Can someone explain bullet weight to me?

[Kimio]

I hear people talking about bullet weight and certain rounds having x amount of grains.

I understand Grains is a weight measurement for how much powder is in a cartridge, but how does bullet weight affect performance in a rifle' accuracy?

If I understand correctly, heavier bullets fly slower but are more accurate?

Heavier bullets also need a faster twist rate in order to stabilize them since they tend to have more powder behind them as well.

Can someone clarify this please?

 

[ROGER4314]

Grains are simply a measure of weight as ounces, gram and pounds are. There are 7000 grains to the pound and bullet weight is also measured in grains.

Your powder charge is based upon the weight of the bullet in grains. As the weight of the bullet that you select increases, the powder charge in grains of powder must decrease to keep pressure to acceptable levels.

Look at your powder charge manuals and you'll see the heavier bullet weights have lighter powder charges assuming the same powder is compared.

In general, heavier projectiles have a more curved trajectory and lower velocity. Lighter projectiles shoot a flatter trajectory and have higher velocity.

Barrel twist:
As bullets get heavier, they can't get bigger in diameter so they get longer. Heavier (longer) bullets must be spun faster to maintain stability. An AR-15 shooter using long 75-79 grain bullets may select a fast 1:7 barrel twist rate. If he decides to use 55 grain or lighter bullets, a slower 1:9 twist may be a better choice. The penalty for using a fast 1:7 twist is that barrel throat life is generally reduced.

Flash

 

[Discern]

For firearm cartridges, both the powder charge and bullet weight are measured in grains. Taking out the human factor - some barrels will be more accurate with lighter bullets while other barrels will be more accurate with heavier bullets. Taking the human factor into account, a heavier bullet will spend more time traveling down the barrel so the shooter theoretically has more time to complete the follow through. However, sometimes a heavier bullet may produce more felt recoil, and felt recoil can be a problem for some shooters. The increase in felt recoil from a cartridge with a heavier bullet is from the greater resistance of the heavier bullet not because there is more powder (should be less powder) for the load with a heavier bullet. For a shot to be accurate, the bullet needs to become stable during flight and stay stable until it hits its POA. Some elements of the equation to bullet stability are the rate of twist, bullet shape, bullet weight and speed of the bullet when it leaves the barrel.

If you are thinking about reloading, be sure to find a good mentor with a lot of actual experience. The NRA also has a reloading class that will teach you the basics. The chamber pressure of a cartridge needs to fall within a specific range (too low may have a squib which is a bullet stuck in the barrel - too high has potential to cause catastrophic damage to chamber, action, receiver, frame, barrel, shooter and spectators). Generally, if a heavier bullet is used less power is to be used. It is important to use reloading data from a respected company that is specific to the particular bullet weight, bullet manufacturer and model as not all bullets of the same weight have the same affect on the chamber pressure. You also need to use loading data specific to the powder. There are other critical aspects to reloading besides chamber pressure, so get proper training if you are considering loading your own ammo.

Those who do choose to load their own ammo are able to find a load that performs well in their firearm - if the firearm is not damaged and all other factors are done properly (stock fit, bedding, optics/sights, etc.). They can experiment and find the right power, powder charge, bullet weight, bullet manufacturer and model, etc. that works well or very well in their particular firearm.

 

[jmr40]

It is possible to shoot lighter bullets faster than heavier bullets. Generally meaning flatter trajectory. But a heavier bullet in the same caliber is longer. Everything else being equal that means more aerodnamic. At long range the more aerodynamic bullet will maintain better accuracy and energy for hunting.

The difference in trajectory is much less than many think. Using my 30-06, with my handloads as a example. I can shoot a 150 gr bullet at 3025 fps. a 180 gr bullet at only 2800 fps. By the time both bullets reach 400 yards the lighter bullet only has a 100 fps advantage, and only drops 2" less if both have a 200 yard zero. But the heavier, more aerdynamic bullet has almost 200 ft lbs more energy.

By the time you get to 700 yards the heavier bullet is actually moving faster, and is less effected by wind at any range. The biggest differnce is in the aerodynamics. All bullets have a ballistic coefficient rating. The higher the number, the more aerodynamic. The Hornady 150 gr SST's I shoot have a BC of .415, the 180's .480. Some of the better long range target bullets have a BC of over .600

 

[kraigwy]

To make it less complicated, go to your local library and find some reloading manuals.

Read the basic manuals first, then as you understand what you're reading, move to the more complicated readings.

Then move to books on ballistics.

I know I sound like a dinosaur talking about libraries in the computer age, but books are still handy and normally more accurate than internet rantings, Plus libraries are still free and there is a world of information contained on their shelves.

PS, you should see the looks from my grandkids when I mention Libraries.

Or the looks I get when I look at wind indicators and do the math in my head instead of using ipods and computers, to make adjustments

 

[big al hunter]

The only thing I see in the op that I would add to is that bullet weight is not what determines accuracy. Accuracy of a given bullet weight is a factor of twist rate. That was already mentioned, but I wanted to expound somewhat. Because twist rates determine accuracy of the bullet they also determine which bullet will or will not be likely to shoot accurately in your rifle. A perfect example of this is what happened when the 243 win. and the 6mm rem. were introduced. They were introduced at almost the same time and are ballistic twins. Same caliber bullets, nearly identical velocity. Remington expected shooters to use the 6mm for varmints which meant light bullets and a twist rate of 1/14. Winchester expected shooters to use the 243 on medium game. That meant heavier bullets and a twist rate of 1/12. Both shot very accurately with proper bullet weight. However people that owned the Remington wanted to hunt deer with the 6mm. When they shot the heavy bullets needed for deer the rifle shot horrible groups. So the 6mm got a bad reputation for accuracy. Remington changed to a 1/12 twist rate and cured the accuracy problem. So it is not always the heavier bullet that is most accurate.

 

[4EVERM-14]

kraigwy : To make it less complicated, go to your local library and find some reloading manuals.
Read the basic manuals first, then as you understand what you're reading, move to the more complicated readings.

+1

 

[SRH78]

Grains are simply a measurement of weight equal to 1/7000 of a pound. 7000 grains = 1 pound. Bullets and powder are both typically measured in grains.

Since bullet diameter for a given caliber is fixed, bullet length varies with the weight of the bullet and also the shape. Longer bullets need to be spun faster to be stable than shorter ones. Each bullet has an ideal twist rate. If you spin it too slow, it wont stabilize. If you spin it excessively fast, accuracy will suffer.

All else being equal, heavier bullets use less powder. The reason is pressure. A heavier bullet provides more resistance because of the increased weight and the increased bearing surface. Bearing surface is the portion of the bullet actually in contact with the barrel. Because of this, the same amount of powder behind a heavier bullet produces more pressure so you must reduce the amount of powder with heavier bullets.