Standard AR-15 lowers with different caliber uppers (6.5, 6.8, 300 and such)

[Purdue1991]

Grendel doesn't seem fussy at all to load for does it? Seems to shoot pretty well with a variety of bullets, or at least mine do. My go to hunting loads have been 120 sierra pro-hunters and 120 speer gold dots. This year I'm using 115 Barnes Tac-Tx. I've used the Tac-Tx in 300 blackout and it worked well. Just moving to lead free rounds for hunting.

I load for the Grendel. No issues. I also use the Sierra Pro Hunter in 120 grain and it's dropped everything in it's tracks.

 

[Expat]

I thought this was interesting. If you are worried about a 300 BO getting in your .223 AR... go H&K.

https://www.hkpro.com/threads/hk-416-accidentally-ate-a-300blk.562791/

 

[STFU]

.300 Blackout uses the same bolt as the 5.56, has low recoil, and should do 200 yards if you do your part.
One caveat.
Since they do use the same bolt and magazine, it's easy to get the upper mixed up with the 5.56.
You do NOT want to accidentally load a 5.56 round in a .300 Blackout gun.
Bad things can happen.

Come on, git some...

Seriously. My uppers and mags are labeled clearly:

AR-15 300 AAC Blackout Dust Cover - Premium Laser Engraved I www.customardustcover.com

 

[ws6duramax]

The 6.5 Grendel gets my vote, very versatile round. I bought a BCA side charging upper that was very accurate AFTER the first shot. My first cold bore shot was always about 4" off @ 100yds and I could never get it get figured out, BCA was no help either. I ended up replacing the barrel with a Faxon Gunner series and it's been great ever since.

I used to buy some BCA uppers, but their lack of support pissed me off, so I'll no longer buy anything from them. I've killed pigs, yotes and deer with 6.5 and it has always been clean kills so far.

 

[Squid556]

hopefully this sheds some light on what you're looking for.

This chart shows compatibility


This one shows some ballistics.


I did this write up a while back. Kind of a fun project with some useful info.

6.5 Grendel / 6.8 SPC, 20 Years, Where Are They Now?

Fair warning. Full length Squid spiel, so ya may want some coffee and popcorn . :popcorn::coffee: Without a doubt, when talking AR calibers it seems everyone has their own take on “everything wrong with 5.56”. Doesn’t seem that long ago but around 2003 the 6.8 Remington Special Purpose and 6.5...

www.indianagunowners.com

 

[dak109]

The thing with most ballistic charts I have seen is, they don’t all use the same barrel length. It’s not really apples to apples when one caliber is tested in a 24” test barrel, and another tested in a 16”. As mentioned, the 6.8 shines in 12-16” barrels. The Valkyrie and others need that 20”+ tube to get up to velocity.

 

[Osprey]

Come on, git some...

Seriously. My uppers and mags are labeled clearly:

AR-15 300 AAC Blackout Dust Cover - Premium Laser Engraved I www.customardustcover.com

I wish I thought of doing this. I have so many ARs with different calibers (including 7.62x39) that I forget which is which. Instead, I based it on the scope that I have on it to remind me what ammo to use.

 

[Mgderf]

I wish I thought of doing this. I have so many ARs with different calibers (including 7.62x39) that I forget which is which. Instead, I based it on the scope that I have on it to remind me what ammo to use.

Ok for you, but what happens if you pass unexpectedly, God forbid?
Someone else will not know which scope means what caliber.

 

[loudgroove]

Ok for you, but what happens if you pass unexpectedly, God forbid?
Someone else will not know which scope means what caliber.

Isn't calibers stamped on the barrels?

 

[Mgderf]

Isn't calibers stamped on the barrels?

Yes, but some of my stamping are covered by the hanfguard and hard to find/see.

Better safe than sorry.

 

[loudgroove]

Yes, but some of my stamping are covered by the hanfguard and hard to find/see.

Better safe than sorry.

Ahhh, didn't think about that.

 

[edwea]

This modularity is one of the major caveats to the ar platform. Don't get me wrong, I love ar's. It's one of my favorite platforms. But they can be chambered in so many different cartridges with little or no visible distinction without removing handguards. It really is a recipe for disaster for anyone without knowledge of that specific gun or guns in general. It has me thinking about having the chambering engraved in a visible location on the upper receiver.

 

[JoeSig]

Good afternoon, looking for knowledge!!! I am very familiar with standard AR in 223/556. Looking for youth deer hunting upper here in Indiana. Public land not an issue, private only so I am not forced with straight wall. I just have extremely limited knowledge in the 6.5 Grendel, 6.8 SPC and 300 blackout. Anyway, I have standard AR lowers so it needs to fit. What calibers match to standard bolts? I see the term 6.8 SPC and 6.8 SPC II, and do not see an ammo difference with that. I am leaning away from 350, 450 and 458 for less recoil and true rifle cartridges advantages. Will standard uppers in the 6.6, 6.8 or 300 be capable of 2 inch groups at 100 yds?. Any other valuable info would be appreciated.

I have been running 300blk (7.62x35) as my primary AR for quite some time now. It should be noted I load my own ammo for it. Ammo is quite expensive, especially sub sonic loads. 200 yards is quite easy with anything 168 grain and lighter.

My 110 VMAX loads are comparable to 7.62x39 - they are my SHTF loads as they are good out to 500-600. Subs are really only effective out to 150-200. Downsides to 300blk are that it is not capable of penetrating common body armor and you cannot (safely) get an AP round moving fast enough to penetrate steel plates, at least in an AR platform. It will take down most midwestern game just fine with the right round. A quick google search will tell you what ammo to buy for hunting, but generally 110-125 grain works best. 220 grain subs are fun to use for pest control if you have a suppressor.

All you have to do is buy a new barrel for it to work! While it isn't necessary, I would suggest purchasing dedicated 300blk Magpul mags. They tend to feed much better and leave less mess on your feed ramps. They are $15 most places.

*Edit: Forgot to mention that you will need a new gas tube as 300blk uses a pistol length system to get the AR bolt to cycle. You may have to mess with different buffer weights. If you run a suppressor, I would recommend getting an adjustable gas block that bleeds off excessive gas, such as the Superlative arms gas block.

 

[STFU]

If you run a suppressor, I would recommend getting an adjustable gas block that bleeds off excessive gas, such as the Superlative arms gas block.

Or buy a "flow-through" design that does not cause this issue.
EG: Huxwrx (AKA: OSS) or similar.

 

[JoeSig]

Or buy a "flow-through" design that does not cause this issue.
EG: Huxwrx (AKA: OSS) or similar.

Right, the Huxwrx Ventum 762 is a nice can. I run a CGS Hyperion because it is just stupid quiet. I'd still run the adjustable gas block for fine tuning though because I just can't leave anything alone lol

 

[Osprey]

Ok for you, but what happens if you pass unexpectedly, God forbid?
Someone else will not know which scope means what caliber.

Hmm. I guess it didn't dawn on me since my family are anti-gun people. They would probably trash it somewhere or sell/donate it and I'm sure the next owner(s) would know or perhaps a gunsmith would. Fortunately, I sold all my .223/5.56 so no one can make a mistake with my 300 and the others, the bolts may look bigger/different.