Colt AR15 / Sporter 9 rnd Aluminum Magazine

So, you live in one of those states?  Maybe you need this.  It has the same feel as a 20 round mag, but clearly shows that you are not illegal.  Why not 10?  Hell, maybe Colt figured the next stupid law would be to ban 10 round mags.  

Works with .223 and 5.56 NATO