I had a long conversation with a Border Patrol Captain back in the mid-80s about the 110g 38 Special +P+ rounds they carried at the time. He was envious of me, a lowly Sheriff's Deputy, because of the Colt Government Model I was carrying. He told me of several shooting incidents involving BP using that ammo in which it did not perform as advertised (claims of the Fed Gov bureaucrats). The Captain told me he had choreographed it personally and it produced an average velocity from his 4" revolver of just over 1200 fps. To say is was a way to hide Magnum performance is a considerable mis-statement.
PS: I called Star-Line asking about +P brass and they told me it was exactly like other 38 Special brass except for the marking. I'm willing to bet the +P+ brass is the same.