First, check the caliber marking on the barrel to see if it reads ".38 S&W SPL +P."
Next, check the left side of the frame, for what is known as the "cylinder stop"(which is NOT the "cylinder bolt," that engages the notches around the cylinder). This is a small raised part that keeps the cylinder from sliding backwards off the crane/yoke when the action is opened - open the cylinder, and you'll see that its outside edge just touches against a small ledge directly above the trigger on the left side of the frame. On older J-frames, the cylinder stop is a round boss that is actually pressed through a hole drilled in the frame; it is split down the middle, and the forward half is ground away, leaving the rear half as a ledge to keep the cylinder in place. On the newer "J-magnum" frames, the cylinder stop is machined integrally as part of the frame, and will look like a reinforcing rib running from the left-hand recoil shield down to the bottom rear corner of the frame opening.
Also, the cylinder and frame opening of the "J-magnum" frames will be longer than those of the older J-frames, but you can't tell that without calipers unless you compare the two side-by-side.
As a side note, Dick Metcalf wrote an article in
Shooting Times(May 1998?) where he fired 2500 rounds of .38+P in a "J-magnum" Airweight Chief's Special AND in a slightly older "standard-J" Airweight Bodyguard - both guns came through unscathed, with frames and cylinder gap/endshake still well within factory specs. While I might be inclined to baby an Airweight J-frame made before the '80's, if it's a newer-production gun like my nickel 442 I'll shoot +P for familiarization and carry same with confidence. Check the extractor star - if it has the sharp, pointy corners on two of the flanges, it's the latest generation "engineering change" before the "J-magnum" frame became universal across the board. If all the flanges look the same, and you see a couple of holes for the locating pins in the cylinder, it's a bit older, and you'll need to check the serial # or "dash-#" in the model designation to determine the vintage.
