I picked up an AA S400 lite recently. I like to raise the gun[no scope fitted]and open my eyes just as it fits into my shoulder. I then open my eyes and look down the barrel. If the rifle feels comfortable and i can see straight down the barrel,it fits. If i have to cant either way, it dosent fit. With the lite i had to move my head to the right to line up with the barrel. Question..........As i will be using a scope does does it really matter,as my head will be a little higher and maybe back a little. Its just that i like the rifle and from memory i think all the 400 series seem not to fit without a scope. At the same time i tried a HW 90, which seemed perfect,my eye was looking straight down the barrel. Again the fit parameters would alter once a scope was fitted. Or should you always test for fit with a scope fitted.