I had this very same problem a while back and this is how I fixed it.
I usually practice everyday, and at the start of every practice I noticed my arrows would go to the left of where I was aiming. But then, two or three rounds into my practice I would start focusing on my release, and my arrows would start hitting where I was aiming. So I surmised that the problem was my release, and I started putting extra effort into perfecting a clean release. But then later on, I noticed that I had to maintain an almost a perfect release on every shot, or my arrows would go to the left.
Then sometime later, I ran across OL Adcock’s website,
http://bowmaker.net/tuning.htm and read his recommended method of tuning arrows shafts. I’m not going to go into his full procedure, but one of the things he recommends is that you back off as far as you can, with the biggest/widest/nastiest broadheads possible, and shoot from the farthest distance you can, and observe the flight of your arrow, and the point of impact in relation to where your aiming, will really show you how well tuned your arrows are.
So, I bought some 3 blade Woodsmans from 3 Rivers, and backed off 35 yards, and my arrows in flight looked like I just threw a curve ball and was hitting to the left of where I was aiming every shot. No matter how hard I tried, the arrows would do pretty much what they wanted to do.
It was obvious to me that my arrows were not tuned properly, and the broadheads where magnifying my problems. So, I ordered up more broadheads in different weights and after playing around a bit with different weights, I only needed to move up 25gr. in weight to weaken the spine just a tad to fix the problem, and man what a difference. Broadheads would hit where I was aiming and the field points where even better.
Moral of the story, If your arrows are tuned perfectly, they will be more forgiving when you screw up on your release, or torque your bow. If not, they will magnify the problem!
For me, it was a combination of being over spined, and a poor release. I never realized that 25 grains could make such a difference. But when you are tuning your arrows with field tips, it’s almost impossible to see a difference in just 25 grains, you can see 50, but not 25.
If you know, that you know, that you know that you’re arrows are perfectly tuned, then that’s one element in the matrix of your shooting sequence you won’t have to worry about when there’s a problem.
Just my opinion I could be wrong!