In order to go from a 7MM-08 to a .223 you will need a .223 bolthead. You may also want to change out the front baffle from the standard one you have, to the "extended" one (for a shorter bolt throw).
If you want a repeater, you will need a new magazine and follower.
The bolthead you have now will handle the .22-250, or the .243
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