There are lots of classic .300 Winchester Magnum loads out there. Here are a few that I've settled on:

For testing the accuracy of a rifle, I use the following load. It has given about 1 m.o.a. (give or take) in every .300 Winchester I've tried. Velocity hovers around 3,000 f.p.s. If this load doesn't work, then you need to check your rifle or scope:

73.0 grains of IMR 4831 with any decent 180-grain bullet.

Another classic, one that seems to work in most rifles, is 75-76 grains of Reloder 22 pushing any decent 180-grain bullet. This probably gives a bit more velocity than the above IMR 4831 load, but it is widely used.

For competition shooting, the following is the longstanding classic Wimbledon Cup load for 1,000 yards:

68.5 to 69 grains of IMR 4350 pushing a Sierra 190 MK

My own 1917 Enfield (the origin of my nickname here) has a #3 contour E.R. Shaw barrel. It simply adores a mild 70.0 grains of H4831 (old or new; doesn't seem to matter) behind a 190-grain Nosler or Sierra match bullet. This only gives me about 2,840 f.p.s. velocity, but it is consistent and accurate day after day. The furthest I've shot it so far is 600 metres, but it just plain works, and I wouldn't hesitate to use it at 1,000 yards.

My main hunting load is used in my Sako L61R Finnbear. This rifle has a thin and stubby 22.5-inch barrel. It gives me better than 1 m.o.a. all the way out to 600 metres (the furthest I've shot it so far) FOR THE FIRST THREE SHOTS. After three shots, it heats up and shots start walking. It also gives me unbelievable velocity for such a short barrel:

77.5 grains Vihtavuori N560 behind a 180-grain Nosler Accubond. Velocity: 3,070 f.p.s.

The only lighter bullet load I've played with so far is as follows, but it also seems to be pretty common, from what I have read on the internet. It is also startlingly accurate, but seating depth can be tricky with lighter bullets in this cartridge because of throat lengths:

74.0 grains IMR 4350 pushing a decent 150 or 155-grain bullet.

There are so many great loads for this cartridge. I'm looking forward to playing with premium bullets in the 165 to 168-grain weight.