I had a 45 colt Vaquero which did the same thing. I thought it was my trigger pull. I called Ruger and explained the problem to the Tech and he instructed me to do a few simple things and if that was not the correction he would send a shipper and give it to a Tech at Ruger to fix. He wanted a couple of 5 shot groups shot at 15 yds with 250 grain Winchester Round nose cowboy loads. It seems this is the round they use to sight in and function fire their Vaqueros. If it was still left and low put it along with the fired groups and send it back to Ruger. It was still Low and left. I sent it back. Six days later my gun was back with a list of replacement parts which included the barrel, and trigger parts and a trigger job from Ruger at no charge. Shoots at POA now...