The 8" to 12" Barrel .30 Cal Carbine

[Sanch]

Note: This is probably an idea that isn't worthy of this forum and is more "other" forum nonsense. I do pose the question in earnest and am think there's value in discussing it even if it's silly for a civilian LARPer like me to worry about it.

About 15 to 20 years ago, I got enamored with the idea of the Krinkov in 7.62x39. A compact short-barrel rifle with an 8" to 12" barrel that pushed a 7.62 bullet of around 125 grains very fast. At the time, alternatives were 5.56 which had shitty ballistics in short barrels using ammo at the time, and were difficult to make run reliably in an AR platform. But an AK is an AK even in a short barrel.

I'm just a civilian LARPer but my idea was a close quarter fighting carbine that would do good around vehicles and intermediate barrier penetration capabilities. Small, loud, aggressive. But unlike 5.56, you wouldn't be wasting as much unburnt powder through the shorter barrels. I shelved the idea because I had an SBR AR lower and didn't want to deal with NFA for an AK as well. And my 11.5" 5.56 SBR with modern ammo is pretty good.

But now I started looking at 300BLK more seriously, which seems like ballistically similar to 7.62x39 except it can be run in an AR platform without the same compromises, and using the same 5.56 mags. I know dedicated 300BLK mags exist, but it's nice being able to interchange mags, if you need to. Looking through the massive Sig MCX Rattler thread got my spending-money juices flowing.

And also now we have forearm braced pistol AKs so I could get an 8" to 12" AK in 7.62 x 39 without dealing with the NFA. Or I could get an 8" barrel 300BLK to put on my SBR lower.

So I'm wondering a few things.

1. Is my original idea of having an 8" to 12" carbine in 300BLK or 762x39 have any validity? Seems like to make it worthwhile, you need to drop down to 8" because if you're willing to run a 12" barrel, the newest ammo in 556 probably with 62gr bonded probably does all of the things I originally wanted the shortie .30 cal carbine to do. It's just that 5.56 is still kind of poopy in an 8" barrel from cycling and ballistic effectiveness.

2. It seems like if you're a professional gun fighter or even a LARPer, then 4" of OAL shouldn't matter much. So if 62gr bonded 556 is really good at car penetration and intermediate barriers, then maybe running an 11.5" SBR in 5.56 is equal enough to an 8" in 300BLK / 762x39?

3. Am I right that out of an 8" to 12" barrel, comparing 762x39 to 300BLK supersonic would be about the same as each other? How about unburnt powder, am I right that it doesn't waste as much powder in a shorter barrel compared to 556?

4. For the civilian LARPer with the budget to afford it, does it make sense to compliment an 11.5" 5.56 gun with an 8" 762x39/300BLK gun? Or is it just kind of silly?

For the purposes of this discussion, I'm disregarding the MCX Rattler with a 5.5" 300BLK barrel because the purpose of that gun isn't "we're doing CQB around cars" but the purpose is "we need a small compact effective gun that can hide in the smallest possible package, 556 doesnt work out of tiny barrels, so here we are with 5.5" 300BLK". I don't think anyone is intentionally choosing to start a fight with a 5.5" barrel Rattler. If they had a choice, they'd probably get an 11.5" 5.56 SBR.

In other words, if you were going into a fight, and you weren't trying to conceal the gun in a small bag (in which case the 5.5" Rattler would win, so there's no need to discuss), is there a scenario where you'd choose an 8" to 12" barreled 762x39 / 300BLK versus an 11.5" 556 SBR?

[Wondering Beard]

I think the following video might give you a different approach to your question:



https://www.youtube.com/watch?v=kVLL6bCXIU4

[Tensaw]

With apologies to Wondering Beard (having not watched the video), I will say that I *really* enjoy shooting my 10.5” 300Blk pistol. (That sports a Vltor A5 receiver extension which may contribute to the feel of the gun, but whatever. It makes me smile. And this is all supers - no subs/can at this point.) I like everything about it except having to shell out for the ammo. So, yeah, given a choice between it and an 11.5” 5.56, I would not hesitate to grab the 10.5” 300 for a fight.

