Silly question: which 30 cal for my next AR? 300BLK, 308 or 7.62x39?

After limiting myself to 223, 308 and 6.5CM in my rifles for many years, I'm at a crossroads for my next rifle. I already have .223 in 11.5", 14.5" and 16" ARs as well as a 308 LMT with 18" barrel and a 6.5CM 24" bolt gun. I'm trying to decide between these three calibers for no particular reason:

1. 9" 300BLK
2. 11.5" 7.62x39
3. 13" 308

The 300BLK, of course, brings subsonics to the table. However, although I have a 30 cal suppressor, my local range(s) always have other shooters that are unsuppressed. The 7.62x39 is cheapest to shoot of the three and 308 is the only one of the three that I already have ammo for. The idea of a 308 SBR is also tempting for some strange reason. Any of these three could be used for home defense, hog hunting, range days, etc. I don't have a specific use-case for them, but just thought I'd ask for some opinions and possibly have a discussion.

I've noticed prices on 762x39 going up. It's not the budget panacea it used to be.

I'm a huge fan of 300blk in really short barrels.

The SCAR 17 SBR is pretty sick though, especially with the recent updates.


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I did some searching online and it looks like 9” 300BLK will get about 2100-2200 fps with commercial 110gr loads. While a 13” .308 can get about 2400 fps with most commercial 168gr, 175gr and M80. My 18” .308 gets only 200-250 fps more. I don’t reload, so no custom hand loads for me.

Maybe I’m looking at it the wrong way? 300BLK strength seems to be subsonic close-range and 13” 308 brings mid-range punch. Which would be more satisfying if I already have 11.5” .223 and 18” .308?

I’ve never been an AK guy, so anything 7.62x39 will be a novelty item. It may not be in the running for long.

Maybe I'm just getting older, but unless the 308 is a heavy gun, it's not fun to shoot at all. 300 is too niche for me, and 762X39 is home in the AK. So I vote for 5.56mm!!! :cool:

And I thought maybe I was getting older because my LMT with 18” stainless barrel, 3-15x scope, bipod and suppressor is getting a bit heavy for me!

If you don't reload, subsonic Blackout in commercial loads is hit or miss whether or not it stays subsonic. It really shines when you can roll your own and create a load tailored to your rifle. This is just personal preference (everything is) but instead of a shorty 308, I would do a short 6.5 Grendel. You didn't say whether you hunt or not, but a 12.5" barrelled Grendel is a treat to carry and still packs plenty of wallup. You can use your 30 cal suppressor on it too. I will grant you that ammo is harder to find for it than a 308 but being the smaller AR15 frame a comparable sized rifle in Grendel is going to be lighter than a 308.

308 would be my favorite


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.308, but I might be biased. I refer to .308 Win as "God's cartridge" and have been told I hold the cartridge in such high regard, I'm not just a fan, I'm a member of a cult. Fair enough, but .308 still gets my vote.

9in 300 Blackout gets my vote. second pick with be the 308, but seems like 13 inches would not be much fun to shoot.

Might just be me, but I see 300BLK or x39 as being minor variations of a 5 56 gun while .308 is a more significant step. Sorta like engine options in an F150 vs making the jump to a 3/4 ton.

You gotta decide for yourself how far outside of your current box you want to go. What is the intended use that is driving you to 30 cal? Is it is just to have something different? What do you expect the gun to do better than a 5.56? You seem not to have defined answers to these questions.

In my case I went from multiple 5 56 ARs, added .308, then 9mm and .22lr.. I have yet to add 300BLK and I have AKs in the x39 flavors but not ARs. I also have multiple other guns in a spectrum of loadings. My ammo logistics are way more complicated than yours.

Though I have not followed your path of stocking limited cartridge types I do find merit to that philosophy. Were I in your shoes I would consider adding cartridges to the mix only if you feel the need to fill a specific role. I seriously consider myself to have an overly complicated "logistical chain". I stock 5 pistol calibers, 7 rifle calibers, plus .22lr and 12 Gauge. Your way is better.