I've just ordered a CPO Sig P239 in 40 cal, with the intention of shipping straight back to the Sig custom shop for an SRT, and hand fitting of the 357 Sig barrel. It will be an edc. Do I need to have it re-sighted for 357? I've heard stories of different POIs, so was thinking of having it re-sighted with 25 yard zero in new cal. Will this be an added expense, and will it be necessary? I am not sure how the change in POI is accomplished. Any input would be appreciated.