I did that for a friend's 788, his was re-bored by RKS. The mags (he had a few - from the .308, the 22-250 and one other i cant recall). They all needed a little tweaking in the shoulder to neck area. I tried tapping out the crease a bit and then tried using a large long reach pliers to push out the crimp, but what worked was a dremel / file to slightly, and I mean slightly, grind out some of the crease ridge of the mag to allow the wider neck.
After that, I found that it did not take much to get them to feed smoothly and not get hung up on the mag shoulder.
Some of the different calibers of mags have a different length shoulder. If you stay 308 to 358 you will find it easier.