For better accuracy, somthing you should look into is working up a load for your firearm !
Difrent projectiles will de-stabelise at difrent velocities, depending on barel length inchs, rifle twists, new or worn etc.
In Australia we mainly use ADI propellant.
but 308's for example, with a Sierra 150gn HPBT the load chart indicates you can use:
Min Max
----------------------------
AR2219 37.0 40.0
AR2206 43.0 45.5
AR2208 44.0 47.0
you should realy try more then one burn rate in powder but i always try the powder i use most commanly that i buy in bulk first, in this case AR2208
I just finished working up a load for my 308 i loaded 7 lots of 5 rounds with powder charges of 44, 44.5, 45, 45.5, 46, 46.5 and 47 grains i kept these together by load.
and now the easy fun part:
The rifle should already be zeroed and adjusted for windage at 100M
Place a large target up with 8 clear points to aim at like 8 small targets
you will fire 7x 5 shot groups each 5 shot group will be at difrent target
you must aim at exactly same point for each group.
Bench your firearm with a front and rear rest.
fire any 3 or more rounds to warm and foul your barel
Clean and lubricate your barel
fire first 5 44.0gn rounds at aimpoint 1
Clean and lubricate your barel
fire next 5 44.5gn rounds at aimpoint 2
do this for all 7 loads.
you will clearly notice a tightening of your group, in my case the result was
44.0gn 1
44.5gn 3/8
45.0gn 1/2
45.5gn 3/8
46.0gn 3/8
46.5gn 1
47.0gn 1 1/2 - 2 inch group at 100M
you then would repeat this test in my case concentraiting on the 45gn load.
if you were to put this load in another 308 it could shoot crap, thats why its always best to work up a load for your own gun.
why do this, A 1" Group at 100M will turn into a 2+ inch group at 200M etc..
cheers..