Well basically the piston is grindinf/scraping the inside of the cylinder. When i cock it back its kinda easy but grinding. Then when i go to push it forward back into place its almost impossible to push forward. Thats because its grinding the cylinder. I cleaned out al the grease because it was black. As i bought it off someone. And after a bit of research i came to find out that the piston,spring and spring guide have been upgraded with the utg upgrade package. Its all alluminum except the spring. The gun was working fine when i got it. But after i cleaned it it was scraping. And i didnt put any lube or grease in either. Is that the problem? Also what lube or grease am i supposed to use. Some peoe say pure silicone, some people say white lithium grease. Personnaly i think the grease woll work better because its thicker and if i just use silicone itll just wear off because its so thin. And grease would be there forever. And the entire gun is almost metal. The entire chamber is metal where the problem is. Excep one o ring. Please help. I just bought this gun.