Recommended path to Carbineer
This information provided by Sylow.
I. the foundation
(holds truth for any carbineer build)
As the old reccomendation doesn't hold truth any more after the CU, i decided to write a new version. Unlike the old guide, i would advise to generally stick to one collumn a time, which at first would be the marksmanship line. (0x00) The only exception of this is that i would advise to get the first box of the Counterinsurgency line, as soon as you have the first box of marksmanship.
Thus it would be 0100, 0110 and then go on with 0210, 0310, 0410 The reason for that is, that the marksmanship line gives you a lot of accuracy, which directly increases your chance to hit, and at the same time offers you the specials "cripple shot" and "leg shot". Cripple shot is a snare, most useful in solo combat, as it allows you to kite(*1) a target without serious problems. Leg shot currently is the most powerful attack in the carbineers toolchest. Since suppression fire lately was fixed, it might be worth a consideration to go for the second box of Counterinsurgency after being 0110. Being 0210 gives you more of striking power but 0120 gives you a new defensive ability which supposedly has the potential to save your lower end. (*2) I dare to warn, though, that this ability has an area of effect, which means that when used without taking care, it easily can attract more enemies on you, which first were not agressive towards you. Careless use of this ability can very well get you killed instead of saving your life.
The first box of the Counterinsurgency grants you the "Charge Shot" ability, allowing you to knock down your target. Not only is a knocked down target unable to move to you (*3), it also takes aprox. 20% more damage while being on the ground from any attack hitting it in that time. (Usually this is one attack from everybody attacking the person, which gets this damage bonus.)
(*1): to kite means that you attack a target, then run away. The target will follow you (like when you are pulling a kite to make it fly) and you can fire at it while running. This tactic doesn't help a lot against a ranged opponent, but is very viable against melee targets. Especially for missions against animal lairs, this approach is very powerful.
(*2): The reason why i am holding back with a clear statement on this is, that suppression fire has not been thoroughly tested in actual battle situations. I hope i can soon make a clearer statement on this.
(*3): be aware that due to lag reasons, a knocked down target might "slide" or "teleport" to you or even be able to hit you, despite it looks like it's many meters away. There is no resolution of this issue in sight, so better keep that in mind.
II. advanced progression
(now it's time to choose your path... decide wisely.)
1. Master Carbineer
(the only true path.)
The further branch of advancement depends on what you want to do. If you are going for Master Carbineer, and it is the first ranged combat profession you are working upon, i actually advise to now focus on Assault tactics. The defences of the Counterinsurgency path might look desireable, the improved Charge Shot definitely is, but you're still low on the speed modifiers, so increasing them makes a difference.
Thus you will then advance for 141x, 241x, 341x and 441x, the Special Abilities line takes combat experience, so is independent of the other boxes and should be trained whenever possible. The counterinsurgency line actually is the last one to complete, the basic version of Charge Shot does the job for quite some time, suppression fire is now helpful but with decent pulling and kiting not necessary. (*4)
2. dabbling for a master of another ranged profession
(You will find the carbineer inside. Give in to the temptation.)
Things definitely look different if you plan to only dabble in Carbineer or if you already have another ranged combat profession mastered. (*5) You then want to be 0440, carbine speed and carbine defence won't be helpful if you plan to use any other weapon.
Additionally, you already bring along some general ranged speed, making speed less of an issue. General accuracy and the defences of the two mentioned lines are what you now are looking for, not to mention that they give you the most useful carbineer abilities. This way, you both improve your fighting capacity as carbineer, while also upping your combat power in your other ranged profession. This way you immediately have more power and flexibility at hand. If you are somewhat short on recovery abilities, the fourth line might be interesting, but currently those recoveries have little meaning and you probably have them from your other profession, anyways.
3. dabbling in carbineer without other combat professions
(A brave person you are, fighting with limited training. Alas, we can just hope that you'll find the carbineer soul inside of you.)
Also, if you plan to only spend a limited number of skillpoints in carbineer without having any other combat profession, the mods and abilities of the 0440 combination are probably the most attractive combination, you will loose out a bit on damage potential due to lower speed bonuses, but the abilities definitely make up for that. (*6)
As you won't be certified for any advanced armour (only your accuracy mitigation is acceptable, the rest is in the novice box and thus not very strong), you are well advised to group for any bigger targets, with some attention on what you do, some kiting and careful movement you're also able to fight and win against creatures one or two levels above you. The combination of legshot, charge shot and cripple shot gives you some nice striking power and the potential to keep the enemy under control. And if things go bad, put suppression fire as default attack, keep shooting and run for your life. (*7)
(*4): If you do some nice kiting against non-social animals (means, they don't all attack you when you attack one of them), you'll also never need the defences of the third line.
(*5): Note that a melee profession won't be helping you with a carbine at all, so i'd rather use the advancement scheme for a new carbineer here.
(*6): In the situation that you only want to be a part-carbineer and it is not your second or third combat profession, i assume that you will go for some crafting profession. Hopefully this crafting profession will earn you a lot of money, allowing you to outfit yourself with some skilltapes which will compensate for your lower speed and accuracy.
(*7): I wish you very good luck.