I am wondering how much better a 12" 6.5 Grendel could be than a 20" 5.56 with proper bullets?
What velocity, bullet and all that stuff?
Not much. Probably falls flat on its face where a heavy .223 cal would surpass it. Id be looking at something like the 77 TMK in the 556 and call it a day.
Nah, see my post above. The slow Grendel drops more but outperforms heavy 5.56 in pretty much every other way, even from my short 12.5" barrel. I didn't think that would be the case until I built one and started shooting it, but time behind the rifle shows what's what.
That 243 must have similar case capacity as my 6WOA .
Case capacity is similar, but the short Grendel case leaves a lot more room in the magazine for long bullets, which is important for a long range gun. Long VLD style bullets are no problem at all in my 243 LBC with ASC mags; my 95gr VLD load above is only seated out to 2.235", with room to go out to ~2.310" if I need to.
I would guess that same bullet or anything longer in your 6mm WOA would choking up pretty close to the ogive, if it fits at all; are you able to use it?
Keep in mind the 6mm Grendel-based wildcats are essentially the old 6mm PPC accuracy champ set up for heavy bullets and with the shoulder bumped forward slightly.
The other part of my preference is that I've had much better luck with quality and longevity of Grendel brass than I have with SPC brass.
