Hitman HD Pack

After completing the mission with the firearm you have save and start he next level. You can quit to the title screen and select Continue on the menu to receive a full list of selectable missions. Just remember to complete it on your most current save as not to get shorted any firearms. Also DO NOT take weapons into levels and leave them, otherwise they are GONE. Then you'll have to recover them or be rewarded them again.

For the most part once your gain and finish the mission with the missing weapon, the achievement will pop right as your saving and changing to the next level. This saves you from having to go into the training room just to verify. Here is my list currently of sniper rifles and I'm also providing levels where certain firearms can be found:

1 - Enforcer Sniper
*Asylum Aftermath (gun cabinet upstairs by the circular staircase)
*Beldingford Manor
*Lee Hong Assassination

2 - Dragunov Sniper
*Asylum Aftermath (carried by police standing by their cars at the gates)
*The Meat King's Party
*The Bjarkhov Bomb
*Rendevouz in Rotterdam
*Slaying a Dragon

3 - R93 Sniper
*Deadly Cargo (very far corner warehouse roof, accessed via a inside ladder)
*The Seafood Massacre

4 - W2000 Sniper
*Traditions of the Trade
*Slaying a Dragon (standard equipment in suitcase, just take it with you)
*The Wang Fou Incident
*The Seafood Massacre
*Lee Hong Assassination
*Hunter and Hunted

5 - PGM Sniper
*Hunter and Hunted (rooftop sniper can drop it upon death to the street)

As for the PGM Sniper, this is by far the most difficult weapon to gain. On the last level, Hunter and Hunted, outside the buildings across the street, highlighted by blue neon lights, there is a lone SWAT sniper across on the rooftop. I tried my best to develop a surefire way to get the rifle and came up with a combination of scenarios that work, but are not 100% and are very treacherous. The main flaws in each way is that you can't predict enemy movement, and if you are working a weapon completion on Professional difficulty like I did, it is just damn hard. What I ended up doing was selecting silenced weapons and guns from the first level I could easily go back and get. I tried several times (hours) and decided this was the fastest way for me to just get business done.

On each instance, from the point you start the level the police are outside at the second floor landing coming up to the third. I took an AUG rifle and exited the room via the white doors on the right and quickly took aim at the sniper. He is just to the right and across the street. Once you fire on him, he'll take aim, and drop the rifle upon dieing. I would always make sure I could see the rifle drop to the street below. (Even turning up the brightness on my TV because there isn't time to waste in this level). As soon as that is done you can VERY FAST run out of the room, and straight ahead taking the first room on the right. If you're spotted, that is ok, because the only glitch to this level is that 80% of the time as soon as you cross the balcony or enter into the animation, the police won't shoot you. This helps two ways. In one way you can just leave, re-enter the hotel, hit the lights and slip downstairs. In another way, you can kill the police, cross over, take a uniform, then cross back the same way to turn the lights off and escape.

The only downside to all of this is that I found on the streets the guards might randomly blow your disguise, or when you pick-up the rifle, you blow your disguise. I have no idea why sometimes it does and sometimes it doesn't. You could try to pick them off one by one from a distance, just make sure you equip every concealable silenced weapon you can. On my final run, I took the mini gun and just mowed everyone down. I did my little aim out the window and took the sniper out with my pistols, picked up the mini gun, taunted the guards down the hall, and then just held back and gunned everyone coming through the door down. At one point, I took a disguise, this might give a split second life saver when they come in the door. The mini-gun causes more smoke and flashes so it gets a little tense. After everyone is gone, there will be just a few officers roaming the lower halls, in the alley, and on the street corners. Take them from a distance, grab the rifle, take out the target, and run like hell.

This achievement requires you to unlock five sniper rifles. Before I list them, please be aware of the following things:

* You do not have to unlock the crossbow (for this achievement, or for any of the other achievements)

* Be aware that if you take a weapon on a mission, even if you have already unlocked it, you will lose it if you drop it in a mission. For example, I had the SVD unlocked, took it with me on one of the Japanese missions and dropped it mid-mission. It was removed from my shed and I had to unlock it again.

R93 sniper
Anathema

This is located inside the garage with the red escape car you use to exit the level.

SVD rifle
Kirov Park Meeting

Immediately in front of you when you get out of the boat, go up the stairs and you will notice some green dumpsters. The SVD is behind the dumpsters. You exit this level via the boat you arrived, so you can pick the sniper up just as you are about to finish the level. Just watch the guard who patrols the path - he doesn't like you being near the dumpsters.

M195 rifle
Motorcade Interception

Simple to find, you get it from your contact.. however, not so easy to escape with. The best method for me was to begin by killing all the guards in the area around the rifle and around the exit - just go to town and kill everybody in these areas. Then, grab the rifle and climb up the ladder to trigger the motorcade. Don't snipe from up on the roof - I found this to be a bad position. Instead, head back down to the ground and snipe the target from there. Then you can easily make a run for the exit with the gun.

W2000
St. Petersberg Revisited
This was straight forward for me - I did this on my first and only play through of this mission. You will find it in the room with Agent 17.

Custom Rifle (W2000)
At the Gates
One of the harder snipers to get, but follow this method:

1) Take the R93 sniper with you (you will lose it using this method, but this is very easy to unlock again) and a silenced pistol.

2) From the start, run right up onto the ledge and keep going. You will find a lone guard patrolling along here. Snipe him and take his clothes. Keep to the right here and move onwards. Stop when you are level with the sniper tower on your left.

3) Crouch and aim at the sniper up in the left window of the tower. Shoot him once in the small amount of leg he has exposed. This should not kill him. He will then aim at you. When he aims at you, kill him quickly -- hopefully, his sniper will have dropped out the window, slid down the roof, and landed on the ground. Pick it up and continue as normal.

This sniper is a pain, but this method works well. I have done it multiple times on the hardest difficulty, and if it doesn't work it, is very easy to retry because you only have one enemy to kill if you retry. You can get this sniper on the final mission too, but I found this a nightmare to accomplish because of the boss.. but try it out by all means.

Good luck weapon hunters!