In the old days, you could find several pros that used actual full-auto guns like sniper rifles. Strate up, across-the-map shootouts, all with autos of some sort. Even against people who primarily used snipers.
For a long time, I have been using L115A3 & CPW. I have gotten so good I can use the CPW as a 'backup' sniper after using it for a while. When I got tired of using the shotgun(also used pretty heavily), I started using UMP, then used it snipe as well; (because of the gun's stats, the UMP and CPW are practically the same guns when in use). Then went up to blast gun*refunded*, GA3A [used as a sniper]*refunded 3x times*(ga3a is just a pitiful rifle in-game), carbine [was an even better gun & sniper, but it shoots slowly] *refunded* and now I'm on G36.
The G36 is not a trash gun like the (cough 'GA3A' cough). But I'm still getting used to it. The sniping potential is the same if not better than the GA3A, but the use is different. If you are like me, you also like autos you can snipe with, then the G36 is good. But the G36, unlike the GA3A, has a scope. Use the red dot scope for short-range; I know it has a big red dot, but it will feel like it shoots straiter using the red dot at short distances. Use the red dot for full auto shooting(scoping in removes the bullet spread) and try not to hip-fire the rifle. Now for long distances, if you use the usual tricks, it snipes great.
Now, if you don't know what I'm talking about or how to use full-auto guns as a sniper, that's ok big Z will tell you the tricks.
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If you have done that, then you are all set for the needed options.
Depending on the gun, it will work differently because of the options you just picked(Enable iron sights: False). If it had an iron sight, it won't now(obviously). Right-click will now do a kind of third-person view zoom. Similar to "scoping in" on snipers minus the scope, it will now also have an aiming dot (Crosshair dot: True). The aiming-dot is better for head & body shots, but leading shots may be more difficult now. But to shoot and hit things accurately, an aim-dot is needed (more or less).
When shooting, you should single tap or do 2 round bursts For long-range with full-auto guns. Don't hold it down if your sniping. Also, you want to practice excellent trigger discipline. If you don't waste ammo more than you have to, you will live longer and win more.
With that, any auto gun/rifle is not a replacement for a sniper rifle. The only gun that could be 'argued' as technically a replacement, or gun to use other than a sniper rifle, is the revolver. {That is if you disregard the Pulse Pistol because of its low damage comparatively. Then you don't count the CPW as it's full auto. Then finally does not count the WarBow, because it's a bow, not a gun. Even if the Warbow is the actual sniper "replacement" for your secondary weapon slot}; Additionally, you can use the sniper-like it's a shotgun, but it's not good for that. (L115A3, no / Rail Rifle, yes).
I wrote this kind of as a question and an answer, Are there any auto snipers left from the old days? And Yes you can legitimately snipe With autos, no that's not cap. I will even tell you how to do it.