I have a Model 70 6xc completely built by GA Precision (trued action, bedded, with muzzle brake) with a 1:7.5 twist Bartlein barrel. I have been unable to find a load with small extreme spreads and consistent accuracy using RL17, H4350, and H4831SC with any bullet or primer so I tried faster powders. IMR 8208XBR and Varget both had very good extreme spreads of around 12fps with 107 SMK's and 105 Berger Hybrids. When developing these loads it was very windy and I had horizontal stringing which I attributed to the gusty wind. I shot the best loads again on a calm day and still had horizontal stringing. The groups averaged about 1/4" or slightly less vertical with 1/2" to 1" horizontal. I loaded up some H4350 with 107 SMK's just to see if they were also horizontal stringing (I have shot this load before with mediocre accuracy and extreme spreads larger than I like but it was somewhat proven). It was not a great group (.59" for 5 shots) and the ES was 38fps but this load did not have horizontal stringing. I checked the rifle over. Barrel is free floated very well, magazine box is not binding, removed scope and checked bases, checked scope rings, and checked torque on action screws. Everything on the rifle checked out. Varget and IMR 8208 XBR have been the only powders that have had consistent velocities for this rifle. What would cause these powders to string horizontal? Is there anything you guys think I should try? I've put over 400 rounds thru this rifle trying to find a load with good accuracy and consistent velocities and I am getting FRUSTRATED.