The light primer strikes sounds like he might have lightened the hammer when he did the trigger job, and got it too light, or possibly he weakened the hammer spring to lighten the pull somehow.
The stovepiping sounds like it could be the ejector. It doesn't matter that it has only fired 100 rounds, other than the fact that it isn't even broken in yet. Are you cleaning and lubing according to the military spec manual, and only using CLP? Have you lubed the ejector according to the manual? If all else fails, and your lube procedures are up to spec, then some people find they have to replace the ejector spring.
You say it does this with only the adv. line 20 rnd. mag, but not the 10 rounders? You might try using a few different mags. The 20 rounders are typically the most reliable, however.