(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.