I disproved this already back from 2009-2012 with my 16” Grendel. It seemed like people were being reasonable and accurate when making those statements back then, and a lot of dudes simply read it and repeated it without ever checking. I never wanted a 16” Grendel, but that’s what I ended up with after trying to check out from Midway with a 20”, then an 18”. 16 and 24 were all that were left, so I put a 16” in the cart and checked out. Glad I did now, because it exposed a lot of the BS about Grendel not being capable or comparable from the same barrel lengths.
It would be fun to do a side-by-side with short barrels, since I’ve been shooting the 12” Grendel now for 7 years straight. I don’t see a perceptible difference between my 17.6”-18” Grendels, though I can show the minutiae on paper.
I’m not seeing any ballistic advantages to the 6.8 from 12” barrels. The 6.8 bullets bleed momentum really fast due to how they are shaped.
Both of them have the same basic case capacity and when you shoot the same bullet weights, they are within 20-40fps of each other, which is lost rapidly by the 6.8 out of the muzzle and surpassed by the more aerodynamic 6.5mms.
It just is what it is. The one bullet that makes the 6.8 SPC II behave more like a Grendel is the Berger 130gr Classic Hunter with .490 G1 BC, but you aren’t kicking it out fast. Hornady 6.8 bolt gun data with 130gr bullets loaded longer than AR-15 lengths at 2.355” COL is only doing 2300fps from a 16” barrel.
If you’re truly looking at a bug out from LA kind of scenario, I’d just build another 5.56…. Two is one, and one is none mentality. Start working on training, and other needs before running down the “other caliber” rabbit holes.
Edit: Or build your second lower up as a complete rifle in 5.56 so you have a spare, and then as funds allow, build different uppers in various calibers to suit your fancy.
— break, break —
Re: Intermediate calibers: 6.5 Grendel’s a great round…very popular with the pig hunters in my neck of the woods for a good reason: It just flat works.
That said, the 6.8 (in SPC-2 chambering) seems even more popular with the shooting professionals I know…folks who eradicate sounders of feral hogs for cattle ranchers, run helicopter tours, etc. Have had many, many conversations with them on the efficacy of various rounds, and the consensus is that the 6.8 works better…but honestly no real difference.
Pretty small sample size though, and localized to South Central Texas where the conditions may differ than your AO and needs.
6.5 G is an awesome round, but 6.8 works better if you get it past factory 6.8 loads and into 6.8 SPC-2 chamber pressures — assuming your barrel was made to do so of course. All 3 of mine are built to SPC-2 spec.
If 6.5G is more available in your AO, I’d go that route in a heartbeat. I was agonizing over the choice between 6.5 and 6.8 myself several years ago, and wound up going 6.8 purely because a colleague wanted to build one and we could get a discount by buying more barrels together…and he had a line on a deal from a guy getting out of the game, so we scored a pretty huge initial load of 6.8 ammo and once-fired brass.
The new kid on the block is 6 Maxx, with similar ballistics depending on bullet choice, and it uses the standard 5.56 bolt (300 Legend parent case). Seems great so far, but there are tradeoffs depending on bullet choice vs. case capacity. Not a lot of data on the 6 Maxx out there so far, but it seems like it works pretty damn well, albeit not as flexible as the 6.5/6.8 offerings currently on the market. If you roll your own, this could be the best answer yet for small frame AR intermediate cartridges
—
If you truly feel you must get an intermediate cartridge (and you’ll get no arguments from me on that approach, LoL, I love ‘em), I’d prioritize a round that takes the same bolt for parts commonality. My picks (in this order) would be:
1) 300BLK - Primarily use subsonic rounds; suppressed with a nice 30-cal can for HD and signature reduction. 300BLK is very popular (availability), uses the same bolt, and shines in the short range environment; it’s basically a perfect round inside 50 yards or so.
2) 6mm Maxx - Also uses a common bolt, and much better ballistics than 5.56 at longer distances; I’d probably build this one as a DMR type rifle with an 18” barrel.
3) Any of the other popular small frame intermediate rounds (6.5 G, 6.8 SPC, 6 ARC, 7.62x39, etc.) that take a different bolt face, and usually require caliber-specific magazines as well; I’d get whatever’s most available/popular in your AO.
