Well, the simple answer to both is a heavier bb.

Now for those of you that shoot .20's, you say...but a .20g bb has a higher muzzle velocity then a .25g bb. It's on average ~50fps higher. To those of you that say that...I say, you are absolutely, positively correct!

But, at 10 yards, I'll say the .20g bb will be traveling as fast as the .25g bb. But, you ask...how can this be?!

Well...its a physical principle called Inertia!

Inertia -

*Physics*- The tendency of a body to resist acceleration; the tendency of a body at rest to remain at rest or of a body in straight line motion to stay in motion in a straight line unless acted on by an outside force.

And the last example is an airsoft bb.

Which ties into Newton's Three Laws of Motion:

Newton's laws of motion

The three laws proposed by Sir Isaac Newton concerning relations between force, motion, acceleration, mass, and inertia. These laws form the basis of classical mechanics and were elemental in solidifying the concepts of force, mass, and inertia.

Newton's first law states that a body at rest will remain at rest, and a body in motion will remain in motion with a constant velocity, unless acted upon by a force. This law is also called the law of inertia.

Newton's second law states that a force acting on a body is equal to the acceleration of that body times its mass. Expressed mathematically, F = ma, where F is the force in Newtons, m is the mass of the body in kilograms, and a is the acceleration in meters per second per second.

Newton's third law states that for every action there is an equal and opposite reaction. Thus, if one body exerts a force F on a second body, the first body also undergoes a force of the same strength but in the opposite direction. This law lies behind the design of rocket propulsion, in which matter forced out of a burner at high speeds creates an equal force driving the rocket forward.

And the key here is MASS, the heavier the bb...the more air resistance it take to slow it down. Thus while the .25g bb leaves the barrel slower then the .20g bb. The .25g bb will travel further because its mass is higher and it takes longer for air resistance to slow it down.

Now, I am about to give you a real life example.

If you take a pitcher in baseball and you hand him a baseball. He winds up and with his perfect motion he throws a 100 mph fastball. He does this over and over again and just hits strikes. Plain, simple for strike fast balls. The baseball leaves his hand at about 102mph and hits the catchers glove at about 100mph.

Now, take away that baseball and give him a whiffle ball the size of a baseball and have him throw it with the same perfect motion he uses for baseballs. How many of you can already see whats going to happen? His velocity is not going to be 100mph at the catchers glove. The whiffle ball may even leave the pitchers hand at 125 mph, but at 60 feet what his velocity? 40 mph, 30 mph, 20 mph? How many will say it may not even make it to the plate, except maybe on a bounce or two? How is his accuracy? Pretty bad, no?

Well the "same" thing happens in airsoft. Lighter bb's have worse range and worse accuracy.

So...shoot a heavier bb for better range and accuracy!

Questions?