Rifles

Personally, I would recommend the M4 series to beginners, and the HK series to those are familiar with the game. M4? Why is that so? M4s have a high fire rate and accuracy. It is suitable for beginners to spam and kill. HKs do a little more damage so veterans with the accuracy would find the series very enjoyable for owning.
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Rifles are simple. You click and hold to shoot. But, there are secrets in the art of mastering the rifle. Beginners should start to crouch. This reduces the recoil of the gun and increases the chance of killing someone. Veterans which are extremely accurate can strafe left and right and kill with the chance of the opponent not even hitting them with a bullet.

Start to crouch, if you're a beginner. Then gradually progress towards strafing and you will be a master in no time. Trust me.

Now. The AK47. One of the best weapons in the game. It is meant for extremely professional players that can 'headline'. Headlining is a skill that when mastered, will make you dominate your game. It is basically imagining the opponent's head at where your front sight is. Headlining takes up lots of time to master. Even I haven't mastered it yet because I'd rather focus on Sniping.

Personally, I would recommend that you train in the Hunting, for it's close quarters combat. You will be able to train easily. Then progress towards the SD maps if you think you are experienced enough.

This is DrHansPhD, signing out.