Ar15 pattern rifles, the better than 556 cartridge

Looking to build a rifle and I’ve decided on a 14.5p/w barrel length.

I’m stuck on picking a caliber, our state it’s legal to hunt game with a 223/556 but I’m after the round that is just better from hunting and defense standpoint.

What other choices do you really have other than 300 Blackout and 6.8 SPC II? I owned a 6.8 SPC Bushmaster upper and it was a joy to shoot. I eventually got rid of it because the plan to go hog hunting in my area on public land was recently taken away in Missouri. You can now only hunt hogs on private land. I did cry whenever I wanted to pick up ammo because it’s hard to find and isn’t the most affordable. You’re lucky to find plinking ammo for under $15 a box (20 rounds). At that point, I might as well shoot .308 IMO.

Love him or hate him, but skip around the 36 minute (feels like 5 hours) video that Nutnfancy put out about 300 Blackout titled 300 Blackout: Best Cartridge You Don’t Need [POU]. I do like the title of the video - Best Cartridge You Don’t Need.

Honestly, I’d say just stick with 5.56 and just use a heavier load like a 62 or 77 grain round that the pros recommend for self defense.


25-45 Sharps is my next buy. All that is needed is a barrel change.

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Another good general purpose hunting round in an AR15 platform is 6.5 Grendel. The other suggestions are good ones too. 300 Blackout is more like the .30-30 Winchester cartridge. 6.8 SPC and 6.5 Grendel are more .308 Winchester like but I think the ballistics are a bit better. I’m aware of .25-45 Sharps but I don’t know what the ballistics are like.

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If your set on a 14.5 then stick with either 5.56 MK262 77g or go with 6.8


6.8 SPC II is what you’re looking for. Word of caution, it is an extremely expensive round.

6.8 is very good at bucking the wind, and a very accurate round, which makes it ideal for gunting purposes. There’s no question about it being superior to BLK, Grendel etc.

With a shorter barrel the best options are things like super sonic 300BLK. I’ve gone the other way, I’m running a 18" barreled 6.5 Grendel rifle these days. The cartridge is amazing. Check it out if you haven’t looked into it. Otherwise, with a 14" barrel, you are probably better off with staying with 5.56.

I think “no question” is a bit generous. BLK, SPC II, and Grendel all have their strengths. Grendel will be the best for long range accuracy as it has the best bullet selection, BLK is the best for short barrels and suppressors, and SPC is somewhere in the middle. SPC has an incrementally smaller rim diameter, which seems to give it the edge on bolt durability over Grendel. They all kill deer dead though.

It is correct that they all have their strengths, exactly. I would say that Grendel and BLK serve a niche, whereas SPC would be the best alternative for 5.56/223 as a general service round. I would rearm the entire military with the LWRC Six A5 or SPR 16" Rifles and UCIW 8" Carbines if we’d switch over to SPC. BLK is overrated for what it does. It’s basically the same round as 7.62x39 and delivers similar performance, it only suppresses better. SPC suppresses fine as well. There is no doubt that SPC is superior to 5.56 in each and every way. The problem is cost, the established Class V chain and magazines. The only SPC mag I trust is Barrett’s. I don’t like Pmags because the feed lips crack eventually. Lancer AW mags or good quality steel mags by Barrett or HK are the way to go. If only more manufacturers would step into the SPC market, that might bring cost down. Competition is always a good thing. Not a whole lot of compatible optics for SPC either, which doesn’t exactly make it a viable option to replace 5.56 in the militart. Flip side is that Aimpoints are compatible with everything, but the SPC is a marvel of a round and you wouldn’t get max potential using simple red dots, making it a highly cost prohibitive move. SPC will never be our general service round and it doesn’t need to either because 5.56 is fine with nowadays offerings (SOST, 77gr SMK, TSX etc). Both the 5.56 round and the AR platform have come a very long way and I see no reason to replace them. They are here to stay. The AR-15/M-16/M-4 is a professional’s weapon. Western armies use it and their SF/SOF tend to prefer it for good reason.