Bullet choice was easy, I have about 3k Berger 153.5s so I used Berger 153.5s
These things are going to shoot in this rifle, the thing was set up from the reamer for them.
But for your 300 PRC pick something you can get 200-400 of a matched lot of right now, something from Berger or Hornady ELD or Nosler BT or AB.
How did you choose you seat depth?
0.020" off the lands. Gotta start somewhere, it's a place to start.
In your case book COL or mag length is just as good a place to start.
How did you choose your powder range?
Powders on my list were ones commonly used in 6.5-284 Norma, it's been a benchrest standard for half of forever so there is a ton of load data floating around for it. Loaded up to what QL spit out as the max and a grain past.
In your case match up with the book data for the bullet you pick. There's tons of Berger data all over the internet, and I suggested Hornady and Nosler because they each publish up-to-date loading data for the chambering. It might not be the coolest and sexiest thing to shoot Hornady bullets, the internet might even challenge your manhood about it, but there's solid data to work off of for your first time out with the chambering.
And then after you shot you 10 shot group. How did you choose what to load further bullets in? Like how did yo narrow down form there?
After I shot the pressure strings to make sure I didn't accidentally rearrange my facial parts with any of the loads, I decided to go with more of the same powder that shot the smallest group in the ladder, H4831. I was bummed that H1000 wasn't better, but RL26 was a real disappointment. It was the fastest but at more than double the group size it's not going to work in this barrel. Speed is nice but hits are better. If H4831 decides to suck then I'll revisit H1k, then after that I'd try something new. The magical pixie dust wasn't doing it for me in this gun.
I took the fastest three charge weights that didn't show pressure signs on the brass, loaded more of them. Sat them all long at 0.020" off, I can bump them back with an arbor press at the range if I need to change the seating depth.
Don't overthink it. It's a new rifle, it'll take some time to get it in the groove
while you get you in the groove and get comfortable with what you're doing loading for it. Best bet is to load as many identical rounds early on as you can and get a real look at group size. Load as few as possible in 1gn increments from book minimum up to 1-3gn short of book max load for whatever powder/bullet combo you have, seat them to the book COL, and shoot all of them before you change anything. This will give you a basic idea of what the combo does. If it sucks completely so what, you get a firing on all the brass and some firings on the barrel and you get to shoot some. Second firing on the brass you can push up to the max, but if you start trying to max out pressure past book data then mark or trash any cases that click hard or don't eject easily. Use them for foulers but don't keep them in the rotation for load development work.
The worst thing you can do it get in a tail chase constantly changing up things too early. Cases like the 300 PRC are more forgiving that older designs, you have better case geometry to work with from the start so your shoulders stay set better and the cases don't grow nearly as fast as the old machine-gun shoulders like on the 30-06. So pick a combo, go with it, and if the rifle is worth a wooden nickel it'll shoot 5-10 shot strings under 1.25". If it does that then be happy with it and run a couple hundred through it, THEN come back as start changing things up. You might be amazed at the results you can get with book load data and factory rifle.
And don't worry about burning out the tube, you aren't anywhere in the neighborhood of doing that. Once you start cleaning the barrel with a steel brush on a cleaning rod chucked in a power drill you can start worrying about if the barrel is done. Rifles are for shooting, components are replaceable, shooting is a perishable skill set. There is no replacement for rounds sent downrange, that is the entire point of this loading exercise. Shoot more, even if it's not the perfect load.
