Did not feed at all from the left rail; bolt ran over the top of every single round. Mag box needed to be tigged to keep it from flexing, plus feed lips tweaked, plus mag spring located in place.
On the ADL style boxes, I make them a solid bottom. This is a big help with flex and keeping the spring where it needs to be for feeding. Any spring spacer needed gets epoxied to the floor of the box once it's length get worked out. It helped the feeding on both CLR's I've owned, too. -Al
