This weapon was added in the Betrayal DLC for Hardline. You may better know this weapon as the Springfield, which is a bolt action rifle. Just like every other WWI and WWII weapon that Visceral adds to Hardline, this weapon has little to no attachments. The weapon is classified under the "Sniper Rifle" section of the gun selection screen, and can be equipped as any of the 4 classes. The only 2 attachments you can add to the weapon is a 6x hunter scope and a silencer.
This weapon is a real pain to use. I have tested to see what the damage output is like. If the person you shot had 100% health before you shot them, the maximum damage the Springfield does is 75% if hit in the torso, which, on the positive side, is just enough to get you an assist counts as kill. Of course a headshot, however, is an instant kill. It is very hard to get a kill with this weapon in the sense that although the weapon allows you to shoot relatively quickly, compared to other players who are likely using the vast amount of automatic weapons in the game, it is hard to follow up on a kill.
After using the weapon for awhile you might feel that it is very frustrating to try and get a consistent amount of kills with the weapon. If you do feel this way, as I did, hardcore mode is an option. In hardcore mode everybody is basically a one shot kill, although your HUD is missing and its hard to find people. There are always Hardcore servers that are populated, especially in Blood Money. So if you find that the weapon is just not working out in regular, there is a slower but less frustrating way to get the kills. I say slower because without a radar and without the after death cam, its hard to really judge where anybody is on the map.
The first Gold star for a weapon requires that you have to get 275 kills with a weapon, so that is how many kills with the Springfield that is required for this achievement.
If there are any questions or concerns please let me know in the comments.