Hornady brass 40 f/s faster than Lake City?

I ran some identical loads through my chrono, i.e. Ran through same sizer setting, same bullet, same grains of RX-15, same OAL, and the Hornady cases ran faster than the LC loads. Any ideas?

What cartridge are you loading for? Possible that the Hornady has a lower case volume resulting in slightly higher pressure. My experience has always showed the opposite. Lake city has always given me more Velocity than anything else and why I choose to make most of my own cases for other calbers out of the stuff. 250 savage for example gives me an extra 50 fps when I used sized down lake city match 308 cases over standard winchesters with the same powder charge. Check the case volumes between the two different brass types and you will probably find your answer.

I am loading .308. I had read about the heavy wall and webbing of the Lake City brass so this difference in velocity has me confused. Is there a possibility the difference may be in neck tension?

Measure the water capacity on a few of each brass; the difference of internal volume probably accounts for this. Less volume = higher pressure = faster velocity.

Thanks! I was headed there next.

While peak pressure may be higher sustained pressure may be shorter reducing acceleration of the bullet. Powder choice is important in this regard.