Working on my first build planning. Is there much difference between a 16" and 18" barrels? I keep thinking the 18" would give better accuracy at distance.

Can you use any lower with a A3 or A4 upper? Or do you need a special one.

Thanks

While 18" barrels are marketed as "higher accuracy" pipes, there is actually no real difference between 16" and 18" barrels in terms of potential accuracy.  Go with a good brand or barrel maker, and buy which length you want.

Uppers are uppers, and any in-spec upper should fit any in-spec lower.

Good luck.  This point in planning gets a little overwhelming until you decide exactly what you want to do with the gun, then it kind of "drives itself" toward most of your parts choices.

Pretty much as above. Figure out what you want as a rifle and just build it.

And once you shoot it make changes as necessary.  The leftovers will become another rifle though......

I keep wanting to buy an 18" for a little more velocity, but I'm not going to expect better accuracy than my current 16" setup. Maybe slightly less bullet drop but that would be it.

The only thing to watch out for in an upper is the feed ramps. If the upper has them don't get a barrel without M4 cuts.

Thanks for the info. It does get confusing trying to pick the right stuff. All I want is a rifle that pleases my eye, is reliable goes bang when I pull the trigger, and can be used for short and long defense when I need it. I would like to be able to shoot it for defense accurately. Not much to ask for right.