Just got my S200 today but I cant seem to remve the end cap to fill it. I have some rubber grip matt and still cant remove it. When I try the air cylinder starts twisting round Even if I hold the cylinder right the end cap still won't budge.

Is is safe to unscrew the air cylinder fully from the gun and then try and remove the end cap? I tip toeing round this becuase the S200 manual is crap!

Don't want to ruin my gun or blow it up!