Beginner's "Gotcha" #3.
Reloaders “work up “ a load by reducing book data and shooting incrementally-increasing powder loads until they reach the load specified in the book, checking for signs of pressure and that the shots stay on target. This is only half of it. To optimize a handload to the harmonics of your rifle barrel, use the following procedure:
Use bullets, cases, powder and primers you know you can get more of. No exotics or one-off sales.
Clean primer pockets with a lathe-type scraping tool like a Forstner.
Trim cases to a uniform length, whether they need it or not. Case length is not critical, just take a minimum amount off to get them uniform.
Weigh your clean, trimmed cases and segregate them into lots of plus or minus 2 grains.
Set the resizing die beginning at tallest setting by turning it down in tiny increments until the case just fits the chamber of your rifle - as tight as possible and still functions reliably.
Set the seating die to insert the bullets as tall as possible - just touching the rifling - but not so far that ejecting a loaded cartridge causes the bullet to be pulled.
Make a primerless/powderless dummy - mark with fingernail polish - and keep it with dies as your length reference to be checked with calipers. Don't fall in love with it - you may have to redo it after your powder test if it's set too long.
Reprime using match rifle primers or a conventional non-magnum primer like the Remington 9 1/2. Whatever you do, never mix primers.
Make a dozen or so test cartridges beginning with three or four grains under the maximum load listed in the book… in .2 grain increments…all the way to maximum load. Label each using a Sharpie. But watch pressure signs as you fire them.
Swab the oil from bore with Hoppes or other powder solvent followed by a dry patch - never shoot a bore with oil in it.
Shoot them at 100yds, marking and labeling each hit on a chart using your spotting scope. They will generally print low and string upward, with 3 or 4 in one, ragged hole – the powder weight in the center of that big, ragged hole is your load for that rifle.
Examine closely each case as it is ejected for flattened/blown-by primers, case stretching, and any bright ring near the case head (headspace excessive). The primers should gradually flatten until they practically melt into the case head with the hottest loads - but I don't recommend going that high - no need to and hot loads aren't as accurate.
Double check how your load resizes and seats/fires once more to make sure you are not too tight or too long.