Shooting at 450 yd. prone over a ruck at a 12" steel plate, my first 3 rounds will group about 5" 4th drops 6" below that 5th drops another 6". I let it cool of a bit and the same thing happens. is this a bedding prob. or something else. Load is SMK 168 with RE15 in LC match brass. Also my trigger could use some improvement, who should I send the trigger group to? Roben.

Also could be an issue with handguard fit. After it heats up the handguards could be binding up. Happened to me. Make sure you have clearance between the receiver and the rear handguard. Fitted mine where the only part that actually touches the barrel is the clip itself. The front handguard should have a little slack front to rear. HTH

Your getting barrel tension on the top of the barrel from heat to the wood.  
Check to make sure that the rear hand gaurd does not touch the receiver, the barrel under the wood, nor the sides of the stock.  Check the front hand guard against the gascyclinder, they should not touch.
Also check the middle band and the stock front band.  Make sure that both are solid, and if needed, locktite the middle band to the barrel, and glass the front stock band to the stock.

Simple put, as the wood heats up, it streches and somewhere down the line, it is pushing the barrel down (best guess would be the front hand gaurd against the cylinder).  The only tension that you want on the barrel is the middle band/front stock band that pull the barrel down at a constant rate.  As for glassing in the receiver, the tell tale sign would be flyers as the receiver moves in the stock and changes the barrel tension from the middle band (read shots would not be more constantly downward pattern as the rifle heats up).

Thank you for your replies. The rear handguard is tight against the bbl. until the bbl. starts it's taper. I can also see that this area of the bbl. is touching the stock on both sides. Fore/aft handguard movement is about 1/32 of an inch. The front handguard is only 1and 3/8" long, no play fore/aft just a little side to side. Roben.

What should I use to releeve the stock and handguard? Would sandpaper work or do I have to buy special tools? Roben.