One thing i have never understood is what the difference in bullet grains means. I have always used 150 grain in all my guns, what is the difference between 150 and 130 and so on? Why change to a different grain? Thanks for helping me understand.

Grain is a unit of weight measure. It's the weight of the projectile.

This is where physics comes into play. Weight (mass) X Speed = Energy. The weight and speed of a bullet determines it's trajectory, ability to buck wind and terminal damage upon impact. Basically what everybody refers to as "knock down power".

A 150g bullet fired at 3000 fps (muzzle) versus a 100g bullet fired at 3000 fps. The 150g bullet will travel farther, flatter, with less wind drift and usually a more devastating injury to it's intended target.

Thanks, so you are telling me that 100g would be a better bullet than 150g? If i make that change, how far off do you thing my scope will now be since the 100g has different characterestics or does it make a difference at 100yards?

No, all things being equal, the heavier 150g will be better than the 100g.

Consider the difference in damage during a collision. Would you rather be hit by a fully loaded 18 wheeler traveling 80 mph or a Yugo at 80 mph (Is that possible?)...Anyway, your chances of survival are much greater if you're hit by the smaller, lighter Yugo.

No not what he what he said, bullet grain, bullet type, and caliber, cartridge. Can not lump all 100gr bullets together, I use 168gr in my 300wm with ttsx bullets, but if I were gonna change to accubonds would use 180gr, and in my .220 swift I run 50gr but in 7/08 I run 120gr and if you change ammo little on bullet weight gun needs to be rezero'd. Just have to decide which bullet best suits your needs.

Also, other characteristics need to be considered as well. Ballistic Coefficient is basically how well or efficiently a bullet flies and cuts through the air.

A 150g. round nose will not fly as well as a 150g. boattail spire point. The higher the BC is for a given round the better it flies.

My recommendation is to not get too hung up on bullet weight. Instead, focus on a bullet TYPE that is intended for your game (i.e. varmint, deer, big bears, etc) and then find one that shoots good in your rifle. Some rifles are real picky about what they'll shoot. I have one that will group a certain 140 grain really nice while a 160 grain in the same type won't group for beans. So I use the 140's and I promise you the deer can't tell the difference between a 140 and a 160.

Thanks everyone for the help. I know NOT to change now. I was just looking for a better understanding of bullet grains and what they mean.

One "grain" is equivalent to 64.79891 Milligrams. Momentum=Mass X Velocity, Force= Mass X Acceleration, also something to remember is that a bullet's mass is also directly proportional to that amount of recoil experienced (as in, the heavier the bullet, the more felt recoil). Best way I can put it without going into a physics equation is a heavier bullet is harder to push down the barrel and, in a sense, creates more "backpressure", equating to more energy being transfered into the gun itself. In essence, this means that if you could get a big-gun (300win mag, etc) to shoot w/o recoil (sans-muzzle brake) you would experience much higher velocities (not possible, but just something to think about) due to less energy loss (same with sound - sans-supressor). Basically saying recoil, muzzle flash, sound, and heat are all wasted energy

As far as "grains" and a particular gun, typically the higher the twist-rate on the rifling (ex: 1:7 as compared to 1:10) lends itself better to stabilizing heavier grain-weight bullets. For instance, one of my .243's has a very slow-twist barrel and prefers the lighter bullets (80gr) while my other .243 has a slightly faster twist rate and is able to shoot the heavier bullets (100+ gr) much more consistantly than if i were to shoot the same load out of the slower-twist .243.

wow, sorry for the long post.

To calculate bullet energy, the velocity is squared.
The formula is E = (weight x velocity^2)/450450.

Which means increasing the speed(velocity) creates a larger increase in energy than increasing the weight(grains) by the same proportion. For example, if you just increase the speed of a bullet by 10% it will create more energy than just increasing the weight of the same bullet by 10%.

The main reason a magnum "hits harder" (on both ends) than a non mag in the same caliber is not weight/grains of the bullet but the speed of the bullet.