Strange, I just checked it again, I put back the 450M with the shim and it nice and firm no movement like it ought to be, then I put the .243 back on and no more movement, hmmm, something with the latch I guess,
I'am going to try it this week end, I tightened up the scope mounts screws & checked the scope to be level and I used a friends magnetic bore sighter vs my laser bore sighter lets see if things improve.