Anthony,
6mm WOA is a great cartridge. The basic rationale behind the 6.8 SPC (the parent case) and the 6WOA (the necked-down wildcat developed by John Holliger at WOA) is to optimize the case capacity and ballistic capability of the AR15 platform. There is only so much you can enlarge the bolt face and enlarge the cartridge (over the .223), still staying within the limitations of the AR. The magazine size limits the overall length of the cartridge, and the aluminum upper receiver limits the overall pressures and forces that can be contained before excessive flex and metal fatigue occur.
If you are building a bolt action rifle, then you don't have these AR-specific limitations. Now you can think out of that box.
One consideration: the rim diameter of the 6.8 SPC/6WOA is .422". I'm no expert, but I don't think that this is too common, and you might need a custom bolt face. Why limit yourself to this case diameter? Why not use a "standard" such as the the bolt face designed for a .473" rim of the 22-250, 243, 308, 30-06, 6BR and many others?
You want a short hunting/target rifle and are considering a 6mm. OK, this means you are looking for small game - varmints, coyotes, small deer or similar. A .243 would do this, but you probably don't need that much powder capacity. How about a 6BR? Very short case, standard .473" case rim, excellent brass available and more powder capacity than the 6WOA. The 6BR is known for its superb accuracy. If you want even more powder capacity, you can "wildcat" the case up to a 6BRX or 6 Dasher very simply. I think that the 6BR will achieve 2,900 to 2,950 fps with 107 gr. bullets, and way more than the 2,800 fps mentioned with the 95 gr. bullets. The 6BRX and Dasher will achieve well over 3,000 fps with the 107 gr. bullets. These velocity figures assume a 28" barrel, so they would be slightly less with a shorter 20" barrel that you mentioned. But still more that you would get with a 6WOA.
Since you appear to be willing to "wildcat" to a 6WOA, you might consider another 6mm wildcat, David Tubb's 6XC. I think that this is basically a shorter version of a .243. This would have a larger powder capacity than the 6BR or its wildcats, and much more than the 6WOA, but this is still would need a relatively short action.
Even a .243 would make an excellent small hunting or target rifle. I don't have any experience with it myself, but I'm told that the barrel life of the .243 is limited because of the large powder capacity and the small caliber. That's why I would favor one of the others - 6BR or its variants, or maybe the 6XC.
As long as you are considering a "non-standard", or at least uncommon .422" case rim and bolt face size, why not consider one a little larger, for more powder capacity? The .44" case rim/bolt face diameter is shared by the 7.62x39 (AK-47), 6PPC, 220 Russian and 6.5 Grendel family of cartridges. Robert Whitley has developed the 6mmAR, a necked-down 6.5 Grendel. There are variants, such as Whitley's 6mmAR Turbo Improved, or the non-proprietary variant, the 6RAT. All of these choices would achieve superior ballistics, compared to the 6WOA, but still in a small package.
Again, however, with a bolt action instead of an AR15-based rifle, I would go up to the .473" case rim/bolt face of the 6BR or variants, or the .243 or 6XC.
Just my $.02, any other thoughts? I love the 6mm rifles and feel that they are perfect for target shooting or hunting. I have a 6BR bolt gun, and one of my favorite bullets is the 95 grain SMK. The 95 Berger is at least as good, although a little more expensive. The 6BR and 95-grain bullets are a perfect match.
Randy
