Ok, so I have a cyma zm51, I know it's not much of a gun, but hey, it was free. I opened it up and it looks like no other bolt action internals I've seen. This is my first time upgrading a gun so I have no clue what all of the parts are called. The first issue I know needs to be resolved is where the barrel meets the bolt there I a rubber cylinder that keeps the bb from rolling out of the barrel, the issue is the one the factory put in is too small, the bb gets stuck and jams the gun almost every other shot. Can anyone tell me or give me a link to how to fix it or the replacement part? Also, there is a hole in the barrel, it is about 5/8 down the barrel towards the end of the muzzle, it goes all the way through the inner barrel and is lowering the fps. The space of the outer barrel is just enough for me to fit my ring finger without the inner barrel in it. Other than those two issues the gun works fine but not to the performance I need. What parts should/could I put in it to increase distance and accuracy. It comes out of the box with 350 fps with .20g. The top picture is if the internals. The second is the barrel where the hole is.the bolt catch. And the third is the bolt catch.