On my Gen 1, Gen II and my shooting buds, Gen 2 and Gen "3" Sig MPX we always have a huge (80fps on 900fps avg) velocity variance on the 1st shot over the chrono. The next shots are always with acceptable variation (15fps to 20fps). I can understand a lower velocity from a cold barrel (often i've chrono'd after a practice session), but not to this extent. Any ideas what could be causing this ?