Make a homemade comparator. Check your fired brass or your loaded ammo. Compare. The 223 case has to be square on both ends. The end touching the shoulder is beveled with a chamfering tool. The stick is to keep the caliber up off the primer & to keep the brass in alignment. Dont measure on the primer. When you get repeatable measurement within .001" you will know you make it correctly. Put an index mark on the modified brass, place it in the same position for each measurement. Took about 1 hr to make & didnt have to wait for one to be shipped. Still using it today.