I have the same issue. My Oprod binds at about the same spot. What I was told was to check the inside of your oprod for any metal burrs or imperfections the spring might be getting caught on and file them off if there are any(gently of course). If not, lightly grease the spring and inside of the oprod and the oprod guide. In fact, make sure the entire system is greased properly. If that doesn't work, check to see if the oprod is binding on the barrel where it widens out and attaches to the reciever. If it does, you're probably out of index or the oprod is bent or the oprod guide is not properly aligned. If this is the case, you can try tapping the oprod guide with a dead blow hammer which ever way it's out of alignment but I wouldn't go too hard on it. This is only what I could find online and I only have experience with one M305 so far so take this with a grain of salt.
My oprod is bent so I have to replace it before I can use the black arrow. I'm just running with the stock oprod until I get the funds saved up for another batch of parts. It seems to shoot fine for now so that won't be for a while.
Hope that helps.