Use a long SDS dril the same diameter as the pilot of the core drill, then drill right through the wall, use the core drill to say a depth of 60mm then drill from the other side of the wall , this will avoid unsightly breakouts.
Most of the cores you drill disintergrate as you go , so pulling out every few minutes releases the debri.
Any that don't break up you just tap with hammer and bolster and remove.
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