Cant use the existing rear sight dovetail as there isn't enough space to fit the rmr between the chamber and the rear dovetail. Thats why a new dovetail needs to be milled out at the very back of the slide. From the smiths that i found that do offer this service, a glock style rear dovetail is milled because its slimmer.
See pics.
Compare to a M&P CORE rear dovetail location.
See pics.
Compare to a M&P CORE rear dovetail location.
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