Someone with real knowledge will be along shortly to address your specific questions and perhaps we will both learn something, but for now, here’s my take.
1. The 8” - 12” 300Blk is quite valid. There is a reason why they are so popular.
2. I can’t answer that.
3. For the 300Blk, yes, an 8” - 12” barrel makes very efficient use of the powder. IIRC, the 300Blk was optimized for a 10” or 10.5” barrel.
4. If you have the budget to afford it, the answer is always yes, get both.

For me, for serious purposes, the 300Blk fills a niche that neither 5.56 nor x39 filled before. It’s the best of both worlds. I’m more than doubling the mass of the chunk of lead going down range, but from an AR platform. I (probably wrongly) stuck with AKs for longer than I should have because I liked that larger chunk of lead. With 300Blk, I get to have my cake and eat it to. For the record, the internet warns us against trying to run x39 from an AR due to the tapered case not playing well with the straight walled mag well of the AR - YMMV.

One last thing, there is more to selecting a caliber/set-up than just “is it good in a fight?”. I actually have three 300Blk ARs and only two in 5.56. I let my paranoia run free as I work to ensure that a 300 round does not end up in a 5.56 chamber. Just something to factor in.

[JRB]

Didn't watch the video either - but some initial responses I have:

For the role suggested, I can't think of any limitations of the MCX 5.5in loaded with 110gr Barnes vs an 11.5-12in 5.56 or 7.62x39 except engaging targets at 300m+ which also gets complicated for any AK.

Louder and more aggressive is awesome when you're laying the belt fed hate at an enemy position and all that kind of hooah stuff.
Inside a building, unsupressed 5.56 from 11.5in and shorter barrels is really damn miserable. I have enjoyed a fam fire and a little shoothouse trigger time on a MK18 and with a suppressor it's fantastic, but without one and shooting live ammo indoors it is painful even with earpro. I found a regular 14.5in M4 still miserable but noticeably less miserable in the same shoothouse. 20in A2/A4 length guns are a distinct liability for indoor work and that's just basic common sense, but the regular old M4's work great indoors with sensible MOUT techniques. Same for getting in/out of most vehicles - M4's are short enough without much if any fuss IME.

Where the MK18 and other shorter 10.3-11.5in guns shine is when a good suppressor is added, because they keep the OAL advantage of the M4 while being substantially less miserable to shoot indoors or with limited earpro. On that note, 'hearing safe' 5.56 is possible from larger suppressors on 14.5-20in barrels but not on short guns. But the short guns are still worth suppressing because the gunshot is reduced to an unpleasant crack that doesn't kill your hearing like the sledgehammer-driven-icepick experience of an unsuppressed short 5.56 indoors.

Going back to .300BO, the 5.5in MCX with supers is about the same to my shot-out ears as unsuppressed 14.5-16in 5.56, which is another significant advantage vs the distinctly miserable blast from short 5.56 barrels.

Short AK's are fun but they're blasty with most ammo and some ammo is specifically very flashy out of shorter guns. Almost all x39 is loaded for typical ~16in AK barrels, so shorter barrels get really muzzle blasty/flashy real fast. Most muzzle devices on short AK's like the Krink booster and AMD-65 muzzle brake do little if anything for flash suppression as well. Then consider the clunkier ergos and optics issues(optics both in mounting sights, and in appearance as a 'bad guy' gun) along with the limited availability of duty-grade ammo for AK's like Winchester PDX1 or Hornady SST/Black/Amax etc.
Factoring together all of those considerations, and AK's of any variety tumble pretty low to the bottom of my list for serious defensive uses. I do love owning and enjoying them on a range though.

So the MCX is really a very effective option for this, especially with the 'dad bag' concealability. A 10-12in 300BO would only offer the advantage of being less ammo-specific for an effective load and it'd be less blasty than the 5.5in MCX.

On 300BO magazines, I insist on distinctly marking specific mags for exclusive use with 300BO. Having held and examined a post-KB 5.56 AR pistol, which KB'd because of a .300BO round being loaded into it by mistake and fired... there's no savings in cheap magazines that'd make me want to introduce that kind of risk.
The Lancer and Magpul 300BO specific mags do work very well and that makes it easy to justify there too.

In conclusion, I'd go MCX Rattler in .300BO, or 5.56 14.5-16in AR, or suppressed 5.56 10-12in AR. I'd leave the AK's as fun guns only.

