Sniper Elite 5

You need 50 ghost kills per weapon. I found the easiest and quickest method is in mission 2.

You need non-lethal ammo for your pistol. Set starting location to CHATEAU STABLES. Then start the game.

There is a workbench in the building in South direction. ( The workbench can be used to change all weapons you have unlocked.) Pacify all enemies near the workbench. Or maybe you need to find more enemies.( 15 enemies is optimal , Because there is a ribbon Indicate you have ghost kill all 15 soldiers)

Take them to the room where the workbench located. ( For pistol, I recommend Don't stack all bodies in one place. For SMG, Stack all the body in oneplace is a better choice)

Save before you kill them all. And you can kill them all with your SMG or pistol. Then load game, repeat this progress.

This is very quick. After you have complete one gun, you can change your gun in workbench and Complete all six. It will take you less than 1h in total.

You can also use this method to complete SMG achievements.

You will need to make 50 ghost kills with each of 6 pistols in the game. Ghost kills are silent kills where the enemy you have killed has no idea who killed him. If the soldier is alerted by your presence but you manage to kill him before he alarms the others it will still count as a ghost kill. I often missed my first shot but managed to kill him after it. The best place to acquire 50 ghost kills is in the campaign. You can gradually earn ghost kills while playing this mode.

Some weapons will be locked until you unlock them in the campaign. I have listed how to unlock the pistols below as well as the required amount of ghost kills needed:

- M1911 (Unlocked from the start) - 50 Ghost kills

- Welrod (Unlocked from the start) - 50 Ghost kills

- MK VI Revolver (Complete Mission 2) - 50 Ghost kills (This one is a bit tricky because no suppressor exists for it. Instead what I did was isolate one soldier by eliminating everyone nearby. Then I would approach the isolated soldier and make a save. Finally I just continued to farm ghost kills by shooting him in the head. As long as no one can hear the gunshot it is considered a ghost kill.

- Pistole 08 (Complete Kill Challenge in Mission 3 (kill the target using a stealth takedown. Just make sure the target is unalerted when you sneak up on him and press Y)). - 50 Ghost kills

- Model D (Complete Kill Challenge in Mission 6 (kill the target using poison. Poison can be found in the ground floor where your target is on a brown table. Place it in the glass that's on top of a table with a white cloth. Let the target drink from the glass and you will unlock this weapon. You can exit out once unlocked.)) - 50 Ghost kills

- Type 14 Nambu (Complete Kill Challenge in Mission 8 (Kill the target using a Japanese weapon. You can find one on an officer or on the floor upstairs. You can knock the target out unconsciously until you acquire the nambu pistol to kill him.)) - 50 Ghost kills.

Once all 6 pistols have a gold medal you will unlock this achievement. You can check your progress in the service record bar, clicking medals, and finally weapons/items. It'll say 7/7 medals in the mastery of pistols if you have unlocked all 6 gold mastery medals. The additional medal is for getting all 6 of the pistols mastered.

Cheers! Hope this helps out

MISSION 8: RUBBLES AND RUINS
At the very beginning of the mission you will encounter 1 officer and 3 German soldiers in a small area around a fountain. Make your way to the right of the first soldier, and go into the tall grass area on his right. When the German officer says something like ‘Pack those boxes!’, make a save. Kill the officer first, then the soldier to your left that we met at the beginning, the one walking to the left and lastly the one standing in front of you in quick succession. Reload save and repeat.
Great place for tall grass kills, ghost kills, sound mask kills, 150 pistol kills and pistol masteries, just buff your pistol’s damage as much as you can and equip soft point ammo on your way to the fountain.
(Shoot the target’s body or shoot twice if you are using a low power pistol, if there’s a question mark on the soldiers when the officer’s incapacitated they still count as ghost kills as long as you are hiding in the grass)

Easiest way to get this done.

Go about getting the other achievements and leave this for last. Try to get as many ghost kills with pistols as you can while you do that.

Whatever guns you have left after doing the other achievements...

Start Mission 1

The first 3 enemies will wait for you to ghost kill them. Restart the mission and kill the same 3 enemies again. Slow, but easy.