I need the concept of momentum conservation in isolated systems described (in layman's terms,) as it pertains to the recoil of firearms, as described on this page. Bsharp.org : The Physics of Everyday Stuff : Gun Recoil I assume I am understanding it wrong, thinking he is saying that "while the bullet is still in the barrel" recoil doesn't happen but is "conserved" until it exits the barrel. If he isn't saying that, what is the point of Newton's first law as far as "unless acted on by an external, unbalanced force?" I don't get the "external, unbalanced" significance. I bring this up because a reoccurring claim on gun boards is that; heaver bullets impact higher than lighter bullets using the same firearm with the same point of aim. The reasoning is that heavier bullets are slower to exit the barrel so the recoil forces the barrel to rise, which results in the higher point of impact. I need a physicist to write a compelling argument as to why this is false or true. I believe it to be false but no amount of evidence I provide is considered since I'm a lowly marksman. I have some of my so called "evidence" that may be of interest? I reload ammo, and when I load develop, I use the Audette Ladder Test. It is to find where barrel vibrations are least at the muzzle as well as finding when powder charge weights reach plateaus of velocity. Since every consecutive cartridge gets a bit more powder, it hits higher than the previous one. Here is an example of one of my latest tests. There was a major vibration at the muzzle on shot #4 and the barrel whip happened to throw it higher than the next two. All other shots are true to the notion that the faster bullets impact higher; due to reaching the target sooner, therefore dropping less. Every Audette Ladder Test I have done, with snub-nose 357magnums to 26 inch barreled 30-06 rifles, at ranges from 35 yards to 400 yards, all faster bullets hit higher than slower ones. I would also add I've noticed a exception to the rule with bullets shot at just under the speed of sound hitting higher than ones shot at just above the speed of sound. A inch or so difference that I attribute to the "bullet bow shock-wave" that supersonic bullets experience. Just in case that term is unfamiliar. YouTube: Ballistic Shell Fired In Slow Motion Thank you for your time; I hope this wasn't too scatterbrained of a post.