1st rounds fliers...what causes them?

[opngrnd]

I've put together a new build meant for accuracy, and have noticed a trend for the 1st round to shoot outside the rest of the group, usually high and left, or high or left. Basically, notably outside the rest of the group in the 9:00-12:00 direction. The remainder of the group is usually very tight.

Build:
Sionics 18" barrel
Geissele Mk8 Rail (used certified torque wrench and followed instructions)
Vltor MUR
Sionics parkerized BCG/CH
BRT Covert Comp(barely above hand tight)
Sionics assembled Lower
Magpul UBR Gen2
Sprinco Green Spring A5H3 buffer
Geissele SSA-E trigger
Vortex HS-T 6-24

100 yards:
Attachment 52205
Attachment 52206

200 yards after firing 5 rounds on steel, then shooting paper:
Attachment 52207
Attachment 52208
Attachment 52209

My buddy built an identical rifle, minus the handguard and scope mount, and is seeing similar results. I asked him to fire the first round of his magazine into the berm before firing his five round groups and his group size dropped substantially.