The R-301 is one of the most popular weapons in Apex Legends and it has stayed in the meta ever since the release of the game. The ease of use is why a lot of people prefer the R-301 to other weapons and if you have noticed the weapon feeling different lately, it is because of a bug.
It looks like even when you aim down sights, the gun retains its hip-fire accuracy which makes it feel very inconsistent. The initial bullets copy the hipfire accuracy in the latest update, which can throw off your aim and cause you to lose gunfights.
Respawn is yet to address when the issue will be fixed
Christopher "sweetdreams" Sexton, who is a pro player for NRG, showed off the glitch on stream and a number of other players immediately spotted the issue. It has been happening to other players as well and Respawn should notice the issue soon.
If you are not sure which weapon to use until the R301 is fixed, your only real option is the Flatline which is also a full-auto assault rifle. There is the Hemlok which also falls in the assault rifle category but it is a burst-fire weapon, which makes it feel very different. The Flatline on the other hand is a little harder to control than the R301 but it can dish out more damage if you are accurate with it.
You could also get used to the new recoil pattern of the R-301 for now until a fix is deployed but it is not recommended as players who have been using the weapon for months will have issues with their muscle memory when adjusting to the new pattern and then switching back once a fix is available.
The Spitfire is a light ammo alternative to the R-301 but it falls under the light machine gun category. The Volt, R-99, and CAR submachine guns can also be viable alternatives with the Volt being the best option among the three if you want more range. The three guns perform similarly and are very competitive weapons.
It is currently unknown when the bug will be fixed so you should keep an eye out on the official Apex Legends Trello board to find out when the bug is addressed.