Something you will want to do, since you've been shooting 38's in it. Give the cylinder a good cleaning with a bronze brush to get all the carbon and lead out of it or you may have problems extracting the 357Mag cases. Also, M19 can use 357Mag, it's what they were designed to shoot BUT as a general rule LEO's would practice with 38's and carry 357's for Social Work. The Forcing Cone is suppose to be the "issue" with em' so keep an eye on that and I think you'll be fine.

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S&W M642-2,
ATI 1911a1, 4.25"