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I had originally thought the 6 ARC might be a good fit and it probably would do the job even on hogs, but you guys have all but sold me on the grendel, which would likely get an 18" barrel. I'm also intrigued by the various .223 case wildcats such as the 6x45 and really a 6.5 wildcat using the 223 case. I have 1000 .223 cases on order from Starline and using a couple hundred of those for a new wildcat is tempting.
SteelBanger:
I have already been down the path you are on. I currently own 6.5G, 6.8SPC, 5.56, and others.
I have seriously looked at the 6mm Hagar, 22-NXS, 257 Bobcat, various 6mm and .257x6.8's, and some others.
The thing people often overlook when they start down this path are the effects of the larger case head size effect on bolts. If you run a Grendel, bolt quality really matters. The 6.8SPC can also have bolt issues when you go cheap but, in my case, I am 100% on ARP bolts which have superior steel in them and I have had no issues so far.
In the end, the .223/5.56 case options give me ~98% of the other options for significantly less cost, assuming you stay with more 'mainstream' options.
The 257 Bobcat offers a lot of extra velocity for 10gr additional propellant charge weight but, a bolt and barrel is ~$700. The 6.8SPC wildcats are a whole lot easier to make and barrel and bolt costs are close enough to .223/5.556 options to not steer me to or away from them.
What I don't like about the 6.8SPC in an AR-15 has to do with how they fit the AR-15 magazines! Is it a deal killer, no not really but certainly less than ideal! I run hot and cold with bullet options in this caliber for performance and cost. My "hog" loads DO NOT WORK WELL ON COYOTES OR DOGS!
The .223/5.56 based
6mm Mongoose or 257 Ocelot both fit magazines much better IMHO. 5.56 cases are cheap and plentiful so no scrounging tall grass trying to find expensive cases with a lot of labor in them! To get a full powder burn with common loads, the Mongoose needs a 22" barrel and the Ocelot only needs an 18" barrel.
The .257x6.8SPC options will give me ~150FPS in the weights I will shoot it over a 257 Ocelot for what real gain? Ocelot - Better magazine loading and cheaper brass combined with a more efficient powder burn yielding 3000~3100FPS so, while not the fastest on the block and most brag-worthy, it will do everything I need with an easy trim and fireform.
The 6x45 is another solid option if that is the bore size and payload you want for your targets. Its strong recommendation is what got me to the Ocelot. Be sure to check out the 6mm Mongoose on the MDWS forum if you are thinking about the 6x45! For me, the toss-up would be between the Mongoose and 6mm Hagar from WOA.
