Why do you not want both screws torqued the same?
Chassis stock 101:
Most receivers are cylindrical in shape. Most chassis systems are a "V" type wedge. Pretty simple to envision how it all works. Two surfaces bear against the cylinder forming tangent contact along the length. Easy enough to understand.
The rub:
Few receivers are as simple as a pipe. Due to style, we like to see the tang feature of the action narrow into a visually appealing wedge type shape. Not all the different from an old broadhead on an arrow. This is where the wheels start to fall off. The tang narrows and because of this at some point, the back end is going to be hanging in space like a diving board over a pool. If the rear action screw is behind the last point of contact we end up with a lever. The stock now acts as the fulcrum (pivot point)
This can be easily demonstrated. Remove the front guard screw and tighten the rear only. If the action starts to levitate off the stock, you have this condition. This can cause some performance issues in terms of accuracy and function. I've had guns come through here where the receiver was bound up so bad the bolt didn't want to run...
To resolve it we have 3 basic options:
- Bed the tang with a resin system
- Alter the screw torque so that distortion of the receiver is avoided/minimized
- Add a contoured pillar*
*pillar. This is my preferred method. I locate the rear hole. Drill/tap it for 1/2-28. Turn a length of brass and thread it. Poke a hole down through it. Screw it into the stock and lock it down with epoxy. Once cured I come back and contour the pillar to the same radius as the receiver. This way the tang is directly supported.
Note: Not all chassis systems suffer from this. The Cadex stuff seems to address it with the use of embedded dowel pins. I know the late model mini chassis from Manners now has a boss feature around the rear hole. Its doing the same basic job that I've done to correct the older/legacy type AI stocks.
Bedded stock 101:
If the stock has pillars you should never need to exceed 50 inch pounds of guard screw torque. In fact, 40 inch pounds will do it if using SS guard screws with a 28 pitch thread. Install screws DRY. No oil on threads, no lube on the heads of the fastener. You want a certain amount of "sticktion" so that they fend off loosening up from vibration.
Tighten the screws to the same value. If you cannot, its because the stock was not bedded correctly. I would check the thing over, the trigger well in particular, to ensure a safety lever isn't rubbing somewhere. Magazine boxes must float inbetween the action/floor metal. DBMs must not contact the receiver anywhere.
Hope this helps.
C.
