I have a .308, .223, 300Blk, and 9mm AR pistols. The 9mm is hands down my favorite I have more rds through it than the others combined. The .308 with a 10.5 barrel is an awesome novelity when family and friends come over but that's all it comes out for kinda like a .500 Alaskan. I'm not real familiar with 6.5 grendel but if it's like the .308 I would build the upper that lets you take full advantage of the rounds capabilities.
I did something similar recently with a few lowers I picked up. It all depends on what you want to use them for and what type of shooting you enjoy most.
As far as the short barrel builds go, they are handy. They have a certain sex appeal too I suppose. But unless you have a can, they aren't too cool to shoot. I've built 3 "commando" length builds. 2x 556 and a 300blk, all with either 10.5" or 11.5" barrels. They have a purpose, close quarters. Without a can, they can be pretty rough in those "close" quarters. Firing one without a can inside a house/room/indoors is about equivalent to a flashbang. After trying mine out in close quarters I quickly sold them off in favor of 14.5" and 16" barrels. Just too much blast and concussion for a couple inches of space savings. Plus the accuracy wasn't great. Was actually barely acceptable really. I only have one short barreled rig now and it's a 7.5" 300blk which I'll be putting a can on. Personally I wouldnt go below 14.5" unless making room for a suppressor.
I like shooting accurately though. I went through the short barrel phase. Now I'm going the other way, 20" plus. The 6.5 grendel is an awesome cartridge. It is a great accurate round and doubles as a decent defensive round. Good thing about ARs right now is parts are plentiful and relatively cheap. If you build something and it doesn't fit your needs, sell it and move on from there until you figure out what fits your needs. I like 300blk too, runs good in short barrels with pistol length gas systems. Subsonic with a can is crazy quiet.
As far as the short barrel builds go, they are handy. They have a certain sex appeal too I suppose. But unless you have a can, they aren't too cool to shoot. I've built 3 "commando" length builds. 2x 556 and a 300blk, all with either 10.5" or 11.5" barrels. They have a purpose, close quarters. Without a can, they can be pretty rough in those "close" quarters. Firing one without a can inside a house/room/indoors is about equivalent to a flashbang. After trying mine out in close quarters I quickly sold them off in favor of 14.5" and 16" barrels. Just too much blast and concussion for a couple inches of space savings. Plus the accuracy wasn't great. Was actually barely acceptable really. I only have one short barreled rig now and it's a 7.5" 300blk which I'll be putting a can on. Personally I wouldnt go below 14.5" unless making room for a suppressor.
I like shooting accurately though. I went through the short barrel phase. Now I'm going the other way, 20" plus. The 6.5 grendel is an awesome cartridge. It is a great accurate round and doubles as a decent defensive round. Good thing about ARs right now is parts are plentiful and relatively cheap. If you build something and it doesn't fit your needs, sell it and move on from there until you figure out what fits your needs. I like 300blk too, runs good in short barrels with pistol length gas systems. Subsonic with a can is crazy quiet.
Here's the thing; I don't believe in putting different chamberings into an AR from what it was designed for. Cycling issues would be my main concern, I've seen some with my Buddy's 300BO and 9mm AR's.
For a Pistol Caliber Carbine, I'd rather get the Ruger PC Carbine and be done with it. It is a caliber-specific design, inexpensive, the reviews are great, and rumors suggest possible additional later offerings in 45ACP, and maybe..., maybe a 40cal. Mine is on order and will be sharing 17rd magazines with my Ruger American Pistol 9 Pro.
If you can't find a versatile selection of .223/5.56 ammunition for your AR, I'd look a little harder; either that, or maybe you're asking more from the system than it's really going to be good for. I've tried Uppers from 16" to 24" and bullet weights from 50gr to 75gr; and there's a lot of potential there.
Suppressors? They don't interest me (too much big, nosy government interference), and if I want to shoot subsonics, I'll be using the .22LR.
For full bore cartridges, maybe an AR-10/Stag 10; I'm still contemplating my first one, and dithering between 6.5CM and .260 Rem.
Greg
For a Pistol Caliber Carbine, I'd rather get the Ruger PC Carbine and be done with it. It is a caliber-specific design, inexpensive, the reviews are great, and rumors suggest possible additional later offerings in 45ACP, and maybe..., maybe a 40cal. Mine is on order and will be sharing 17rd magazines with my Ruger American Pistol 9 Pro.
If you can't find a versatile selection of .223/5.56 ammunition for your AR, I'd look a little harder; either that, or maybe you're asking more from the system than it's really going to be good for. I've tried Uppers from 16" to 24" and bullet weights from 50gr to 75gr; and there's a lot of potential there.
Suppressors? They don't interest me (too much big, nosy government interference), and if I want to shoot subsonics, I'll be using the .22LR.
For full bore cartridges, maybe an AR-10/Stag 10; I'm still contemplating my first one, and dithering between 6.5CM and .260 Rem.
Greg
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