What's the best alternative to 5.56 for an AR-15?

Well Armed · Nov 9, 2023

Forte Smitten Wesson said:
Alright, but that begs the question whether the cost savings are offset by the additional cost of 7.62x39 AR Magazines?

I imagine that after purchasing a few magazines the cost savings in ammunition aren't going to make up for the additional cost of magazines.

Here's my unbias and objective opinion:

Full disclosure: Biden and Democrats banned all the inexpensive x39 coming in. x39 is cheaper probably for a few more years, but I don't know what the future holds. Cost might stay the same or not.

My suggestion? Buy the best and least expensive x39 or 300 blk upper you can finded now. Pick up the other later. AR15s aren't that expensive especially when all you're buying are uppers. You can get 2 uppers for around the price of one striker-fired polymer wonder.

7.62x39 is the superior round when it comes to penetration and CQB. It's tried, true, vetted, has been used in wars and conflicts, and is way more popular worldwide.

300blk has pluses over x39 in an AR15 platform only which are it uses the same mag and bolt as an AR15. Unlike the x39, the x39/300blk bolt is better suited for the platform.

I perfer x39 in an AR platform because ammo is currently cheaper, I already own over a dozen AKs, I have a few thousand x39 rounds on hand, and because x39 is a superior round.... That said, if the cost of x39 ammo goes above or equal to 300blk, I'll probably switch. If both the cost per round of both x39 and 300blk soars above 2.23 and 5.56, my main defensive rifle will probably be a 10.5" 5.56. If you aren't going to use a short barrel aka using a sub 10.5" barrel and/or you aren't interested in using subsonic ammo and a suppressor, I don't see the point in not just sticking with a regular M&P Sport. .223/5.56 is barrel length and velocity dependent and 300blk and x39 is not which is the only reason why I went with a different caliber for a short barrel AR.

As far as 308win is concerned. I own G3 variants built by PTR and AKs Veprs in .308, and I'm assembling an AR10. 16" in 308. My issues with using 308 is the size, weight, and cost of the ammo and rifles are much more compared the x39, 300blk, .223/5.56. I won't be mag dumbing or shooting several full rounds of mags of 308 like I would other less expensive AR rounds.

bulletslap · Nov 9, 2023

I have 5.56, 300blk, and 7.62x39 uppers. Each of them have their place.

I believe the 6x45 would be a better Utility cartridge than them. I might order a barrel and dies when I get caught up on my projects.

WR Moore · Nov 9, 2023

I don't know anyone who's tried to build an AR for 7 mm TCU (.223 necked up to 7mm), but the little cartridge has always interested me. I was thinking of picking up an H&R handi rifle and making a barrel for it, but then they went out of business.

If you want something you can buy factory ammo for, the .350 Legend would seem to be a good choice.

In re: vamint calibers. I once knew a gunsmith in NW PA who used to shoot groundhogs with a .458.

noonster · Nov 10, 2023

AR15 platform

“Regular” big game 6.5 Grendel is hard to beat. Build a stash of ammo or reload - the 6.5 is used to good effect all over the place. If you want to go with bigger bullets, it becomes a single shot (one-at-a-time) and they can be thumpers. Big snarly game - check out the 50 Beowolf. 50 cal on an AR15 can be done. Look up cartridge development for both - Alexander Arms were pioneers in the development of them. The Beowolf is not a long range prospect.

rwsmith · Nov 10, 2023

I figured.....

...that 'best' would be the 6.5 Grendel. You can use it to hunt in SC and it has good long range capability. However, since I don't hunt and seldom shoot past 100 yards, either the .300 Blackout or the 7.62 x 39 would be good. When they get rid of stupid laws that say suppresssors are a danger to society, I would prefer the Blackout as I already have an 7.62 x 39 SKS that I really like.

hardluk1 · Nov 10, 2023

STORMINORMAN said:
Uh, the OP said "... for an AR-15?"...

Cheers!

Do you really think most of these mutts pay attention to an opening tread , nope .

The OP did say ar15 that most seem to not pay attention too and just run off on there personal preference . Still for the OP to ask what cartridge to use on a AR15 he has to be a newbie or he would have never ask .

