Interesting that your ES/SD increased by so much with BLC-(2). I use the same powder and 75 grain Hornady. I am loading the same 26 grain charge you tested with a bit more velocity, CCI 450, Lake City 2021 cases all from the same batch, 22 inch barrel. My spreads are much lower. SD was 9fps if memory serves me correctly. You are correct though that the 26 grain charge of BLC-(2) is compressed at standard mag length for an AR, but only slightly in my cases. With my bolt gun though I am loading a little longer.
Are all of your Lake City cases from the same batch? Maybe my longer barrel and 223 Rem chamber are why my spread is so much better, but who knows.
So my LC are sort of mix and match. I considered sorting by weight however I was not feeling it at the time and just sorted out 100pcs with the same year LC 19, and put them in a reloading box.
As far as the brass goes it was once fired when I got it and it was in fairly rough shape smashed case mouths big dings in the shoulders and sides of cases. From what I was told it had most likely gone through a belt fed machine gun... I selected brass with none to minimal case dings for my batch of 100. Did a wet tumble, full length small base resize and trimmed. some of the brass was a touch hard to size, seemed a little bloated if that makes any sense.
One other note, I did put a firm crimp on these using the lee factory crimp die. I do the same for all my ammo going through ARs. Not sure how that would effect SD/ES, but it is something to consider. and something I need to test at some point.
I did notice a lot of soot on the brass after firing. Filthy dirty, not really sure what that indicates but it seemed a bit inconsistent with some of my other loads. I am hoping to get an annealer this summer. that might help things a bit.
Your longer barrel may be giving you better consistency. I have done some testing with my 38spl snubbie in relation to powder burn rates and consistency. what I found is that, faster powders provide less velocity, but burn more consistently. while powders that provide the best velocity, often have high SD and ES due to not fully burning in the barrel.
As I understand it compressing powders can also slow the burn rate which could account for the less consistent velocities as well.
But over all I am happy with the 25.2g loading. The velocity is within the acceptable range for what I was trying to accomplish.
