Some of the changes we know:
i. Shooting were done one weapon type at a time;
ii. Jink has to be declared before any To Hit rolls were made;
iii. Casualty is measured using the maximum range of the weapon.
Say I have 5 Marines rapid firing a 10 man Ork Boyz. Out of that number, only 5 Orks are within rapid fire range.
In 6th: maximum casualty is 5 Orks due to 12 inches Rapid Fire range.
But in 7th: the casualty can go up to maximum range of the bolter (24 inches) even if all 5 marines Rapid Fired. So if I'm lucky, I might even kill the whole 10 man Boyz.
iv. Units that go to ground or is pinned cannot Overwatch though they can Snap Fire.
v. Scatter dice and 2D6 must be rolled together. Last time rolled scatter dice first, then rolled 2D6 only if arrow is up.