Thank you both for your helpful replies, it seems I have an embarrassing but interesting outcome. I stripped the rifle down last night and measured the stock and metalwork separately. I was primarily interested in what I have read on several sites about the bottom metalwork touching the receiver, thinking maybe they are contacting in such a way as to cause rocking or insufficient clamping force instead of clamping solidly to provide an adequate platform for the barrel. (this didn't appear to be an issue as my measurements suggested there was some .023" clearance between the top and bottom metal bits) Despite pulling the rifle apart three times and careful reassembling, at one point removing the nasty split-pin pillar on the rear action screw, and every time using your technique Lantohorse, of putting it together with the magazine in place (Good tip!) it still shot badly.
So, here's the embarrassing and interesting bit about which I'd appreciate some suggestions! The Rifle is in 223 and I developed two 60 gr V-max loads last autumn using the OCW system that, the last time I had need of the rifle, shot into less than .3 minute. If anyone's interested, one used Viht's book max of 24.7 gr of N133, but I settled for the other slower, more comfortable but just as accurate 23.8 grains of N133 (both at a coal of 2.215") which is quite short and a compressed load. No pressure signs and an average MV of 3086. Anyway, (please stay awake!) I made up 100 of these rounds with five times fired and neck sized Norma brass, together with 100 brand new Lapua cases. BUT, I had previously made the 100 Lapua cases up into the 24.7gr book max loads that chronographed at an average 3200 fps. A blistering, very accurate round that was nevertheless a bit of a flincher. So I pulled the remaining bullets, about 85 and reloaded them to exactly the same specs as the norma load. These are the rounds I have been using yesterday and today, until I thought to take out and try the Norma rounds which shot impeccably back into .3 minute. Why would a brand new case using a pulled bullet shoot a group of between 1.75 and 2 minutes compared to a neck sized one producing .3? I still can't quite get my head around it. Anyway I am still considering bedding as a method of eliminating more variables. If you've managed to stay awake, I thank you. Answers on a postcard etc.................