I'm not sold on the Spear because of all the issues with the Spear itself. Being able to flex the handguard out of place and have it stick physically to the barrel is ridiculous for example.Anyone who has ever slugged a steel plate at any kind of distance with a .308 versus a 5.56 ought to know there's a "there" there with the big boy calibers.
You can do a whole lot with a good 5.56 gun, but when it's time to punch through intermediate barriers or reach out and nail something, there is no replacement for displacement. There's a reason machine guns still shoot full rifle calibers and not 5.56. Not all that is relevant to civilians or police, but out in the downrange world you use bullets to wreck a lot more than just flesh.
I might not be sold on something like the Spear as general issue, but until someone makes 5.56 exploding smartrounds, full power calibers aren't obsolete.
Plus I think they should have looked at the 6 arc instead. It's already a wonderful round but I don't think anyone has even tried to make an AP version or any real 'military version' of it.