Danny, the smallest action A7 is the medium length and has a bolt face to suit the 308 based cartidges, hence 22-250 and up fit it. They probably don't make a 223 on the A7 because they have their bases covered with the Tikka in the mid range price bracket and Sako 85 XS action for the higher price bracket.
As Ryan mentioned you can't rebarrel a 22-250 to 223 as the 223 has a smaller diameter base of the case. You can't put metal back on to a bolt face to make it smaller to suit that case.
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