Originally Posted by
Sanch
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...