Need help diagnosing diagonal grouping

[willyqbc]

Okay, reloading guru's, need some help here. A while back i bought a weatherby backcountry in 30-06 (bedded and free floated, timney installed). Began testing loads using a 200 grn Barnes TTSX and settled on 53.5 grns of H4350 @2577fps which was producing approx 3/4 moa. This group size was consistant with 5 shot groups out to 300 metres over several trips to the range.
Now..... I go to the range the other day just to confirm all is well prior to spring bear season here and i start throwing 2 1/2" diagonal groups. 3 seperate 5 shot groups, each on a 45 degree angle but not going progressively in that direction with each succesive shot. Did not pay much attention to where each bullet hit in my first group be definately took notice after that and they were landing randomly on that 45 degree line.

I don't think it is heat as it did the same thing when shooting 5 in a row as it did when i let the barrel cool between each shot. Everything appears to be tight on the rifle.

Any ideas what might be happening here to go from so good to so bad without changing anything (that I'm aware of).?? Was I doing something goofy with my shooting that would consistantly produce this?? What reloading issues would produce this????

Any help appreciated
Thanks
Chris

 

[howitzer]

Could be any number of things ,different rest ,copper fouling ,scope failure,primer change, powder lot change .Try to go back and check your setup.

 

[Lodi]

The forearm may be interfering with the barrel. Your range setup may be causing the stock to move.
Make sure stock bolts are snugged. If the scope has a parallax adjustment, make sure it is correct for the distance being shot at.

I don't recall how the mag box is set up on your rifle, but make sure it's relationship to the other parts is correct.