Don't forget that the copper is there for a reason and is beneficial. The porous bore picks up copper and smooths the micro roughness so the bullets glide thru the barrel better. If you remove it all it is going to take 5-20 shots to get back to copper equilibrium. Of course you don't want the copper layer so thick is it detrimental, but you will see that in your group size and know when to clean your barrel again.
I just ordered one of these Lee's. Got to know how they compare to my Redding Equipment. I know it's cheap but just curious how loads from this Lee will shoot compared to my other high dollar equip. May end up delegating it for pistol reloading or depriming / resizing bumping Creedmoor. Only 34.00
It's a cheap press, and does have slop in it. I have one and use a Redding S sizer, Lee neck size, and Forester seating die in it and have never noticed it creating any significant runout.
I had a buddy using one and his BTO was all over the place. Got him to try a Lee O frame single stage and his BTO is nearly perfect every time now. It’s your choice, my opinion is there are way better options available to you.
I would say Forester or any quality single stage press.
I will go against Windsage (and I'm sure most others will too) and say stay far away from a classic Lee Turret press for precision work. For high volume plinking ammo or pistol ammo go for it. The turret causes way to much slop for precision work. There, it needed to be said and I said it.
Your load is the same for all three brands of brass? Did you work up a load for each brand of brass? Each brand will have different internal volumes and therefore different pressures. My guess is the Peterson rounds are way over pressure and you’re stretching the primer pockets out.
My guess is that they shoulder bump isn’t the same on the two of them or the head spacing is slightly different so you stretch one case more than the other each firing. One could have had a new reamer used to cut the chamber and one could have been a well used reamer.
Basically in less you are setting the head spacing all the same you will likely have some differences. Maybe a dedicated set of dies or trimmer for each one would solve your problem?