Depending on the particular bullet, some actually shoot better seated away form the lands.
I had a similar issue with a Browning A-Bolt 280 and speer bullets I used to shoot. I started at SAAMI length, and tested one it chambered fine, so I loaded about 15 to test different powder charges, I found some wouldn't chamber so I stopped shooting them. I got home and checked them with the calipers, thinking maybe the die wasn't set or moved, but the length was the same on all of them. I attributed this to variances in the bullets. I seated slightly deeper, and never had any problems after that.
I have started shooting Swift Scirocco bullets recently in the same 280, and have had better luck on grouping getting further away from the lands. I am still in load development, so don't have any final numbers on length yet, but am getting closer to where I want to be. My shortest length I tried on Saturday had the best group, about 0.75" at 100 yds, so pretty good. I am going to go a bit shorter on a couple of test batches just to see if it gets better.
Different bullets behave differently in guns.
I also had to seat deeper on a 22-250 I have in order to use the magazine. During load development, I found a load I liked, but was only shooting single shot at the range. Once I loaded a few more and went back, I found they wouldn't clear the magazine properly, so again went slightly deeper to remedy this. I should have checked magazine clearance before the first batch of test loads, but I failed to do so.
Good luck on the reloading! Every rifle and bullet is a little different, so trial and error on reloading can be frustrating, but once you get to the sweet spot, it is time well spent.