What's the best alternative cartridge for an AR-15?

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Forte S+W

New member
I've been shopping for a complete upper chambered in an alternative cartridge, but there are so many options that even after reading up on each of them I'm still unsure which one to go with, in fact if anything I'm even more unsure than when I started.

Which is your favorite and why?
 
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DubC-Hicks

New member
It completely depends on the role you want it to fill. Hunting or target shooting at possible longer distances? I like 6.5 Grendel or 6mm ARC. Hunting at 200yds and in, or if I'm wanting a good suppressor host? I like 300 blackout. Are you hunting, but restricted to straight wall cartridges? I'd choose 450 Bushmaster.
 
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stagpanther

New member
In terms of proven reliability and a case design that works exceptionally well with AR components--next to the standard 5.56 x 45 I think 6.8 spc is one of the best. Other cartridges might be more accurate and carry more punch to longer range, but the 6.8 spc gets my nod for "if I could only have one" (besides 5.56).
 
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mehavey

New member
Fair Use Summary:
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Are you looking for a the better cartridge for long range hunting for game like mule deer or pronghorn in open country where you might need to take a shot at several hundred yards? The 6.5 Grendel has a flatter trajectory, will drift less in the wind, and carries significantly more energy out past 200 yards.

Are you looking for the perfect cartridge to use in a short barreled rifle (SBR)? Go with the 6.8 SPC. It performs near its full potential with a shorter 16-18 inch barrel and loses minimal velocity with even shorter barrels. This is in contrast to the 6.5 Grendel which requires a 20 inch or longer barrel for best performance.

Are you sensitive to recoil and in need of a serious low recoil cartridge? Both have very light recoil, but the 6.8 SPC has noticeably less than the 6.5 Grendel.

Do you want the round that is best suited for target shooting out past 400 yards or so in a precision rifle? Again, go with the 6.5 Grendel and use a longer 20″ or 24″ barrel. Especially with longer barrel lengths, the cartridge has a longer practical effective range and really stands head and shoulders above the 6.8 SPC for precision long range shooting.
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https://thebiggamehuntingblog.com/6-8-spc-vs-6-5-grendel/
 
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Shadow9mm

New member
Really depends on what you want to do with it. Personally i have chosen to go down the 6mm arc rabbit trail at this point. Still finishing liad development. Did not like factory ammo at all.
 
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stagpanther

New member
One thing you almost never see discussed when the subject of AR "flavors" comes up is over-all reliability of operation (magazine feed, cycling, chambering and extraction). I'm no expert, but I have built dozens of the things and over time I've learned that reliability of operation is one of the most important considerations (if not the most important) and not how sexy the particular cartridge is. My less than 2 cents.;)
 
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Shadow9mm

New member
stagpanther said:
One thing you almost never see discussed when the subject of AR "flavors" comes up is over-all reliability of operation (magazine feed, cycling, chambering and extraction). I'm no expert, but I have built dozens of the things and over time I've learned that reliability of operation is one of the most important considerations (if not the most important) and not how sexy the particular cartridge is. My less than 2 cents.;)
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I have always considered it a given that it has to feed and function reliably or its garbage. But your right, some people may not have taken that into consideration.

The only non standard cartridge i have run in an ar is 6mm arc. So far it has had zero feeding or cycling problems in my Aero precision upper build.
 
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jetinteriorguy

New member
For me it would be 7.62x39. Now let me explain my parameters. First as a hunter where I live I’d never shoot at anything over 200 yds away and seldom would have a shot over 100yds due to living in a heavily wooded area. Second, if shooting in self defense any shots at 100yds+ I’d avoid and just use evasive tactics rather than draw attention to my position, or I’d lie quietly waiting for a closer ambush depending on the situation. At these ranges my current AR47 shoots sub 2MOA which is more than sufficient to do the job.
 
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zukiphile

New member
I've developed in interest in ARs in 22lr. In the last seven years or so, the aftermarket for parts that allow the building of a very accurate 22lr out of an AR upper and lower receiver have blossomed.

You might not consider 22lr the "best" for range or capacity, but it allows shooting 10,000 or 20,000 rounds a year on a modest budget. For a 22lr semi-automatic rifle costing less than $1,000, I don't think I could make a better 22lr.
 
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czgunner

New member
rickyrick said:
I’d also say 6.8, but factory ammunition was had to find for a few months, but now I’m finding it again
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Its interesting you bring that up. I've found it about the same as 300 body odor, both here in WY and WA.

Sent from my Pixel 3 using Tapatalk
 
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Ed4032

New member
These posts explain the popularity of the AR platform. It can be almost any caliber that you want so easily.
 
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taylorce1

New member
What do you want the alternative cartridge for? It's really hard to beat 5.56/.223 in an AR15 platform IMO. The only alternative cartridge I shoot is .300 BO, and all my AR firearms are shot suppressed.

I did have a .277 Wolverine build going at one time to hunt deer with. I wound up giving away the barrel to a buddy, and just put together another 5.56. The reason is the right .277 bullets are/were difficult to find, and I've been been buying 5.56 cheaper than I could buy the components to manufacture .277 Wolverine.

If you're going to hunt with an AR15 then one of the 6mm and up cartridges might be slightly better than the 5.56/223. However, loaded with a bonded or mono metal bullet the 5.56/223 does a decent job on deer sized game and smaller. The 6mm ARC is interesting if you want to try your hand at steel at ranges beyond 600 yards. But, if you're just going to the range and shooting it's hard to beat the economy of 5.55/223.

The issue with alternative AR15 cartridges is the magazine. It limits you on what you can do with the platform. The 6mm ARC is probably the best optimized alternative cartridge for the AR15 as far as range and terminal performance on deer and smaller.

I've hunted deer a few times with the AR15 in 5.56 and .300 BLK, but I much prefer a bolt action or single shot rifle over the AR for hunting deer. I do like my 5.56 for calling coyotes, but my leg with all its plates and screws doesn't like the cold anymore. I also use the AR15 a bit on prairie dogs, but still prefer a bolt action from the bench.
 
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jmr40

New member
For what I do with an AR 223/5.56 is all I need. And I've seriously looked into alternatives. The 6.5 Grendel makes the most sense for what I would use it for. I considered the 350 Legend simply because ammo is everywhere and reasonably priced.

I keep coming back to the fact that I'd never hunt anything bigger than deer with an AR15 and the heavier 75 gr 223 loads will work just as well on deer as anything else on that platform. The 6.5 Grendel is the only cartridge that will fit in an AR15 that I'd even consider on game bigger than deer.

If I felt the need for anything bigger than 223/5.56 I'd move up to the AR10 platform and choose the 308 or similar cartridges.
 
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mehavey

New member
Georgia Hunting Regs (Deer & Bear)
"Modern Rifles and Handguns: Centerfire only,
.22-cal. or larger with expanding bullets. "
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That make a lot of sense for white tail.
(I'm a little surprised for bear)
 
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