Far more useful than a chrony for reloading is the use of a bullet comparator, and determining the optimal jump for the bullet...JMO...
Your variations in OAL are inevitable unless you're loading to the ogive for best consistency.
Get yourself two things: Hornady LNL, OAL gauge with modified cases for your calibers (or make your own cases), and the LNL bullet comparator.
http://www.hornady.com/store/Lock-N-...traight-1Each/
http://www.hornady.com/store/Bullet-Comparator-Kits/