rebated rim as well. It uses a 5.56 rim, but a 6.8 case. I think Nosler probably should have gone with a 6.8 case head size. You have to change the magazine anyway, why not the bolt as well, but then you are getting away from the standards the platform was designed around.

.277 Wolverine, 300 Blackout, 7.62x39
Let's get the 7.62x39 out of the way first. It's a good cartridge but a poor choice for the MSR. It's about as far as you can get from what the platform and still have a chambering that works...sometimes...maybe. This cartridge has a poor track record in the platform with broken bolts and cycling issues. The 7.62x39 requires a non standard bolt and magazines.

The 300 Blackout is a good one though. One of my favorites. But it is, in my opinion, a bit overrated. Excellent subsonic with the heavier bullets, but the heavy for caliber bullets do not typically expand well. They do not make good hunting bullets. It's a much better game getter at supersonic speeds. The 110 grain Barnes Blacktip bullet at about 2400 fps is the Blackout load that all others are compared to. My favorite is the Sierra 125 grain Pro Hunter though. At just over 2200 fps, it is my choice for a woods carbine where my shots will likely be 100 yards or less. I think this cartridge is at it's best at yardages under 150 yards. This, by the way, is the exception to my preference for longer barrels. It wears a 16" tube. Matter of fact, you will be hard pressed to find a barrel longer than 16" for the 300 BLK, and if you did performance would likely suffer due to bullet drag in the barrel, the powder having burned well before it hits even the 16" mark. The 300 BLK uses standard magazines and bolts.

The .277 Wolverine is in my opinion probably the best all around cartridge for the AR-15 MSR. The .277 WLV will push a 110 grain bullet out of an 18" barrel a full 300 feet per second faster than the 300 BLK will push it's 125 grain bullet and will extend the effective hunting range at least 100 yards over it's .308 caliber counterpart. It will push the lighter bullets fast enough to be effective on varmints and will operate subsonic with the heavier bullets. The Wolverine is available with both a 1:11 and a 1:7 twist barrel. It uses a standard bolt and magazine. One mark against the .277 WLV is it is not a SAAMI cartridge, but there is factory ammunition available from a handful of boutique ammunition manufacturers and brass is available from Starline. But like the 300 BLK, .277 WLV brass is easily formed from 223/5.56 brass.

25-45 Sharps, 6.8 SPC, 6.5 Grendel
My choice here was easy. The 25-45 Sharps. It uses standard bolts and magazines. But there were a few of issues. 75 and 87 grain bullets worked fine, but if you wanted to use the heavier 100 to 120 grain bullets the ogive of the bullets intruded into the mouth of the case. I never could duplicate the velocity figures quoted, I was always off by 100 to 200 feet per second. And my barrel just was not accurate. I could get 1 1/4 to 1 1/2" groups at 100 yards if I held my mouth just right and the moon and stars were aligned, but normally I shot 2" or larger groups with it. A shame really. If I could get the accuracy and shoot 100 grain bullets this would be the ultimate all around cartridge for the MSR I think.

The 6.8 SPC takes non standard bolts and magazines but I like the shape of the case for the semi automatic platform. I while I think it's a good choice, and it's not going away anytime soon, I also think it's a dying cartridge so I passed it up.

The 6.5 Grendel also uses non-standard bolts and magazines. I also do not like the shape of the case for feeding in a semi automatic. But I do like the 6.5mm /.284 bullet. And I like the fact that the 6mm PPC, the Grendel 1st cousin, is an extremely accurate cartridge. While there are stories of feeding issues with this cartridge, I have not experienced any. Also, the velocity figures are a bit optimistic (although most figures are taken from a 24" barrel and mine is only 20 inches). The accuracy is outstanding. Seldom do groups go over 1 inch. The norm is about 3/4 inch, ant I have shot enough 1/2 inch groups that you can't call them uncommon. I use the Sierra 85 grain and 100 grain varminter bullets. Even though it uses a non standard bolt and magazine, I have had no problems. I do however, keep a spare bolt handy. Plus I use the short 4 round magazines which suffice my needs and I believe are more reliable. I have come to really like this chambering

450 Bushmaster, 458 SOCOM, 50 Beowulf
I want one of these just because. I prefer the 458 SOCOM I think, and one has been on the back burner a while now. I doubt either of these cartridges will ever happen though. If it does it will likely be the 450 Bushmaster. Components for the 50 Beowulf are just too hard to find. 458 SOCOM while easier to find, is not too far behind the Beowulf. The 450 Bushmaster, both factory rounds and components are much easier to find. That the Bushmaster uses .452 bullets is considered detrimental by some, I think just may be an advantage. It would definitely make a good woods rifle for deer and hogs. These cartridges are the exception I spoke about earlier. With either of these chambering I would add moose and black bear to the list of animals that the AR-15 MSR is capable of cleanly taking. I would want the 458 SOCOM for elk though.