Are we talking the 5.7 X 28 uppers for AR's that utilize the P-90 magazines?
An expensive addition in an inferior caliber that is difficult to find and even more difficult to reload fed by expensive, albeit cool magazines.. I'll pass.
If I happened to have a few cases of ammo and a dozen magazines given to me, I might reconsider.
And..... +1 on that post.
JD