Well Armed · Nov 10, 2023

hardluk1 said:
Do you really think most of these mutts pay attention to an opening thread , nope .

The OP did say ar15 that most seem to not pay attention too and just run off on there personal preference . Still for the OP to ask what cartridge to use on a AR15 he has to be a newbie or he would have never ask .

The OP already owns an AR15, but he wants to know which is the best alternative caliber to get another upper in.

gdogs · Nov 10, 2023

350 Legend is what you are looking for. Ammo is plentiful and affordable, from cheap pinking loads to hard hitting hunting rounds. I really can't believe I'm the first to mention it in this thread, as it is the most obvious choice. 7.62x39 is limited to decent bullet selection, 300 BO is for shooting pigs quietly in the dark (the only thing it does better than the 350), 6.8 is a decent round for mid sized game out to 250yds. my 2 cents.

walnutred · Nov 10, 2023

Looking at alternative AR chamberings I'm thinking that the 300 Black Out and 350 Legend is just dancing around the 8mm Kurtz.

smoothshooter · Nov 10, 2023

Ever fire a high-intensity cartridge inside a house or smaller confined space with no hearing protection? Try it some time.
Get a handgun in .38, .45, or even .22LR for in the house, and a .30-30 or some bolt gun for outside.
The AR-15 in 5.56 has some usefulness for varmints and some big game with well-placed shots. Works good on humans. Good range toy too.
I would not pick an AR-15 as an all-around rifle.

rockquarry · Nov 10, 2023

There's been little or no mention here regarding velocity loss with extremely short barrels such as 16". It can be quite significant depending on the cartridge. With the .223, I've seen around 300 fps difference between a 16" AR barrel and a 24" barrel on a bolt-action rifle. That's a lot. All the various short make-it-fit-the-AR chamberings suffer accordingly with regard to velocity loss.

If working within the confines of the AR setup along with the short-barrel fad, these are real handicaps that should be considered and addressed, but usually aren't. It appears that being able to cheaply swap out tops and bottoms is far more important than cartridge performance. That's not a critical remark; depending on needs and wants, the AR setup may work fine for many. Limitations and disadvantages may be of little concern to the users.

WR Moore · Nov 10, 2023

Forte Smitten Wesson said:
Oops! Sorry, it hadn't occurred to me to mention it, but as far as Hunting goes, the biggest animal I'm likely to encounter in my state is a Black Bear, and obviously I wouldn't be hunting those.

So yeah, if I were to actually hunt anything it would be Deer. Granted, I don't actually plan on hunting, I'd just like to have a sort of all-purpose round that could be used effectively for hunting.

OK, given the conditions presented here, there might be an easier answer that you might not have considered: the ammuntion. Specifically, the bullet.

If you search the ammo companies websites, you'll see certain products specificially designed for use on deer and other medium came. Loooong ago, Winchester developed a 64 gr Power Point bullet for this purpose. They've since created other products. As have Federal and Hornady including bonded core bullets, dual core bullets and at least one monolithic copper bullet. I've read rave reviews by experienced guys about the effectiveness of various monolithic bullets on medium game in .223/5/56 mm.

Depending upon intended usage, you might also visit hornadyle.com. The ballistic gel comparisons aren't available without a secret handshake, but they can be interesting in comparing A to B. I long ago found that Hornady uses a 75 gr HPBT in some of their LE ammo. I have to wonder if they actually produce a separate bullet for that usage or just the regular HPBT. Have asked Hornady, in the mean time I need to save up some milk jugs.

brendonjames65 · Nov 10, 2023

So for big game, assuming deer, hogs, black bear, personally I like the AR10 platform in 308 for this purpose. But sticking to the cartridges you listed:

The 6.5 Grendel and 6.8 SPC offer the best overall ballistics especially at longer ranges. However, ammo may not be as common. Require a barrel, bolt and IMO a magazine change or tweaking for reliability.

The 450 Bushmaster, 458 SOCOM, 50 Beowulf are hammers for sure but IMO more short range propositions but can certainly handle big game at the shorter ranges. Barrel, bolt and mag changes. I believe a standard AR-15 metal works for the 458 Bushmaster to hold 10 rds but not the Magpul plastic ones. All require barrel, bolt and either specific mags or modified mags. Also ammo may not be as popular.

