AR 15s in calibers other than 5.56 NATO

[Balrog]

I would like to hear pros and cons of various calibers of AR 15s, larger than 5.56. I would not plan to suppress it. What caliber would be best in terminals of terms of terminal ballistics, reliability, and ammo availability?

Specifically talking about AR15 pattern rifles, not derivatives like the AR10 or SFAR.

I would want it to be able to use standard AR magazines also.

 

[wesmonster]

standard mags? Then that's just .300bo. Which is a fun caliber, I don't own a can but enjoy shooting subs & supers from both a 16" and an 8" upper. Same mags & bolt so probably the easiest caliber to jump into.
I shoot 5.56, .300bo, 7.62x39, 5.45x39 & 6.5 Grendel out of ARs. The only caliber that works out of 5.56 mags is 5.45x39 and that's only from certain GI straight 20s with tilt followers. Everything else has their own mags.

I do have a few Unimags which are advertised as feeding most variants. They work fine in all my calibers but I already had plenty of dedicated mags, and Unimag is no more. Their msrp was high til they were discontinued, that's when I grabbed a few.

I've tried every combination of the above calibers in different caliber mags and at best they'd work 75% of the time in the 'wrong' mag.
I also shoot a lot of 7.62x39 out of other platforms so it made sense for me. Already got a pile of it.

6.5 Grendel is the best performer of the bunch, but all the cheap steel case is gone, but if you reload it's a fun caliber.

No experience with .458 socom or .50 Beowulf but I think those can be shot from 5.56 mags.

 

[N555]

Sound like you want 5.56.
Anything that fits in the standard AR15 pattern mag that isn't 223/5.56 is 2x to 5x the price for ammo.
The only thing that isn't always 2x the price or more is going to be 300blk, it's 30cal but rounds are loaded with less powder than 5.56 rounds so terminal performance is maybe better than 5.56 because it fires bigger bullets but ballisticly it sucks.

 

[LimaCharlie]

Alexander Arms AR-15 in 50 Beowulf.


Double-stack magazines become single-stack magazines.

 

[mcb]

300 AAC Blackout is a good choice. If you're certain you never going to own a suppressor then you could step up to a 300 Ham'r. It sacrifice the subsonic capabilities to optimize it super sonic ability. 300 BO works with standard magazine in most cases. 300 Ham'r usually wants 300 Blackout magazines. 300 Blackout is widely available, 300 Ham'r less so.

350 legend is becoming very popular for a very new cartridge. It does require 350 Legend specific magazines but is widely available.

450 Bushmaster is a good candidate. It will feed from standard straight 20rd AR magazines. It is also widely available

There are a bunch of 22 to 30 caliber cartridge that will run in the AR platform but most of them require non-standard magazines. That said the magazine issue is pretty tractable.

 

[Space Ghost]

Yeah...
I got nothing.


Go 5.56.

 

[mcb]

Try this, a nice list of AR compatible cartridges. There is something on the list for nearly any application you might want to apply an AR to. There are cartridges from .17 cal to .50 cal and every remotely common caliber between the two.

https://en.wikipedia.org/wiki/List_of_AR_platform_cartridges

 

[CapnMac]

I'll endorse the above.

Just wait until the 22arc spreads around a bit--then we will get all kinds of arguments about whether 223 is "better than" a 22-250 equivalent. That latter will be heavily influenced by some of the bullet weights already being touted for the 22arc.

 

[InTheSwamp]

I would focus on the application, then select caliber - so many to choose from.
5.56/Wylde are the best all-around chambers, IMO, but for hunting I'd go 6mm ARC or just wait for the 22 ARC. There are other wildcats that can suit your needs.
The big bores are fun to shoot and easy to handload, but your shoulder will take a toll.

 

[CoalCrackerAl]

I enjoy my .556 and 223 Wylde and 7.62x39 AR'S.

 

[marksman13]

Just stick to 5.56 or drop your commitment to standard mags.

 

[bearcreek]

I would not plan to suppress it. What caliber would be best in terminals of terms of terminal ballistics, reliability, and ammo availability?
I would want it to be able to use standard AR magazines also.

5.56 with something other than ball ammo. I have yet to hear/read a convincing argument to go with something else.

 

[LoonWulf]

375 socom, 458 socom, 50 Beowulf.

I haven't had the 375.

The other two basically launch bullets of the same weights at the same speeds, primary limitation is the strength of the AR-15 smaller bolt head.

Pros.
300 grain bullets in nearly 2,000 feet per second trump 60gr bullets at 3000 feet per second at short range.

Cons.
Significantly less ammo capacity, since as noted the standard magazine becomes a single stack.

Noticeable increase in recoil.

Stupendously steeper trajectory.

Unless you're shooting something that the standard 556 can't stop, You're giving up a lot of everything else to get the bigger bullet.

