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Cartridges for the MSR

619 Views 4 Replies 3 Participants Last post by  ajole
(Spin-off from @lklawson and his 6mm ARC thread)

Just a look into cartridges I have tried , or have developed a great interest in for the AR-15 platform.

first and foremost is the 223 Remington. After all its the cartridge the platform was designed around. I know - the M16 was designed around the 5.56 NATO, but I am going to call it the 223. This also brings up a peeve of mine. The AR 15 is designed around the .378 rim diameter. The bolt in the AR rifle is a known wear part and prone to breakage. But back to the 223 Remington. This is a fine varmint cartridge, good to around 300 yards and a bit more. Some say adequate for deer. I say it is adequate for deer in the hands of a patient and careful marksman.

22 Nosler. I picked this cartridge over the 224 Valkyrie for 2 reasons, the slower twist rate and the rebated rim, giving me that rim diameter I desire. Intent was 22-250 ballistics out of the MSR. This was accomplished, but with a minor problem. It ate up the rim. I also found my example to be hard on barrels. But this is a good choice for the groundhog hunter who wants to use the MSR platform. With Benchmark and Varget powders, I was able to best 3500 fps with the Hornady 52 grain A-Max.

277 Wolverine. I never got any further than owning the barrel on this one. But i have shot the 277 WLV quite a bit. I think this is a better cartridge for deer and feral pigs than my 300 BLK. I keep threating to build a 277 WLV WLV of my very own, just have not gotten around to it.

300 Blackout. I have had a long history with this cartridge if you count the 300 Whisper as history. Used a rimmed version called the Whisp-R in a single shot pistol. The biggest difference in the cartridges is rifling twist. 1:10 for the Whisper, 1:7 for the Blackout. I never intended for my rifles to be suppressed, but supersonic for hunting the eastern woods. The cartridge has become one of my favorites.

25/45 Sharps. This is a cartridge that I wanted to love. Its biggest drawback is its inability to shoot conventional bullets heavier than 87 grains. It would of been better had the Sharps Company had used the 25/223 wildcat which shortens the neck by .050 which allows the use of the 100 to 120 grain bullets. Still, it is a viable cartridge and if i were to ever build a cartridge that i got rid of, it would be the 25/45 Sharps.

6.5 Grendel. I do not like the fact that this cartridge requires a non-standard bolt, but that is a small price to pay if you are wanting a cartridge that will best the 223 Remington. I thought the cartridge was velocity challenged though. I built mine with a long heavy barrel ang could push the 120 grain bullet to over 2400 fps. but the drawback was a heavy unweildy rifle that was not really fun to carry.

450 Bushmaster. Another non-standard bolt, but sometimes you just got to have a Thumper. Poison on deer and feral pigs. I dont use mine much, its pretty violent to shoot. Interesting that the Ruger Ranch Rifle in 450 BM is the only in the line-up that comes factory with a muzzle break. The recoil is pretty stout, I would not want to shoot mine without it.

350 Legend. What can I say. I want to hate this cartridge. But it has become my favorite for game larger that varmints. If I could only have 1 MSR, this would be it, along with a second upper in 223 Remington.

6mm ARC. This is what I intended to replace my 6.5 Grendel with. But my reading tells me that this cartridge comes with a lot of baggage. Read what the manufacturer puts out and the cartridge is the best thing since sliced bread, But I understand that it is plagued with the sane issues the 25/45 Sharps has. The jury is out and I am waiting on a verdict. I do think this cartridge ha the potential to be the perfect dual-purpose cartridge for the MSR. We will see.
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Well…actually……..you were right, the M16 was built on the .223 Rem.

The original non AR10 Stoner rifle , the AR15, was designed to use the .222 Special, a modified .222 Remington with different powder loads which was renamed as .223 Remington. The CAR15 was also .223 Rem.

In 1963, the Army bought the first M16’s, after having renamed the .223 Remington as 5.56 mm Ball, M193. But it was still just .223 Rem.

Then in the late ‘70’s, the military developed a “not” .223 Remington bullet that was adopted in 1980 as what we now call 5.56x45 NATO, M855, or some SS something or other.
SS109 developed by the Belgians at FN Herstal. 62 grains.

Anyways. I have a .223 Wylde chambered AR in 16" flavor, and my 6.5 Grendel pet in 12" just for shits n giggles.... though from a similar sized barrel; the 6.5 beats the 5.56 ballistically in terms of energy and range. Next potential project depending on income would be either a 6.5 or 5.56 20" A4 semi clone with fixed stock and bog standard flat top receiver to accept whatever optics I decide on eventually. Leaning towards 5.56 simply for its availability compared to any other AR15 cartridge.

Edit. I'm really curious what if I get handloads 6.5s in the lightest 6.5 bullet possible, and compare to the same gr sized 5.56, see if theres real merit to 6.5 doing better for its size and case capacities.. the lightest factory loads I can find and buy now; 100gr Wolf. Otherwise its 123gr.

There's Barnes 85gr 5.56 ammo, then theres Sierra's 85gr 6.5 bullets.
Don’t bother. The entire purpose of shooting 6.5 was shooting heavier bullets.
There is no merit to using it to make 5.56 weight bullets go faster…that’s what .224 Valkyrie or .22 Nosler was for, and it had a few 90 grain loads that were not that fast, but heavier than 5.56 would usually push at any decent velocity.
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