Waveski:
Your Model 586 Distinguished Combat Magnum was manufactured in 1983.
It is subject to a recall. With some magnum ammo the primer can flow back into the firing pin bushing, locking up the gun. Under the recall S&W will pay shipping both ways and install a new firing pin and bushing. If the gun has already been modified there should be an M stamped near the model number.
ljnowell:
You have a .38 Military & Police Model of 1905 4th Change manufactured Between December 1920 (serial number 358xxx) & 1927 (serial number 561xxx).
If there is a Made in U.S.A. stamp on the right side of the frame, then 1922-27. If no stamp then 1921-22.
It predates the positive hammer block safety introduced after a fatality with a dropped gun in 1944. Treat it as a 5 shooter, leaving the chamber under the hammer empty.
It has a heat treated cylinder, so is theoretically safe with commercial .38 Special ammo, but S&W do not recommend use of PlusP ammo in these earlier guns.