Nothing new there, LS308, most rimfire ammo is just like smokeless powder, there can be subtle differences in performance between lot numbers that make a difference. I always advocate buying small quantities until you find ammo that shoots good, then buy more of the same lot number. When I got my first Hmr, I drove 80 miles round trip to get more of the same kind of ammo, Federal Vmax, only to find out it didn't shoot near as good as the first batch I bought which was no longer in stock locally. Many, many RFCers buy their ammo by lot number the same way. That said, it seems that Hornady ammo is by far the most accurate in general in most guns, and I have to agree with that, it does shoot well in 3 of my 4 hmrs even with lot variance consideration.
Tim