Welcome aboard!
I'll try to help you out as best as I can,but understand that your questions here require some explanation, so bare with me.
Perhaps the two greatest things that make the .308 round an awesome bullet is that it is extremely accurate-it is the sniper round of most military and police marksmen-accurate to out to (give or take) 1,000 meters, and it has ample power to take deer sized game-which is what most of North America hunts-and it is not too powerful for varmints like coyotes and even hogs-both of which are the targets of a large population of North America.(you probably know these things, but bare with...)
Now lets talk about the AR type rifle. In the past decade or so, there have been huge developments in this product. You can customize an AR type rifle to just about any configuration you can fathom, and the best thing about that is...you can do 95% of it yourself. If you have even the bare minimum amount of gun-smithing knowledge, you can do it all yourself. With the adaptation of the rail system fore ends, you can add all sorts of accessories like night vision optics, lasers, tactical lights, bipods, I.R. illuminators, etc. With the adaptation of the latest in quick detach return-to-zero mounts, you can switch optics in a flash and go from short range C.Q.B. optics to medium or long range optics with minimal shift in point of aim/point of impact.
The AR-15 is great, but the .223 is lacking in a lot of categories strictly due to the fact that the .223 lacks two of the things mentioned earlier...range and knock down power. So, when a shooter cycles a round into his or her AR-10, he is usually doing one of the following: Hunting deer sized targets (or hogs), trying to produce sub MOA groups, or trying to hit the x-ring and/or a steel silhouette at long range. Most AR-10 shooters are not using their rifles to run a shoot house or clear a building. I am a tactical user myself, and from a tactical standpoint, I would not want a .308 over a .223 in a close combat situation strictly due to over penetration issues. (fact is, I think even the .223 is over powered for this application.)Thus, this is the reason that most AR-10 users do not opt for the collapsible stock...most of us shoot our AR-10s for precision/hunting work and prefer the stability offered by the fixed type stocks. There are a few situations in which a tactical "sniper" or designated marksmen rifle would benefit from a collapsible stock, (rappelling, helo insertion, etc.) but in large the collapsible stock market belongs mostly to the AR-15 entry/C.Q.B. gun world.
As far as your question pertaining to the piece by piece vs. buying a complete rifle is concerned, that depends largely on what you want to do with it. If you want to hunt deer or hogs and you only plan to shoot 100 to 300 yards, a stock gun with some good optics will work fine. If you plan to shoot long range or if you want a rifle that can shoot 1/2 groups or better at 100 yards, you might be better off building your rifle from the ground up. I can point you in the right direction for either...Simply assess what your proposed rifle's basic function will be, let me know, and I will be more than happy to assist.
Welcome to the site...I am sure you will find a wealth of information to aid you in your quest....As Mlotz said I completed a build...but it was a M-15...but for the most part set up like my AR-10...
As TX stated...it depends on what/how you are going to use it for..and how far....short to medium range a Carbine will do the job...medium to long range...then the rifle length....
Now for the build.....it is my PERSONAL opinion..that unless you have a great deal of experience with the rifle and the platform..it would be better to buy a complete rifle rather than build...to many have "built" one and spent the next several months ironing out the bugs....which really could just piss a person off....
I also will be glad to help with any questions if I can...I am no "expert" but I have a fair amount of knowledge with the platform and accessories...
Just keep in mind one main rule...."PERSONAL PREFERENCE" is what matters...what works for me or others may not for you....go with what YOU want....
I hope this is of some assistance....
BMS
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