Best caliber for AR-15 lower

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sigshepardo

New member
I want to buy another upper for my stag arms lower (5.56). I want the best performing long range caliber that I can put on the small lower. I understand that cartridges like the 6.5 creedmoor are going to be better performing. But I want to see what is going to give me the best groups at long range (700 yds) out of the small AR lower. What calibers do you recommend? Thanks
 
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Chinny33

New member
the 2nd most popular AR-15 caliber is the 6.8 SPC. the 300 blackout is popular-ish, but is still a baby when it comes to cartridges. The 6.8SPC has been around since ~2002? I have an Ambush 6.8 for hunting. Uses specialized magazines. Its a pig killer for sure. Uncommon around local gun shops. Great choices online for ammo. Has a cult-like following. Personally its a great sub-300yd round. I wish it could reach out and touch more. The bullets fail in B.C.

The 6.5 Grendel is a fantastic round also but is highly specialized as a short action high velocity cartridge. Again, very new to the scene. 2012 SAAMI accepted it. Standardizing a round has the potential to make it a great seller. With the extra space for powder, the chamber supports higher pressures, which can lead to throat erosion quicker than a 556/223. Expensive, uncommon round. Utilizes specialized magazines. SUPER high B.C. bullets. I would choose this as my next option personally.


.458 SOCOM. Its my midwest whitetail hunting round. Many states that only allow shotgun slugs only, also allow the .458 SOCOM. Im pushing the same bullets a 45/70 uses to CLOSE the same FPS. Uses standard magazines. Expensive, almost impossible to find off the shelf. The brass alone cost me $0.80/rd. Super easy to reload.


very important to note that I reload. If you dont reload, I feel sorry for you spending money buying ammo off the shelf and throwing the brass away.
 
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globemaster3

New member
First, you need to realize the limitations of your AR-15 lower. You are not going to be able to switch to an upper made for the .308-based cartridges or others of equivalent length. The dimensions of the magwell prevent this. Since you mentioned 6.5 Creedmore, I thought it important to mention.

Now, for your situation, there are a lot if cartridges to consider, and a quick search on the forum will reveal a lot of threads where they are listed. 6.8 SPC and 6.5 Grendel are 2 good choices, but you can go to WSSM chambering if you so desire.

In the end, you need to come to terms with exactly what you want this new upper to do and then look at the cartridges that can realistically perform, taking into consideration ammo support and reloading possibilities.
 
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CTS

New member
I agree with globemaster3. First decide what your purpose for this upper will be. In my opinion, if your intent is hunting, I would go with a 6.8SPC. If it is long range target shooting, I would go with the 6.5Grendel. Just my two cents worth.
 
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Xfire68

New member
Expensive, uncommon round. Utilizes specialized magazines.
Click to expand...

The Grendel does not use specialized magazines. They use standard 5.56 mags with a reduced capacity of 26 rounds. The Grendel does however use a different bolt.

Although factory ammo is expensive and uncommon now I only see this cartage becoming more and more popular over time. For a reloader this is a great option for a AR platform hunting rig. Many many .264 projectiles to choose from.

Right before just about every AR part in the country sold out I was looking to buy a upper in 6.5 Grendel. Now I have to wait till the prices adjust or find a used one at a reasonable price.
 
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madcratebuilder

New member
The most accurate AR15 platform caliber is the 6.5Grendel and has been for years. A lot of different factory ammo available, Hornady and Wolf both have several loads. With the new pricing of 5.56 nato, Grendel may be cheaper.:eek:

The Grendel requires a proprietary bolt, barrel and magazine with the correct follower.

Your 700 yd goal is just the starting range for the Grendel.
 
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Dr Big Bird PhD

New member
Why do you need to shoot out to 700 yards?

If that distance is a must for the AR platform (I'd consider a different one altogether), then the 6.5 grendel is the only one that can do it reliably.

However, the 6.8 SPC is the most common AR hunting cartridge. You can find it at most ranges and almost all respected LGSs. And it DOES perform very well past 300yds. Maybe not past 500, but definitely 3.
 
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sigshepardo

New member
Update

Just an update for everyone. Trying to clarify some points. I want to be able to hit the long range gong at my local range (750 yds) accurately. But I don't want to buy a long action AR lower. I'm asking for what your opinions are on the most accurate short action calibers for my AR at 700 yards. Thanks
 
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CTS

New member
6.5 Grendel would be my bet. I am a 6.8 owner but I came real close to building the 6.5G. I got to realizing that I didn't need to shoot at anything over 300yards (rarely even 200) so I went with the 6.8 instead.
 
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