Trying to decide what you should add to your carbine is like arguing fashion. At some point you have to accept it's mostly about looking cool and fitting in. So what point determines when accessories become more about fashion than operational? I'm glad you asked.
As a former Navy SEAL I can reassure you that most of the things you think you need you really don't but we tend to convince ourselves in life that we do. For instance, take the vehicle you drive. I would say that you need a car to move around day to day, but lets break it down some with the words want or need. Do you need the exact vehicle you have or did you want the look and luxuries? Size, model, power windows, and all the other bells and whistles? It does make our lives easier at times but that translates into comfort or fashion. At the end of the day the basics get you from point A to B without issue.
Another factor that really pushes this agenda is what we see on social media. Shooters that have never stepped foot on a battle field or enforcement position yet have more gear on armor than a real operator ever would. Their rifles look like Swiss Army knives at times. You have to be careful of who and what you listen to. Just because they have followers doesn't make them knowledgeable on any level. Most took a few classes here and there and watched a few videos, adapting the "operator" look. With that being said this is why we live in the greatest nation in the world where we can do what we want with our money and time.
The very first thing that should occur before any accessories are considered is determining what you will be doing and expectations, meaning, how far will I be shooting or expect to shoot? Am I setting this up for combative measures, fun, competition, hunting, mid/long range, and a few more considerations. Once that is determined you should have a good idea on what caliber, barrel length, and stock/brace you want to go with. I can't tell you how many students come to class with weapon systems and gear that are nothing less than atrocious to say the least and it is ok. We only know what we know but had they followed this system of approach it would have prevented a lot of unnecessary steps. Unless you start with this you will often find yourself with optics and other off the wall accessories that don't work so well which leads to more money spent. Below are the most common accessories and descriptions of.
Caliber: The caliber you choose should be determined by how far you want to shoot and what you expect to achieve knock down power wise. This is studied in energy and what is called the maximum effective range which means it produces the same results at that particular distance round after round. Outside of that it is hit and miss and cannot be trusted to perform consistently due to environmental variables.
Barrel length: There is a lot of debate on 16" versus 10.5" and its effectiveness. Here is what I will tell you. The longer the round can stay in the barrel it has more velocity and stability which translates into longer distances and energy delivered down range. With the typical .223 round, a 16" barrel is roughly 222 ft/sec faster than a 10.5" barrel. With a length difference of 5.5" that equates to about 40 ft/sec per inch. I think we can agree that a 16" barrel is overall better but are you going to shoot out past 500 yards? I run a 10.5" most of the time and I am more than combat effective. If you are shooting through a car door at 500 yards it would be more efficient to be behind the 16" barrel as well as using rounds that are classified as light armor piercing.
The happy medium of the two is a 14" barrel. My recommendation in my professional opinion is go with the 14" or 16". Speed, accuracy, and energy are more important than a few inches. (That's what she said)
Stock: The stock should be determined by stability and mechanical needs. i.e. long range, mid range, CQB, or an overall battle rifle.
Trigger: Good luck on choosing a trigger. Single stage, two stage, adjustable, weight, reset....... Unless you are serious about shooting stick with a stock trigger. If you want the bells and whistles, I like a single stage Timney or Geisselle personally. My only advice here is don't go too light or you will end up having light strike issues. Stay above a 3.5 lb pull weight.
Optic: Your optic choice should only be chosen after you decide what caliber, and overall area you will be operating in. Distance and speed as it pertains to target acquisition are the biggest determining factors for optic choice. Getting into optics is an entirely different blog and mind you it is endless. Again my professional recommendations for a great optic is a red dot with a 3x magnifier, EoTech with 3x magnifier, Trijicon Acog, or something along the lines of a Sig Sauer TANG06 1-6X-24 tactical scope. Just a pro tip. If you can afford the Trijicon Acog go with that for an overall amazing optic.
Back up Sights: It is always a good idea to have back up sights. Even high end optics can fail and you don't want to be standing there in a gun fight wishing you had mounted one. The most common back up sight is a micro red dot with a 45 degree offset plate. I run a Vortex Venom micro red dot or Magpul flip up sights. Both work amazing but the Magpul requires you to manually activate.
Light: Deciding to purchase a light is about like determining if you need 4 wheel drive on a vehicle for your daily life. Truly we can justify it but at the end of the day do I really need one? If you rifle is for fun, you don't shoot at night, or you lock your rifle in a safe at night, then it doesn't make sense to have a mounted light right? If your rifle is part of your home defense system, and/or you shoot at night, then absolutely. The only thing I will say about lights is the more lumen you have the brighter, but the quicker the battery runs out. You will need to play with different lumen to determine what works best for your operational environment.
We could continue going into accessories like suppressors, Peq-2 IR, and such, but from an operator's perspective don't get caught up in this nonsense and I'll blow the doors off so you have a better understanding of why I say this. All the night vision videos you see on social media except for a handful of people rent the gear and film videos. Is there anything wrong with renting and enjoying our freedoms? Absolutely not but don't spend money on things because you think it is a necessity. Do I have them? It's no ones business. (:
Have a great day and God bless,