Hello, I am about 1 year into long range shooting. I have a remington sendero in 7mm Mag with a nightforce scope. The first year of owning my sendero it shot .5 inch groups on a clean bore (first dozen shots all together) then as barrel fouled they spread to about a inch at 100 yards. Now (a year later) all of a sudden my groups are drifting about 1.5 inches left to right. The first shot on clean bore is 1 inch right. Then second is about 1 inch left of target. Then following shots drift about .5 inch right and stay there for about 10 shots. My elevation of shot is always perfect but now my groups drift on the windage. I could really use some intelligent advice on what has happened. Did the barrel just change? I am not shooting on a hot barrel. Wait for it to cool each time and have exact reloads that have not changed. I have duplicated this three times now at different settings/shootings so I know it's not me. I just don't know what the problem is or what could have changed.