This is what I shot today...I also shot some factory 300 WM, and couldn't get my LabRadar picking up my trigger...there was another guy there who was dialing in 22-250 to take 'yote hunting in Colorado. I think it was a ruger varminter, a fairly inexpensive rifle.
Let me explain this picture, it had 8 loads with H4831, with Hornady 130 CX bullets, in new brass, those are the cases on the 2 left rows. Anything without a primer in it was not loaded or shot, and in the middle there are 13 loads using new brass, and 12 loads using once fired brass in my chamber.
This is my unscientific conclusion. The once fired does fit my chamber better, easier to close the bolt. The new brass is a tad tighter to close.
I didn't have a target to dial in with, and couldn't get my LabRadar working with the trigger...so the fact I had the tripod stable didn't really help...I also shot 3 rounds of Nosler 180 E-Tips, and 3 rounds of Barnes Vortex wtih Hornady 180 CX bullets, both in 300 WM. After I realized I could have bore sighted and dialed in on a closer target, but didn't think about that, and need to load more ammo now. All of this brass is fired now, and the cases without primers have been sized. I only sized what I loaded, and only had 25 Barnes 127 LRX bullets left, hence the 13/12 split.