气体调节器 should be gas regulator, I don't think there is any such thing as a gas adjuster?
For 瞄准装置 you wrote scope but I don't see any scope in your photo, is it supposed to just be some type of sights?
复进簧 should be recoil spring, again I don't think a thing such as a return spring exists.
The literal translation of 活塞簧 is piston spring, I'm not sure if it should be translated differently from that since the word I know for bolt would be 栓 or 枪栓. Also the drawing looks more like for the piston, in which case I think carrier spring is the term in English.
上护盖 might be an upper guard but maybe a dust cover for a scope to go on? I don't recognize the Chinese term. I think upper cover in English is probably not right, I'm not aware of such a term. The Chinese is as vague as the photo to me here.
See what I said before, trying to go off the drawing this 活塞 looks a lot more like its part of the piston set up.
The term I know for action is 枪机. 机头 I believe this is referring to the forend of the gun but I also don't think its the official term. The one I know for that 护木头. (机头 term is usually airplanes nose etc.)
膛室 is the term I know for chamber. Maybe 机体 is referring to the frame in general, but the term I know for that is 枪身. Again the term you have here I know for planes etc.
枪托 is the butt of the gun, so stock is fine.
弹匣 is the ammo magazine, correct.
I said all this off of basic gun knowledge, but terms might vary. As with any technical knowledge, I highly recommend becoming familiar with the parts of the gun in question in your native language and then finding the name for that term in the other. Guns vary a lot and a specific model may have a term others don't.
As it stands I'm not fully certain of the Chinese or the English here. The photo that doesn't actually label or display all the gun parts does not help narrow things down.
Hope this helps, if you are able to specify the model of gun or find a better photo of what you want translated than a much more detailed answer can be given.