Increasing shooting skill at shooting range

I read you can improve your Shooting stat at the gun range. I am only interested in GTA Online here.

Can it be done solo or does that have no effect?
What do I have to actually complete at the gun range to increase my stat?
If I do a best out of 3 against someone how much does that actually contribute to my stat? What are the factors that will determine how much? Do I need to win?
I read that gold/silver/bronze medals give you 3/2/1% increase in shooting stat. I have never seen anything about medals when doing it online, it's just me against another guy trying to shoot targets. How do I/we get medals online?

Best Answer

Yes you can do it solo.

2 and 4. From the GTAV wiki:

The player's skill in handling firearms. Dampens recoil, reduces reload time, heightens accuracy, and increases ammo capacity. Increase this skill by landing hits on enemies, scoring headshots, and successfully completing Shooting Range challenges. The player can raise his shooting skill with the gun challenges. It will raise at 3% for gold medals, 2% for silver medals and 1% for bronze medals. Note that Online characters reload at maximum speed regardless of their shooting skill.

For the 3rd question I do not know the ratio at which shooting goes up but just shooting at a range for 20 minutes or so I got almost a full bar(20%). Shooting is pretty fast to level up and it will come from just doing jobs/heists/DMs pretty nicely but if you want to grind it I'd say shooting range is the best way to do that.

E: Also if shooting range seems boring you can do Survivals with friends(or solo!) which is also a rather effective way, just remember to aim for the head and it will go up faster than from just body shots.