Thread: .308 WIN Projectile Type/Weight Advice

A lighter projectile will generally have more energy at close range (as well as less drop, drift etc) due to its velocity advantage.
A heavier projectile will generally have more energy at longer ranges (as well as less drop, drift etc). This is because the heavier projectile does a better job of retaining its velocity, so at a certain point it will overtake the lightweight fast one in terms of energy, drop, drift etc.

Penetration is determined by something called sectional density (SD). Sectional density is a measure of projectile weight vs diameter.
In simplistic terms, the heavier a projectile is for a given diameter the more it will penetrate. eg a .308 150gr and a 180gr are both the same diameter, so all else equal the 180gr will have a higher SD and therefore greater penetration.

Expansion is determined by a mixture of projectile type/construction, impact velocity, and the amount of resistance that whatever you are shooting at provides (eg a more dense target would allow greater expansion at the cost of deeper penetration).
A lighter faster bullet would generally have more "explosive expansion" (which causes a large would cavity) due to high impact velocity causing hydrostatic shock, whereas a heavier projectile would penetrate deeper, and not blow apart which will lead to deeper penetration and potentially a cleaner wound.

Basically its all a balancing act - expansion reduces penetration as it lowers the projectiles SD.
A projectile that blows apart on hit reduces penetration as the remaining parts of the projectile are not heavy enough to penetrate efficiently (the parts or heavily expanded projectile will be a large dia vs its new weight, so will have a low SD).
A projectile that does not blow apart, and retains most or all of its weight will penetrate the deepest. (weight retention / the SD does not diminish much)

Ideally you want good expansion which will make a good wound channel and cause plenty of shock effect, while retaining projectile weight (ie have it hold together and not blow apart) which will allow it to continue to penetrate deeply.
Obviously different targets require different amounts of penetration & weight retention vs expansion.

That's a bit of the technical side of it..but as others have said shooting deer with a .308 it wont matter all that much as long as you use a projectile that is intended for hunting deer sized game.