Now you’re down to the 300 Blackout and 7.62x39. Both similar ballistically, slight edge to the 7.62x39, but not meaningful IMO, both 30-30 level power but with pointed bullets for better ballistics unless comparing 30-30 Lever evolution ammo. The 7.62x39 requires a new BCG or a new upper, barrel and mags specific for the round. Ammo is certainly plentiful and cheap for this round.

The 300 Blackout is the hands down easiest to convert to, just a barrel change and nothing else. Same BCG, same mags, every other part is the same as the 5.56/223 except the barrel. The only caveat for the 300 Blackout is if you’re going to run heavy subsonic rounds ideal for a suppressed AR the gas system must be set up for that. I run normal velocity rounds from my AR15 300 Blackout, 110 and 125 grain. I think 300 AAC/Blackout ammo had come down in price and much more available these days.

So my recommendation is the 300 blackout! However, really I think an AR-10 308 is the best solution!

biku324 · Nov 10, 2023

My next rifle will be a Colt CR 6762 in 7.62x39. It will do anything I'd like, including with SPs for deer.

We've been training Somali police with AK-47 variants and I've come to an appreciation of the round. Don't care for the AK rifle (I've fired M16/AR-15/M4 for most of my adulthood), but now really like the 7.62.

noonster · Nov 10, 2023

Upper

I’d think that easiest would be an upper in whichever caliber. Nobody wants to monkey around with barrel - etc - change-outs. At least, I don’t.there are a number of good choices for upper, as I mentioned further up.

ladder13 · Nov 10, 2023

Never seen anyone hunt with an AR?

I have not only seen, I use one in the big woods of NC.

Many of the gents I hunt with do likewise, with various calibers. Never saw one in 7.62x39 though.

Mine= 300 BLK, SBR, and this year, suppressed.

Previously

Hair Trigger · Nov 10, 2023

CH4 said:
I like the 300 BO and 6.5 Grendel. Don't know why, just do.

Same here, and those are the calibers that my only two AR's are in. I built my Blackout as a CQB carbine, would have gone SBR but didn't feel like giving BATFE the money for the "right" to have one. Around here, a lot of hog hunters like the cartridge for its bullet choices, light and fast or heavy and subsonic. I built my Grendel specifically as a long range rifle and it hasn't disappointed. It's basically a short action Creedmoor.

As to the poll question, I think the best cartridge (other than .223/5.56) depends on what you want to do with the gun. .50 Beowulf might be darn good for short range wall penetration with enough left over to kill what's beyond, but not as an overwatch/sniper platform. Then there are those calibers that are so close to each other you could argue their merits all day without resolution.

bulletslap · Nov 10, 2023

The 7.62x39 case head is close to the limit for the standard AR15/M16 bolt head. So far mine hasn’t failed, but I did buy a spare.

A year or so back I saw a 7.62x39 built on the AR10 “platform” and I was intrigued by it. As far as I know nothing has be released commercially. But I think it would make an interesting rifle.

gdogs · Nov 10, 2023

Here's my 350 Legend, 13" barrel.

Was a pistol, now a registered SBR. Hands down my favorite rifle for the woods. If your shooting within 150 yards, there is no better option in my opinion. Velocity loss for the 350 with shorter barrels is minimal and therefore makes a great pistol/sbr option.
Great video of barrel length testing, cutting off an inch at a time.
[ame]https://www.youtube.com/watch?v=7u4Oc32QQ_M[/ame]

Echo40 · Nov 10, 2023

I'm pleasantly surprised to see that .300 Blackout is leading the polls since that was one of the two cartridges that sounded best on paper to me prior to me posting this thread.

Amusingly enough, the other other one (.458 SOCOM) is effectively tied with .50 Beowulf as the least voted-for cartridge since I'm one of the three people who voted for it, mostly so that I could see the poll results without having to click "see results" every time.

What's the best alternative to 5.56 for an AR-15?

What's the best alternative chambering for a general purpose AR-15?

.300 Blackout

6.5 Grendel

6.8 SPC

7.62x39

.450 Bushmaster

.458 SOCOM

.50 Beowulf

Other (Specify in post)

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