it should be a little over 500 but they are not all the same
the FPS spread is there claim to fame but is they are dry and need oil they will shoot slow and with a large spread
and it seems oiling once is good but twice is better
so the rifle could shoot in the 440 to 460 range and be normal
I have a 853 and when I got it, it shoot very slow and I was getting air on my hand and thought it was odd
it was missing a very small plug in the air chamber for lack of another name, I plugged with an grub screw, just a side story and the plug is not a part that can be ordered
hope that gives some insight