YES, you can open it carefully but keep hold of the barrel and keep your finger off of the trigger until you have the spring fully compressed and the gun closed again.. NEVER dry fire a spring gun or you can cause severe damage.
Once cocked...not..a good idea to try and open it. With spring under full power you are asking for a problem!!! If a small springer, lowvpowered you might get way with a good compressor but a big RWS or an R1. Will be a big hazzard. Better to dry fire it then replace the spring and seal.
Posted this in your other thread and will again because you said Chinese and thought it was like the Diana 350, which would make it similar to the Xisico XS28M.
Personally, I'd say do nothing more until you call Mike at Flying Dragon Air Rifles, explain everything and see what he says. He knows the Chinese stuff inside out and should be able to tell you what's going on and how to get that thing to safely release so you don't, as a friend told me, become another "Don't do this" thread. He might also have whatever parts you might need to fix it once you do.
Best time to try is between 9am to 12pm CST: (515) 924-3699
I think you're right. I forgot I did this about 15 years ago. To get it uncocked I took 2 large bath towels and folded them up and laid one on top of the other on the ground. Then I took a small rubber hammer and punch pin and punched out the first pin in the trigger housing. Then I grabbed hold of the gun as tightly as I could with my left and and with my right hand I punched out the other pin in the trigger housing. That was the only was I could figure out how to keep from breaking the entire trigger housing. Because something has came out of the trigger group, because normally the problem you have out of springers is that they won't cock at all, not that they won't fire. Anyhow that was my one time I dealt with that issue. I have a spring compressor, but to this day, I would still do it the way I did it years ago. It also would be easier if you had someone to help you. This all assumes that the gun is similar to an RWS 350.
I have a spring compressor as well but I think I’m gonna use a C clamp and house the spring in Wood. I have one clamp with a 12 inch screw that will easily absorb the extra spring. Crow