Buy one that's preset from Timney direct.
I've purchased two of the 510 straight triggers for Rem 700s with safeties that were factory-tuned to break at a specific load and have not been disappointed. I use my rifles for precision long-range competing.
Preset is determined by personal preference and by the activity you'll be using the gun for....I like the lightest breaking trigger I can get without compromising safety...so no ultra-light breaking or hair triggers.