What is grain and how is it used in firearm ammunition? Grain is just a unit of measurement for weight. There are two 7.62×39 ammo for sale common uses for this unit of measurement in ammunition. First is the weight of the bullet and second is the amount of powder, by weight, used in the cartridge.
If you’re buying ammunition from a supplier the only use of grain typically advertised by most manufacturers is the weight of the bullet, or the part of the cartridge that is propelled through the firearm when the powder is ignited. You should see a cartridge description on the side of most boxes of ammo that will look like this; “30-06 Springfield, 180 Gr. FMJBT.” This tells you that the 30-06 cartridges are loaded with bullets that weigh 180 grains and the rest describes the other characteristics of the bullet as a “Full Metal Jacket Boat Tail.” An easy way to think about it is to imagine grain as a grain of sand and that it takes 437.5 grains of sand to equal one ounce. So your 180 grain bullet weighs about four tenths of an ounce.
Why do I care what the bullet weighs? That is a good question. You might think that as long as I have the right caliber ammunition the bullet weight doesn’t matter. But it actually does matter. It’s not difficult to figure out why it matters if you just think about it in terms of things you deal with on a daily basis. If you want to make it difficult you could study physics and the principles of mass and momentum but you’ll have to find someone smarter than me to teach it to you. So let’s keep it simple.
Weight matters because it’s directly related to the amount of force it delivers on impact. The easy way to demonstrate this is to imagine you want to sell something and you want to put a sign in your front yard. So you take a wooden stake and you have two hammers, one small tack hammer and one big sledge hammer. First you take the tack hammer and after a dozen times hitting the stack you realize it is just to slow so you grab the sledge hammer and with one good hit the stack is in and you’re done. You learn from this that the heavier the hammer the more force it delivers on impact. This is the same with a bullet in that the heavier the bullet the more force it delivers on impact. Remember this article is about keeping it simple so if you’re thinking about the forces of gravity, friction and distance you’re way ahead of me.
Back to the hammer example the other thing you would have learned is that even though the sledge hammer delivered much more energy it also took a lot more energy to lift it. That is where the other measurement of grain comes in. You won’t need to know this unless you start doing your own ammunition loading but just to get you familiar with grain the other use is in the amount of powder used in the cartridge. When you lifted the tack hammer it was very easy and like in ammo a lighter bullet can be propelled with a lighter amount of powder and the more energy it took to lift the sledge is similar to the more amount of powder is required to propel the heavier bullet. So for the purposes of this article there are two uses for grain and one is the weight of the bullet and the other is the amount of powder in weight it takes to propel the bullet. There are many different types of powder used in ammunition and each has different properties but regardless which powder is used the amount is measured by weight in grains.
One last thing is that I don’t want to give the impression that a heavier bullet is always better. There are numerous applications where a lighter bullet is more favorable. The.338 Lapua Magnum is a perfect example. When this cartridge was developed it was based on the military needs for an accurate long range rifle. To make a long story short in the end the developer took a.416 cartridge and narrowed the necked to fit a.338 giving them a.416 powder charge with a.338 bullet. The result was a lighter bullet propelled by the powder of the heavier.416 cartridge. The lighter bullet gave them greater muzzle velocities, longer range and still delivered the required force on impact over the required long distance. The phrases “Sabot round” or “Necked Down” are describing ammunition designed to use lighter bullets. You can do your own comparisons next time you go to buy ammunition for your firearms. Look at all the different loads available for your gun and compare the muzzle velocities and force over distance. You may find that some weights will work well for you for some of your targets and others that will work better for other targets.