BudsGunShop.com - Caliber and Magazines.

223 vs 5.56 I'll answer as short as possible. The throat or leade on the 5.56 is slightly longer on 5.56 x 45 round. Reason, military production runs and use. When a rifle is in less perfect operating conditions and can't or doesn't get cleaned the looser tolerances may keep it running. The 5.56 x 45 round has looser tolerances on overall length, bullet seating depth and powder charge. If all the variables are on the maximum then you could have blown out primers that could ruin a day at the range. The 223 has tighter tolerances in both chamber and cartridge dimension. The 223 wylde chamber solves the problem by increasing the throat dimension while still keeping the tight chamber. Yep, the magazine should fit just fine.

If the barrel is a 5.56 s 223 then you can shoot either ammo. If it was a 223 then it would not be advised to shoot factory 5.56 ammo in it. This is because the chamber in the 223 is slighter smaller and will not allow the case to expand as much as the 5.56 chamber. The 5.56 ammo is also more abundant and cheaper on the norm.

First answer, the caliber it's chambered in, will fire .223 or 5.56. both of these rounds are 22 caliber, meaning the bullet is the same diameter as a .22 long rifle, but is a heavier grain and has more powder.
Second answer, yes, as long as the magazine is in a .223 or 5.56 chamber, it will fit in your rifle. Hope that helps.

This is chambered to use 223/5.56 (the only difference is about 5 grains of powder and a slightly longer leade in the barrel), Yes, the mag will fit.