There is tons of information available for reloading .338 LM out there. Here’s a sticky thread on SH:
pyrofx XSergeant Rating: 3.0/5 this site 388 posts this site >338 Lapua Magnum 10/08/2014 (1 vote) Just tried the reloader 33 powder in the 338 . 99.0 gr Kreiger 9.3 x27 fed 215mag hornydaddy 285 2789 es of 6 with hornydaddy brass. bolt lifts fine untill the cam over . then it takes a bit of...
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If you want someone to tell the perfect load for your specific rifle, then you may be waiting a while. Buy some 250, 285, and 300 grain loads and see what your rifle likes. If reloading, you have to do the work, like everyone else. Look through the various loads posted, get an idea of where you want to start, and what bullet weight you prefer, using H1000 or Retumbo, measure where your lands are and start about 0.020” off the lands.
Then just do it.
If you have a specific purpose for this rifle or preferred bullet you want to use, post it up and then those that actually have experience with that bullet may be able to assist.