So...not to rain on the parade here BUT, buying NEW brass does not change the equation you are already facing. If you are trying to get 'perfect fit, minimally sized' brass for load development (which is what it sounds like you are trying to do and many are encouraging you to do), then the NEW Starline brass you buy will STILL need to be fire-formed in your rifle, just like your CURRENT Lake City brass, which has been run through your sizer. So...there is nothing different with the Starline brass, other than you are 'abandoning' perfectly good, safe USED brass, for NEW perfectly good, safe brass (that will also have to be resized before first use!)
Now that we are all pretty clear on the direction you are trying to go (minimally sized brass with minimal shoulder setback), then
@milo-2 was pointing you in the right direction when he said:
And this is NOT advanced or beyond you. Go with the 'start' load in the manual, seat your bullets so they are just being held in the case, then go fire them. You will have to single load them due to their length. And as you push them into the gun and lower the bolt, you will be pushing the bullet into the case via the leade, while keeping the case pushed as far back (against the bolt face) as possible, meaning the SHOULDER will blow forward when firing, preventing any case stretch issues at the case head.
It is SAFE. It is EASY. And it will be a fun day at the range since you can work on your shooting technique and just relax as this isn't about "load development" at this point. And when you are done firing your 109 pieces of brass, they will be PERFECT for what you plan to do next (minimally size and minimally push back the shoulder so they are 'perfect' for YOUR rifle chamber.) Then you can do load development to your heart's content.
But is all this NECESSARY? No. Not at all. But some people are making it SOUND like all that was necessary, and that kind of bums me out. You can load really accurate, really safe, really good ammo without all this fussing around. Will you have to buy replacement brass a little sooner than going through all this rigamarole? Probably. But you are just getting started, so who really cares? Maybe you only get 6 firings from your brass vs 10. It's not a big deal.
Start with the basics: size per the die maker's instructions, follow the powder and/or bullet maker's reloading recipes (starting low and working up toward max), sticking with the book COAL for now, and you will have fun, make good ammo, and learn what your gun likes and doesn't like. Over time, once you have gotten your feet wet and have realized you aren't going to blow yourself and your gun up, THEN you start doing some of the more esoteric things being suggested by the ADVANCED reloaders that are on LRH. And man, there are some ADVANCED reloaders on here! And that's a good thing. For when you are ready. Because I think EVERYONE that has responded just wants to help you. We are all rooting for you. And no one wants you to feel unsafe or in danger.
Good luck with whatever you decide to do Steve.