[ECVMatt]

I read ".8" to 12" Barrel 30 Caliber Carbine" and thought of this:

82376

Sorry, don't know much about the short barreled 300 BO or 7.62x39.

Now back to my fascination with the chopped M1 Carbine.

82378

[okie john]

That video makes a number of excellent points.

He could have made his point(s) in a fraction of the time, but he's spot on.


Okie John

[UNM1136]

So I'm wondering a few things.

1. Is my original idea of having an 8" to 12" carbine in 300BLK or 762x39 have any validity? Seems like to make it worthwhile, you need to drop down to 8" because if you're willing to run a 12" barrel, the newest ammo in 556 probably with 62gr bonded probably does all of the things I originally wanted the shortie .30 cal carbine to do. It's just that 5.56 is still kind of poopy in an 8" barrel from cycling and ballistic effectiveness.

Firstly, you don't need us to validate your desires. In the USA at the moment desire is plenty of reason. Validity is a non issue. I have 5.56 because it is what I can carry at work. When my governor starts banging her gums this month about evil black rifles I will be getting AR receivers for the kids with intention to build .300BO or 6.5 Grendel guns for them. Both of those are legal for elk in most states, and teaching the kids the limits of the guns to keep shots ethical would be fun. If we were starting our patrol rifle program at work today instead of 15 years ago, I would be doing a lot of homework on what to issue; both guns and ammo. I think institutional inertia is a huge reason for 5.56, and it is not a bad one. But it is not the only one.

2. It seems like if you're a professional gun fighter or even a LARPer, then 4" of OAL shouldn't matter much. So if 62gr bonded 556 is really good at car penetration and intermediate barriers, then maybe running an 11.5" SBR in 5.56 is equal enough to an 8" in 300BLK / 762x39?

4" OAL is not an issue. We issue 14.5s and 16s with cans. Any real use gun should have a can, but I would not require it. All of my real use guns, including big and small game hunting, will have cans in the next few years. It may not be practical in all circumstances, but for many uses suppressed is better than not. As far as the equivelancy between 11.5/5.56/62gr and 8/300BO-7.62... you are stuck with what ya brung. Pick one, pick both. When the balloon goes up you may only be able to grab your pistol. What if is a game you can never win.

3. Am I right that out of an 8" to 12" barrel, comparing 762x39 to 300BLK supersonic would be about the same as each other? How about unburnt powder, am I right that it doesn't waste as much powder in a shorter barrel compared to 556?

You might be right. I dunno. I have no use for 7.62x39 anything. If I understand your question the efficiency of the round and wasting powder is not a decider. I really don't know how to quantify what I am thinking here. In 5.56 I want a 14.5-16 inch barrel, with few exceptions. If I were looking at issuing urban patrol fifles for my agency right now, 300BO would be a strong cartridge to research. Range, barrel length, zeroes, penetration in ballistics gel, penetration in common commercial building materials...

4. For the civilian LARPer with the budget to afford it, does it make sense to compliment an 11.5" 5.56 gun with an 8" 762x39/300BLK gun? Or is it just kind of silly?

Do what you WANT. Silliness is built into and OK with wants. Make yourself happy. Who knows, you may publish a thesis on .300BO vs. 5.56 in the SBR urban rifle. You may contribute hugely to the community.

For the purposes of this discussion, I'm disregarding the MCX Rattler with a 5.5" 300BLK barrel because the purpose of that gun isn't "we're doing CQB around cars" but the purpose is "we need a small compact effective gun that can hide in the smallest possible package, 556 doesnt work out of tiny barrels, so here we are with 5.5" 300BLK". I don't think anyone is intentionally choosing to start a fight with a 5.5" barrel Rattler. If they had a choice, they'd probably get an 11.5" 5.56 SBR.

Starting fights?

In other words, if you were going into a fight, and you weren't trying to conceal the gun in a small bag (in which case the 5.5" Rattler would win, so there's no need to discuss), is there a scenario where you'd choose an 8" to 12" barreled 762x39 / 300BLK versus an 11.5" 556 SBR?

Yes, plenty. Both professional and personal. But I am gonna use what I got, even if it is a 9mm pistol.... Really having a hard time puzzling this out...

My stuff in bold.

pat