TLDR; Buy Mosin Sniper from Praps, Carbine Sniper Stock from Jaeger, Wilston Cigs from Flea and do Mechanic's Obrez Trade. Then turn your original 730m Mosin Sniper into a 514m Mosin Sniper Carbine by purchasing the necessary parts from Jaeger. Now you have two Mosin's for only a little more than the price of one.
Tarkov Shooter can be a very painful quest, but I think it is less painful to actually carry out for a newer player than some of his other quests (e.g. Secured Perimeter, Tremor Headshots, Survivalist Path Tough Guy are hard if you aren't a good shot and good at Woods).
What makes Tarkov Shooter so painful is that Mosin's cost a god damn fortune.
The Mosin is one of a select few guns in the game that generally costs more at the Flea Market than from Prapor. This is likely because of the combination of the demand created by players attempting to complete this weapon restricted questline and the lowered supply from how large the Mosin itself is, making lugging an FIR one off the map a low priority endeavor for many players and thus lowering demand.
To help ease some of this pain, I will show you how to get Mosin's for slightly cheaper.
Requirements: Prapor LL2, Mechanic LL2, Jaeger LL2, Unlocked Flea Market
(Until you have these I would recommend primarily using Mosins that you find off scavs and not trying to advance past Tarkov Shooter 3, as Tarkov 4 with short range PMC kills can cost a fortune)
- Purchase Mosin Sniper from Prapor (which has a 730mm Mosin Barrel and Regular Mosin Rifle Stock)
- Purchase 2x Mosin Carbine Sniper Stock from Jaeger
- Purchase Wilston Cigarettes from Flea Market
- Trade 730mm Mosin Barrel*, 1x Mosin Carbine Sniper Stock and Wilston's to Mechanic for a Mosin Obrez
- Purchase 514 mm Mosin Barrel from Jaeger
- You will have a non-operational Mosin in your inventory now with just a Regular Mosin Rifle Stock on it
- Modify the above non-operational Mosin by replacing the Rifle Stock with the Carbine Sniper Stock and then put the 514mm Barrel on it
- Sell the Regular Mosin Rifle Stock its not useful to you any more
*This trade will automatically pull the barrel off of the Mosin Sniper you bought from Prapor
Result: You have 1 Mosin Obrez and 1 Mosin Sniper Carbine for the cost of:
52k Mosin Sniper + 7k for 2 Carbine Sniper Stocks + ~6k Cigarettes + 4k 514mm Barrel – 3k Sold Regular Rifle Stock = ~67k Roubles or 33k per Mosin
If I'm using a sniper rifle don't I want to use the long 730mm Mosin Barrel?
Your mileage may vary but in my opinion the Mosin is a definite example of "It's not about the size but how you use it".
Since the Mosin is a bolt action, I don't believe recoil affects performance whatsoever. You will have to re-ADS every time you shoot.
Using the longer barrel and the accompanying regular rifle stock gives you a +5.4 Muzzle velocity at the cost of -18 Ergonomics compared to the Carbine Sniper version (514mm and accompanying Carbine Sniper Stock).
Since Ergonomics governs how quickly you ADS and how long you can ADS before your PMC's arms get tired, I believe that this trade off is well worth it.
Perhaps a highly skilled player will notice the difference in muzzle velocity when sniping from 150mm+, but I think every player will notice the -18 ergonomics difference when trying to do anything with the gun.
What if I don't like the Mosin Obrez?
While I'd minimally recommend holding onto these bad boys and spamming them on Factory with a blue laser to complete Tarkov Shooter 4 (short range PMC kills), you are free to sell the Tri-Rail, Sawed off Sniper Stock and 214mm Barrel and replace them with the 514mm barrel and Sniper Carbine Stock.
The net impact of swapping from Mosin Obrez to Mosin Sniper Carbine will be less than 5k Roubles, but again I like the Obrez and have no issues shooting PMCs under 50m or Scavs at any range with it.
What kind of bullets should I put in my Mosin?
In my opinion when you are working on this quest you should always run 7N1 (thorax ammo). Even if you have to buy it at the Flea Market price, you're going to be spending most of your time shooting scavs and lightly geared players and being able to confidently one tap them in the chest will make a major quality of life difference.
If you are good enough at headshots that you are hitting them consistently then feel free to use the cheaper SNB or the even higher penetration 7N37 but you probably didn't need me to tell you that.
What map should I run my Mosin on?
As I mentioned above, bringing your Obrezes to factory is the easiest (relatively) way to get Tarkov Shooter 4 completed. For Tarkov Shooter 8 you have no choice but to go to Woods.
For the rest except Tarkov Shooter 7, which allow you to shoot Scavs, I believe that Customs is the easiest because it has the highest concentration of Sniper Scavs, which are basically sitting ducks for your Mosin.
Once you've dispatched of nearby Sniper Scavs, the Scav spawns in Old and New Gas Station as well as the Military Checkpoint are pretty easy to farm for Mosin kills from over 40/55/60 meters away depending on the quest.
Tarkov Shooter 7 requires you to kill PMCs with suppressed Mosin over 55 meters, and I would recommend Woods for this if you want to do it honorably, or Interchange/Shoreline if you're desperate enough to finish the quest that you are willing to Exfil Camp.
As a note, the stock Mosin suppressor, the Bramit, costs ~30k but you will also have access to the Tiger Rock Mosin thread adapter which (with another adapter on top) will also allow you to use various Kalashnikov and NATO adapters. The cost ends up about the same at 30k but it took me a little while to realize that I had other options than just the Bramit which sometimes can get up to 40k since people spam purchase them for these very quests.
What if I hate the Mosin?
Well if you don't already, trying to complete all 8 of these quests will certainly make you.
My recommendation for all but Tarkov Shooter 4, 7 and 8, which I addressed above, would be to run a loadout you are comfortable with using and losing plus a 2x scoped Mosin Sniper Carbine on your back.
Find Scav spawns, if they harass you shoot them in the legs with your primary weapon so they leave you alone and stop moving around so much, then put 50m between you, switch to your trusty Nagant and rain holy 7N1 vengeance upon them.
I hope this helps.