Hi Phil and welcome. You can fire +P in moderation. A point that many miss is +P = more powder which recommends a minimum of 4 inch barrel for the powder to be fully burned. In a short barreled derringer, you only get more muzzle flash, boom and nowhere near the performance you think due to said unburnt powder. Stick with standard pressure ammo in derringers for faster follow up shots. That extra +P performance out of a 4 inch plus barrel shrinks down dramatically in a derringers barrel. You are better off with ammunition optimized for shorter barrels. Cheers, stay safe and enjoy!

Per the owners manual - No, because: "(+P) Plus P ammunition generates pressures in excess of standard ammunition and are unsafe for the Derringer design. DO NOT use (+P) load in any OLD WEST manufactured Derringer." That being said, these guns are all the same frame with different barrels and the company makes 9mm models which should still generate higher pressure than even the hottest 380.