This mod add a powerful sniper rifle for Minecraft 1.12.2:
To craft it you need:
x1 Blaze Rod
x1 Glass Block
x1 Iron Block
And you need to craft ammo if you want to shoot.
Bullet top (bullet part 1/2):
x5 Gold Ingots
x2 Iron Ingots
Bullet bottom ( bullet part 2/2)
x5 Iron Ingots
x1 Blaze Powder
In order to craft the bullet, just put the bullet top above the bullet bottom.
This rifle deals a lot of damage, enough to one shot a large proportion of monsters.
Once you shoot, you have to wait a few seconds for the rifle to reload.
For more accuracy, you can zoom with NumPad0 (by default, you can change it in the controls, "Zoom") for 3 seconds.