First suggestion is: don't use the
Grau. It is one of the worst short-range TTK (time-to-kill) rifles in the game. The primary advantage the Grau has is low, easily controllable recoil that allows you to stay on target while full-autoing at longer ranges (>100m), while players using other guns have to burst to stay on target. There are only a few rifles that have this ability (the
Bruen is another which is why everyone is using it right now, and both the M13 and Kilo have very nice recoil profiles as well).
However in short-range/CQC situations, you are severely outgunned if you are using a Grau, because at that distance you are expected to be accurate while full-autoing any weapon you're carrying. So poof there goes the Grau's only advantage.
According to the integral charts I've built to analyze "time under the TTK curve", the best A/R right now for short-range (<50m) is the CR-56. So keep using that. The AK is also very good, despite everyone wanting to hate on its "bad recoil" even though it isn't really any different from the CR-56. Also the RAM-7 is basically a glorified SMG/AR hybrid that has great TTKs for short-range if you can control its terrible recoil.
Here's a quick comparison using TrueGameData's comparison tool, to show how bad the Grau is at TTK, and that the FAL is no longer the best short-range weapon after the most recent weapon-balance update. All 4 rifles here are kitted with Mono Suppressors, their longest barrels, the Tac Laser, a Commando Grip, and the smaller extended mag if it exists (24 for the FAL, 50 for the Grau). Also the Romanian Barrel for the AK comes with an integrated Merc Grip, which allows you to save an attachment slot which I've used to add a No Stock to the AK for max ADS/movement speed buffs for CQC combat effectiveness.
View attachment 1174
The CR-56 has the fastest TTK across all ranges out through 35m, which encompasses any gunfighting you will experience inside buildings and most short-range combat outside. The AK is very close however, and actually grabs the lead for about 5m after the CR-56 drops range. The FAL is just behind the AK through 35m, and then is roughly even with the CR-56 out to 50m, after which it grabs the lead through 57m. However if we're looking at short-range performance here, the FAL being the best from 50-57m is not very relevant. What is relevant is the CR-56 being the best from 0-35m and 40-50m. The old pre-patch FAL used to be the runaway best <25m, but that is no longer the case.
You'll notice the Grau lags far behind the others, 0.15s behind the CR-56 from 0-35m. Thanks to it's longer range dropoffs, it does become semi-useful from about 40-47m, where it's basically even with the AK. However when the Grau drops range at 47m, it becomes far and away the worst TTK weapon again trailing the CR-56 by nearly 0.30s. Again, for a short-range weapon we don't really care about performance outside 50m so that isn't entirely relevant. But at this point the Grau's only claim to fame is being roughly equal to the AK in TTK from 40-47m, while trailing every other rifle significantly inside 40m. If your issue is " as soon as I turn the corner I start drilling them but lose the gunfight even if I did not potato" then you definitely don't need to be using the Grau.
I don't know what kind of loadouts you like to run. I myself prefer to snipe so my secondary weapon has to be something useful in both short and medium ranges. I currently use a CR-56 but also routinely swap in an AK because of it's better midrange performance (50-100m). If you prefer to run an AR/SMG combo, then your AR doesn't have to be good in CQC situations. In that case I would say you can keep using the Grau, or maybe give the Bruen a try, since they are both great long-range weapons with no recoil issues. However based on the wording in your initial post, it sounds as if you're using the CR-56/Grau in short-range situations. So if you are trying to use an A/R as your main primary for shorter ranges, I would definitely suggest keeping with the CR-56 full-time.
However, this...
...just comes from experience. The ability to quickly snap onto a target is a learned skill, and the only way to improve is to play more. I'm not sure if you're on PC or console, but if you're on PC you might want to look into an aim trainer, to help improve your mouse skills.
"Peeker's advantage" is also a thing with server-hosted games. If you are waiting for them to "peek" by coming around the corner to you, their system is communicating with the server first while yours is lagged behind a few ms because the server is having to relay your opponent's movement to you. If you know someone is coming, don't wait for them to come around the corner, but instead jump around the corner at them first. This way you'll be peeking first and you'll already be ADS'd while they are running/sprinting and have to waste ~0.2s to ADS or just randomly panic some hipfire.