 

[KKJ13]

I have two 50 Beowulfs, they can both be finicky unless loaded hot. They are the most fun of the bunch but you must reload if you want to shoot it a lot. Also have some 300blk’s that are fun with the suppressor. The 9mm ones get shot the most though, by far the cheapest to feed but definitely not standard mags. I really don’t shoot any of my 223/556 ar’s as they are pretty meh, and I have a variety of them too in that cal.

 

[Cfish]

Don’t forget the .277 Wolverine

 

[Riomouse911]

Adding 7.62x39 to my quiver of 5.56 AR’s only required a new upper, BCG and some C-Products magazines.

The 7.62 AR has been super reliable and fun to shoot, hitting my steel plates with more oomph than my 5.56 guns do.

Stay safe.

 

[P Flados]

I recommend moving past the magazine issue. Just get a couple specific to your application and pick the best cartridge for your need.

Terminal ballistics for the 350 Legend is a strongpoint (if you are not talking longish shots) given the good variety in available hunting ammo. Ammo availability and cost is better than most other choices. Recoil is more reasonable than the 45 cal choices.

6.5 Grendel is about as good as it gets for something between 22 and 30 cal. Actual performance is hard to beat in the AR-15. Ammo situation is more tolerable than the really oddball choices.

300 BO is popular but actual performance is not really that good. 300 Ham'r tweaks just a little more performance but not enough such that I would recommend it.

 

[cfullgraf]

I have built AR-15's in 300 Blackout, 6.8 SPC, 6.5 Grendel and 6x45. They all work fine and will work fine for their intended capabilities.

For around my hobby horse farm, I prefer 300 Blackout. Good performance out to 100 plus yards but limits collateral damage beyond that range.

The other cartridges have their advantages and disadvantages.

My main prairie dog rifle is a 26" heavy barrel, 204 Ruger AR-15.

 

[rb288]

I have ARs in several calibers.
300blk, 6.5 grendel, and 450bm.
300blk supers run fine on 556 mags, heavy subs not so much, but do run on dedicated 300blk mags like those from Lancer.
6.5 grendel run fine on 556 mags.
450bm will work on 556 mags, but are not always reliable. It needs either single stack followers or dedicated 460bm mags.
When used with the proper mags, these variants run great and add to the versatility of the platform.

 

[edwardware]

7.62x40WT (Wilson Tactical), and it's slightly younger sibling, .300HAM'R. Both need a barrel, and magazines with the shoulder rib shaved, but otherwise run through standard parts and easily formed brass.

Either puts .300BO in the shade for any unsuppressed use.

 

[KKJ13]

One benefit of having dedicated mags for each caliber is no kabooms from inserting the wrong one at the wrong time. Sounds like some kind of inuendo but is a real possibility. Not so much from an experienced person but someone else not so familiar.

 

[alfsauve]

I’m a 458SOCOM fan. Won’t chamber in 5.56 barrels. Can use same magazines. Great <100 yard thumper.

 

[mcb]

My current collection of ARs: 22LR, 5.56x45mm, 300 AAC Blackout, 30 Remington AR, 450 Bushmaster.


Tough firmly in my cheek. You could go to the opposite extreme and buy an old 30 Remington AR upper. Nearly everything in the upper is proprietary. The upper itself, the bolt, the barrel, barrel extension, barrel nut, handguard, and the magazine is down right funky.


30 Remington AR 4-rd Factory (only feeds from the left side), 450 Bushmaster 5-rd factory, NHMTG 5,56x45mm straight 20rd.


30 Remington AR (its a modified DPMS LR-308 bolt lug pattern with a body that allows use in a standard AR-15 bolt carrier, 450 Bushmaster bolt, Standard 5.56 bolt. (yes they are all dirty)

30 Remington AR brings close, but not quiet, 308 Win performance to the AR-15 platform when using medium to light 30 caliber bullets.

Killed several armadillos and a nice buck last year with it.



Any yes this is a completely unrealistic post for this thread, 30 Remington AR uppers and rifles were only made in low numbers for 2-3 years over a decade ago and ammo is getting hard to find. With the demise of Remington we will probably never see new factory guns, parts or ammo again. There is a small group that is trying to revive it but they are going slow.

-rambling

 

[Necessary_Nutrient]

If you reload, 6.8 SPC is a good choice, very reliable with decent magazine choices and good component availability. Factory offerings in 6.5 Grendel or 6.8 SPC are both decent and offer a trajectory advantage over 7.62X39. You get a good 40%+ bump in energy going with 6.8 over .223

Daniel Defense, PSA, Rock River arms offer good 6.8 SPC platforms

 

[illinoisburt]

A lot depends on usage. Lately I've been using my ARs for hunting hogs at night. Generally it's under 200 yards for which the platform has been working well with 7.62x39 and duramags. If steel 6.5 Grendel was coming in cheap I would buy an upper today as it has a bit better trajectory with similar weight and speed bullets. But you may be doing something very different for which these choices won't fit well.