There are 12 Vietnam Weapons that you must get a gold star in. To get a gold star in a weapon you must get 100 kills with that weapon. Don’t start one weapon and not finish or move onto another weapon. Work your way through, kit by kit. For a sniper rifle, play rush. Camp behind the battlefield. Pick off people by scanning the horizon/battle area with your scope (for most sniper rifles use the 12x scope). Most guns need to be used in close quarter combat to be good. It would be a lot easier if they had a red dot sight or 4x sight like in the original games online mode.
List of primary weapons that are needed:
M16A1(Assault kit) This is not a good gun. It's one of the worst assault rifles. Use the Marksman Assault Rifle Training Specialization to help with this guns poor accuracy.
AK47 (Assault kit) Easy gun to get kills with. Shouldn’t be too much of a problem.
M14 (Assault kit) This isn't a good gun. Only good at close range. Needs a lot of reloading. Magnum bullets are an option for this gun and are needed, so use them!
M60 (Medic kit) the M60’s big magazine count makes this a briliant gun. It's heavy therefore decreases sprinting speed, but shouldn’t be a problem.
RPK (Medic kit) My personal favourite. Like the m60, has a pretty large magazine count. Easy to get kills with. Take out pockets of enemies with this with one magazine.
XM22 (Medic kit) Much like the M249 SAW, easy gun to get kills with. Has a large magazine count. Use the Marksman LMG training specialization to help keep the gun steady.
M10 (Engineer kit) Good gun. Use it in small bursts at close range. Really good for protecting objectives.
PPSh (Engineer kit) One of the best SMG’s in the DLC. Has a low recoil and brilliant fire power.
UZI (Engineer kit) Better firepower than the m10, but less accuracy. I recommend using the Marksman SMG Training Specialization. Also, if you want you can use the ammo upgrade to help with its rate of fire.
M21 (Recon kit) One of the worst snipers. You need at least 3 well placed shots to kill someone, and that’s when you use magnum ammo. Use it at closer range than other sniper rifles.
SVD (Recon kit)Slightly better than the m21. Use its 12x scope which is the best scope in the DLC. When using the 12x scope, you can snipe from medium to long distances.
M40 (Recon kit) Use magnum bullets with this gun for one-shot-one kill, also use the 12x scope.