First congrats on your new rig! We have sold quite a few of the FCP's and BA's and they all seem to be from very good to great shooters
There are many different approaches to breaking in a new rifle and a lot of vodoo also - but I can only give you my usual approach.
Usually- I start out by using a bit of JB cleaning compound or another mild abbrasive to even out some of the tool marks in the barrel. Use a quality cleaning rod, a bore guide and short stroke a tighly fitted patch on a jag.
Many prefer a shoot clean way like suggested by for instance Shilen. If you go to their webiste there is a good explanation there.
After having taken out some of the tool marks with JB THOROUGHLY clean your barrels with regular solvent. On the same jag with new patch.
Now you barrels should be a little smoother and ready for the range. But before going to the range you need some cartridges.
I usually do quite a bit of exploring on a new barrel and chamber before starting to reload. If you do not have a trying case like Hornady offers - load one up and dump one shot in the ground behind your house if you live in rural surroundings.
This case is now ready to test your different bullets to determine MAX OAL for each bullet in your
chamber. Without knowing your exact chamber it will prove very difficult to determine optimum seating depth for your bullets.
Your now newly fired case is the basis for your testing.
- Size only a very small portion of your case neck. Just enough to hold your bullet. 0.2-0,3mm is enough
- Now seat your bullet of choice barrely in the case mouth, just enought to get the bearing surface of that bullet into the case mouth.
- Place this very long cartridge into your chamber, and slowly close the bolt behind it
- When your bullet hits the lands it will be pushed down into your case - creating a cartridge of maximum lenght in your chamber, with this exact bullet.
- Measure and mark down the max lenght of your cartridges with this bullet in your relading log.
- Repeat 1 thru 4 a couple of more times to verify that the measure you got is correct.
If performed correctly your can find measures for all the bullets you will like to try this way. A common mistake is sizing the case mouth to little or too much. Too little and the bullet slides out when being extracted, too much pushes the bullet into the lands and gets stuck. You can easily retrive it by carefully pushing it out with your cleaning rod.
Since you now have measures you can use for your COAL you can look at loading recipies that others have had succes with. Usually you will find if they let bullets jump(being of the lands) usually marked with a -.XX" or being jammed marked by +.00". Which means you force the bullet a little into lands to create a more uniform pressure build up.
Your bullet of choice usually will not fit your magazine seated to touch or into the lands.But measure and find out. 300 Berger OTM's are one of the most precise bullets available and you should have llittle problems finding a load that shoots.
When finding pressure I usually find a reputable loading manual either in paper or online.
Hornady's newest is a very good one. Online Hodgdon's load data is unsurpassed!
If you do not have a chono and a micrometer - purchase both. Learn how to determine pressure by meassuring case head expansion. By monitoring the case heads you make sure you will never load cartridges with dangerous pressure.
Load 5 cartridges with 0,5 grs increments from 2-4% below max loads in the manual of choice, if you have more than one its allways better. Shoot them over a chrono - log speed, case head expantion, and last but not least how they group. Start by letting bullets jump approx .20".
After having determined your max pressure you can start thinkering with seating depth. Load a minimum of 3 - 3 shot groups with each lenght. At the same time shot them over a chrono. Seathing depth often changes both speed and ES/SD of your load. If you are not familiar with those terms look them up. The lower figures you get the less vertical groups are you getting. A faster bullets shoots quite a bit higher than one travelling only marginally slower when reaching far out there.
Warning - To not use max loads trying to jam bullets into the lands. Excessive pressure may be the result.
After this you need a decent balistics program, a good log book were you record how your load shoots in different conditions. You are most likely going to buy yourself a portable weather station. I can recommend a Kerstrell 2500 as a good introductory unit. It works well and give you most of the data you will need. Altitude you can get from a map, barometric pressure, temperature, wind speed is the essentials.
Now learn about wind deflection of bullets and last but not least shoot in as many different conditions as possible. Always be 100% concentrated when trying to shoot LR. Practicing perfection makes perfect - not just practice.
We have have great results with 88-90grs of RE 25 behind both Berger 300 and Scenar 300's in our 338 LM. But if you already have H-1000 avaiable use it - as the Re 25 load is a bit more temperature sensitive than the H powder
Hope this helped you out a bit for starters. Good shooting.