I was wondering, is there actually a purpose to the filling piece that attaches under the air tank inside the stock?(pictures below) The air tank doesn't make contact with it so is it just an "internal weight"? Are there any consequences to removing it?
Here's a suggestion. Take out the back one. Leave the front one in. Now put the equivalent weight of the back one in lead and attach it as far back on the rifle as possible. The opposite side of the cheek piece or under the cheek piece if it is lifted a wee bit works well. If the buttplate is extended, make some lead plates - or steel - to match the weight and use them as buttplate spacers.
This will bring the balance point back considerably and hopefully will mean the balance point is now behind the support hand. If it does exhibit that tendency the shooter will find it a hell of lot easier to cradle the rifle in position. Too often I see rifles that are front heavy and the shooter has to use their body like a crane to hold the damn thing up.
