can i have a spring sniper rifle shoot over 500 fps with 30 gram bbs
No. At our field no gun will shoot over 400 fps and no BBs heavier than .25. Sorry
If you are asking if it is possible to make one, it is. However as Kalish wrote, they are not allowed at our Browns Valley field. I don't know of anywhere local that they would trust someone to use that high of FPS.
Why do you need 500 FPS with .30 gram BBs? Are you playing in open desert where you can fire 200-300 feet? Most Airsoft fields have cover limiting your range of vision to 50-200 feet. Over this distance there are other issues to deal with.
Looking forward to your response.