Picked up a new 7prc this weekend. Bought several boxes of factory to initially run through the gun. How many rounds do you run through a new gun before starting to find that guns load?

I start right away. Clean it and get to load development. A few fowlers and go.

I had a factory Tikka that shot absolutely horrible until it hit about 30 rounds. It’s the only time that’s happened to me, but it shows it’s possible.

Depends. Competition or just hunting. If just hunting I would sight in with factory 10-15 rounds let’s say. Then clean and start loading to a velocity/ accuracy point I was happy with.
Reloder 26 is the velocity champion on that cartridge but hard to find. H1000 and H 4831 shoot great if that helps.

Check torque on all the screws.
Verify the barrel is free floated, correct that if not.
Find the lands with a modified piece of brass.
Load the bullet .005" jump, if that will fit in the magazine.
Make 3 rounds of my start charge, shoot those at 100 yards.
Repeat that two more times, and get the scope/rifle/load zeroed at 100 yards.
Take the start charge to 200 yards and shoot that.
Climb in powder charge, in increments.
The winning powder charge is recreated, and zeroed at 100 yards again.
Go get DOPE to 800 yards.

Sight in with around 15 rounds and start.

I started new 7 PRC hunting rifle for a guy on Sunday. Fed Premium with 175 ELDX, sight in with two rounds, shoot one more and clean. Shot 11 more and cleaned. Shot a 12 shot ladder with Berger 175 EOL's and found what I was looking for. Will fine tune today.

Side Note- The Federal Premium with the 175 ELDX shot very very good in this rifle, the ES was 51 over 14 shots, not great, but grouped really nice at 200 yds during the break in.

I've developed loads for 8 different rifles in 7 PRC the last 8 months. Each time with ADG brass or Peterson brass. CCI-250 or Fed-215. H-1000 in every rifle. Berger 175 or Hornady 175 ELD-X.

What I've seen is it behaves similar to the 6.5 Creedmoor. The winning powder charges for each rifle are close to each other, or identical. I don't have to test a wide array of powder charges. The node seems to be easy to find from one rifle to the next. Look at the case geometry of the Creedmoor and the 7 PRC. You can see they are very similar, albeit the 7 PRC is a larger cartridge, of course.

LSCobra, TCB which rifles are you talking about?

Great information gents!!!!

Buzz...I grabbed a Savage Trail Hunter Lite.....20" threaded with fluted barrel.

Verify the barrel is free floated when the barrel is hot as well. I chased my tail on a rifle for way too long.

When I free float one, I give it quite a bit more clearance than the factory does. For the reason you mentioned.

It might look like I went too far, to some people. But, I'm function over fashion. What good is a nice looking rifle that doesn't shoot straight?

This particular one is an AntiX, Proof Carbon, Manners PH that I built for a client.

It's been a few years now, but I went all OCD on my last new rifle purchase (Tikka, chrome moly barrel, chambered for .300WSM), doing a barrel break-in with 10 rounds of clean-and-shoot, followed by cleaning after every 3rd. That pretty much got me through the first box of factory ammunition, got my scope more or less zeroed, and gave me some once-fired brass to start load development.

Maybe the break-in was unnecessary, and maybe (probably) I was just really lucky with this particular rifle, but it shot beautiful cloverleafs (using Sierra 168 gr Match Kings) with every powder charge (RL-19) from middling up to maximum!

If I were you (whether you agree with a barrel break-in procedure or not), I believe I'd begin load development just as soon as I had enough once-fired brass to get started. 15 ought to be enough, if trying out just a single powder.

I like 50-100 round, before doing final load work up.

Unnecessary

I clean the barrel good and shoot it 5-10 times to foul the barrel and sight it in. Then I start load development. Often shoot 30 or so during load development. IF I find a load I like, I load the remaining 10-15 out of the batch of 50 cases I have been working out of and shoot them for groups at various distances to confirm how the load shoots and complete fire forming that batch of 50 cases.
So, I get started right away.