I believe the NP2 piston is too large in diameter to fit into the NP compression tube. If the existing piston still works well, keep shooting it. If it fails you'll know it. THAT is the time to order a replacement.The GRT III makes a fantastic difference in the way a gun shoots. In the course of playing around I ordered and installed an NP2 trigger assembly into my Nitro Venom. After a bit of work I preferred it to the GRT III.
I have the CBT NP2 trigger in a Crosman Summit Ranger NP 2 Rifle. I have the standard Crosman trigger in a Crosman Vantage NP that is about 5 or 6 years old. I have CDT GRIII Trigger in a Benjamin Trail NP XL 1100. I have a new Crosman RedTail with a standard NP Gas Piston and Standard Trigger. The worst was the Vantage, that I bought right after Crisman introduced it. I did the Screw Mod to Improve that one. The New RedTail Is a lot better and they must have made improvements. Of all of them I like the Clean Break Trigger in the Summit Ranger the best. The RedTail is #3. and the CDT GRIII In the Benjamin Trail NP XL is #2 I hope this is of some help to you. I replied because I had All 3. Best Wishes - Tom