Let me extend on that for you...

Crossbolter (crossbow gun)
3.3 bars piercing
6.6 bar speed (4 shot clip)
A weapon of wood and metal found in the ruins of the fallen kingdom Almire. Many modern gunslingers call it primitive - but it's great for shooting down just about anything.
3*

Shadowbolter
5.8 bars shadow
6.6 bars speed
A crossbow infused with shadows. It is said to have slain many a foe over the years.
4*

Sharpshooter
7.1 bars elemental
4.7 bars speed (2 shot clip)
Good chance of Knockdown on hit
Capable of shooting bolts at up to 20 metres per second, this finely crafted weapons is the pride and joy of precision aimers everywhere.
4*

Scattermaster
4.6 bars piercing
6.6 bars speed
A wild weapon that fires many shots at a time. Gunslingers find it great at clearing rooms in moments.
4*

The 4-star version branch off into different paths. The first of the Shadow path, pretty simple. Deals Shadow damage instead of Piercing. The next is the Sharpshot line. It trades clip size and direct combat abilities for longer ranged, more damaging and faster shots. It also has the ability to knock enemies down when they are hit with the weapon's projectiles, much like the second hit from a Magnus series gun. Most enemies will be affected by this knockdown, except Trojans, bosses, T2+ Alpha Wolvers and Lumbers, as well as some T3 enemies (Thwackers, etc) and enemies that are stationary (Polyps, Gun Puppies, Howlitzers). The final line is the Scatter line. It can fire between 2-4 bolts per shot. This is the opposite of the Sharpshot line, as the shots deal less damage than normal, are slower, and can act erratically, spreading in multiple directions.

Dreadnaught
6.5 bars shadow
6.6 bars speed
Low chance of causing Weak Curse
A weapons shrouded in darkness, the Dreadnaught is said to be enchanted to, when the time comes, taint it's enemies to injure themselves when they attempt to injure you.

Skullcrusher
8.4 bars elemental
4.7 bars speed
High chance of Knockdown on hit.
Favored by mercenaries and headhunters, the Skullcrusher is powerful enough to go through a line of Gun Puppies without losing speed.

Spreadspree
5.7 bars piercing
6.6 bars speed
Throws bullets around the room like a battalion of Gun Puppies. Beasts that stand in its way are known to be cut down in seconds.

The 5-star guns are better versions of their predecessors. The Dreadnaught now has a chance to cause Curse; the Cranialcrusher has a better chance of knocking down enemies; and the Spreadspree can fire 3-5 bullets instead of 2-4.

Also, the weapons have special charge attacks:

Shadowbolter/Dreadnaught: Fires a large bullet that moves moderately fast and explodes on hit, sending out four smaller bullets (two on the Shadowbolter) in random directions.

Sharpshooter/Skullcrusher: Fires a fast, powerful shot that can pierce through five enemies (three on the Sharpshooter) before phasing out.

Scattermaster/Spreadspree: Fires four waves of 3-6 bullets (two waves of 2-4 on the Scattermaster) that curve slightly toward enemies (no curving on the Scattermaster) and fade out after traveling more than 6 squares.

Firing the crossbow would be much like firing a charged shot from the Antigua. Firing the charged shot from the Spreadspree/Scattermaster would be like firing an Autogun. Firing a charged Sharpshooter/Cranialcrusher would be like firing a charged Magnus shot, with less knockback. Firing the Shadowbolter/Dreadnaught attack would be the same a the normal crossbow shot.

Thoughts on this?

"Sharpshooter
7.1 bars elemental"

"Most enemies will be affected by this knockdown, except Trojans, bosses, T2+ Alpha Wolvers and Lumbers, as well as some T3 enemies (Thwackers, Mecha Knights, etc) and enemies that are stationary (Polyps, Gun Puppies, Howlitzers)"

Excuse me, it's elemental but the knockdown cant affect the most common constructs? (lol scuttlebots/retrodes)
I'd change that.

@Alphacommando
I think Juances means the way that a Polaris shot will 'knock down' a turret - dealing enough damage to interrupt its attack. But yeah, it's not literal (lol)