Having read none of the replies, I'll add my two cents, for which you'll pay nothing :P .
First, 300gr bullets don't exactly scream "moderate loads" to me :P . If you want them so you can practice with the same weight you intend to use for hunting, that's good. But, otherwise you'll have more recoil and spend more money for nothing.
As far as down-loading goes, with faster powders that aren't position-sensitive, you can really load down. Just make sure you seat the bullet to an appropriate depth to reduce empty case volume for more consistent burns. A really light plinking load for me is a 200gr bullet seated backwards, over about 3.8gr of Unique. Quieter than .22lr from a rifle, and comes out at about 700fps (from an 8" barrel). I load the bullets backwards both so I get the wadcutter profile for easier target identification, and so I can seat the bullet deeper into the case and still get a good crimp (essentially flush, with an OAL of like 1.32" IIRC). Don't load too hot like this, though, because you'll get a lot of leading and gap blast due to the extreme "boat-tail" profile.
A more standard practice, though, would be about 6-7gr of unique behind an otherwise standard seating depth. Under a 200gr bullet seated to 1.57", it should give about 900fps (out of an 8" barrel).
And I agree that you shouldn't worry too much about it going "out of time." I've put over 1000 loads probably nearing 40k PSI through my Bull, and it's still not only perfectly timed, but lockup is tight and it hasn't become any looser in general.