Yeah, the flashlight likeness is something i myself has gone away from after playing dark heresy.

Armed with a compact las pistol, i shot a guys arm, which was incinerated so fiercely that the entire torso was blackened with fire and the death throes of the poor sod makes people all around him panic.......

that was with the COMPACT las pistol.
Now imagine the las cannon! >:D

Anyway.

[quote=@Sophrus]
Personally i would have gone with a Bolt-rifle with a scope or a powerful las-gun. or something along the lines of the Vendacair rifle. 
[/quote]

Vindicare assassins rifle is known as an exitus rifle.
The ratling isn't going to get an exitus rifle. Unless he does some FANCY dealings. Since it's created and distributed by the vindicare temple themselves. For use by their own assassins.

One cool big sniper rifle in dark heresy is known as the nomad.
It has some cool story and stuff. A bit fancier and has a slight bit more punch over a regular stub sniper.
If you want something from the lore that is.

I am sure there are equivalents of a barret light .50 somewhere.

So, basically a modified heavy slug rifle firing special ammo. Nothing complex but fully well with lore.
I can bring up some dark heresy ammo types and some effects if ya like :D