While what you did improved the accuracy, I don't agree that it was the right way to go about it. There are small protrusions molded into both sides of the receiver channel that mate into small pockets milled into the receiver sides. I believe the reason these rifles are having accuracy issues is because these points are not firmly mating together to hold the rear of the receiver solidly in the stock. Instead, as you found, the rear of the receiver is wobbling on the block that contains the magazine catch due to tolerance stacking. What you did was minimize the movement of that block, and hence the rear of the receiver, but you also raised the receiver even farther out of the stock ensuring that the stock cannot mate directly with the receiver as intended. The proper fix in my opinion is to bed the contact points at the sides of the receiver.