Do,you sort and keep track of how many times fired ?
Yes , I remember guys saying no need to separate either rifle or pistol . I had been loading rifle for a few years before loading pistol . So when I started loading pistol at first I separated the brass to keep track . About 6 months in I decided to just throw a bunch of mixed brass in to one lot and load them up . I instantly noticed there where differences in the brass . Case wall thickness being the biggest issue . If I had set my crimp to lightly crimp one of the thicker walled cases . I would get no crimp on the thinner walled cases and the opposite if set the crimp die to a thin walled case . I could feel the difference when I sized the cases as well as other things .
All that bothered me so much I could not keep mixing my brass . OK I do have mixed lots of pistol brass but it's still separated by thin walled and thicker walled cases . That alone seems to give me a much more consistent case prep and loading experience .
Just recently I came across a large stash of mixed 223 & 5.56 brass ( about 700ct ) I decided to just prep them all out the same including removing primer crimp even in cases that had not been crimped . I just ran every case through the swager . Sized and trimmed them all the same and started loading . Guess what ? Yep they're not all the same . I do all rifle loading on a single stage press so I load in 50rd batches . I charged 50 cases weighing each charge and when I looked at the whole lot of 50 in the loading block . I could see 7 cases were fuller then the rest . I thought that was odd so I checked there head stamp . Every one was a CBC case .
What I did then was go ahead and seat the bullets in all the cases but kept the CBC head stamped cases separate . When I got to the range I compared the CBC cases loaded at the same time with the same components to the other mixed cases . I ran the 7 CBC cases over the chrono then 7 of the other mixed brass . The CBC loads avg 115fps faster then the others .
When I got home I did a water volume test on the cases tested over the chrono . The CBC cases avg 2.3gr less volume which apparently resulted in there velocities being 115fps faster .
So can you mix brass ? Sure , but your not going to be loading very consistent cartridges . Will you notice the difference when you shoot . ? Maybe , maybe not but the fact I notice the differences when I'm loading them makes it hard for me to just keep loading what I know will be sub par ammo .
Now I don't use a progressive press and I assume guys that do would not feel and or see those differences when loading . I'd think each time the handle is pulled . The press is doing so many things . You are unable to feel the individual stations and how each may differ . I can say though when using a single stage I can see and or feel those differences . That alone plays on my mind when loading and I don't like feeling or seeing those differences .