John Joseph
I like an IWB holster, like this DeSantis SOF-TUCK, for my Model 649 and Model 638. I have found that an IWB holster like this does a great job of concealing my revolver and keeping it in place without the need for any sort of retention strap.
The Bianchi 55L Lightnin' belt holster in Sistema1927's post has the retention strap in a much lower place on the holster (unlike the typically higher location above the hammer using a thumb break snap closure), in order to accommodate the hammerless design of the gun. The snap closure is supposed to be released by your middle finger but this might make for an awkward and difficult presentation of the gun while trying to accomplish this.
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