chronograph question

[supertech]

I have an Alpha Master Chronograph and noticed that it seems as if each shot recorded by the chrono increases in speed. I have noticed this on all ammo I've shot through it, .45, .308 and .223. It is positioned 10 ft from muzzle while using diffusers on clear blue sky days. Is this normal? Any tips?

[cassius]

Might be an actual increase in velocity, do you leave your ammo out in the sun during such an exercise?

[merritt]

also if this is from clean barrels they should change velocity as they start to fowl

[r08ert209cali]

how much increase? also the barrel is warming up and getting larger, which could possibly be a change in friction causing more pressure.