As stated ......grain is a measure of weight. 7000 grains equals 1 pound. Look at a ballistics program, using some velocity data gathered for different weight bullets fired from a 300 WM. This will give you a hint at expected performance from different weigh bullets, bullet drop at different ranges, bullet drift with a cross-wind at various ranges, bullet energy at various ranges, ect. The ballistics programs generally require.....muzzle velocity, bullet weight in grains, and the bullet BC. Once these values are “plugged-in”, you can get a pretty good idea of what to expect from various bullets at various ranges.
If your questions are pertaining to bullet performance on elk.....this opens up a complete new dimension as to your requirements/expectations. There is a multitude of bullet designs available to the hunter. Some cup and core bullets, by their design.....have thin jackets and open violently on impact. If these bullets are properly placed (a high shoulder shot or behind the shoulder) with minimal resistance ( not through bone heavy muscle, ect) .....they can offer a very quick clean kill. Often these bullets are offered with a very high BC, for much improved ballistics for long range shots.The negative with these bullets is that they are pretty fragile....if heavy bone is encountered, or an angled shot is required ( considerable bullet travel through bone, muscle, ect) the bullet may come apart .....and not reach the vitals. As a general statement.....cup and core bullets only have approximately 50% to 65% of their original weight retained after impact. With some of the bullets explicitly designed for long range shooting, when used at close range or encounter heavy bone ...
.there may be very little of the bullet to weigh. When a bullet sheds a high percentage of it’s weight ....penetration is severely limited.
Another school of thought is the use of mono bullets.....solid copper construction. These are required is some states, as they have no lead in them. These bullets do not expand as readily, and retain nearly 100 % of their original weight. These bullets do not “come apart” on heavy bone/muscle, or on a very close range shot.....meaning, they will penetrate much more deeply than will a cup and core bullet. These bullets require a fairly high velocity ( generally in excess of 1700 fps) at impact to achieve good expansion. This somewhat limits the range at which they offer reliable expansion. If you know what your expected maximum shot ranges will be, this is where the ballistics program can be of help.
I am a big proponent of mono bullets, as my ranges may be from several feet to 600 yards (my self-imposed range limit)! With the 300 WM, I would recommend mono’s in the 150 grains to 180 grains range. With cup and core....180 grains to around 215 grains.
This is a pretty user friendly ballistics program to use, and may help answer some of your questions. You should also do a lot of research on various bullet types from different manufacturers! memtb
http://www.shooterscalculator.com/