I have started on my first ar-15have
I want a heavy varmint barrel 16" or 20"

Any tips?  I have been looking on Wilson barrels

I will be shooting up to 300 yards..

Quoted: I have started on my first ar-15 I have a RRA A3 upper, KT-16 lower and a ACE stock I want a heavy varmint barrel 16" or 20" Any tips?  I have been looking on Wilson barrels I will be shooting up to 300 yards..

18"

Both the 16 and 20" will have nearly the same accuracy potential at 300 yards, but the 20" will give you a 100-200 fps higher velocity. If you handload, the 16" is fine for precision work out to 300yards, because you can tune a load to the barrel. If you use factory loads, the 20 will probably give you an edge, just because faster is usually more accurate. You may want to research "how to Develop a handload". Each barrel likes a different load. Good luck.

if it is pdogs you're after, that range may lengthen with time, and a 24" would be my vote.  i like the extra velocity and weight.  

if you're after yotes and such, and will likely be in and out of the pick up often, then stick with a 20" barrel.  the 20" units offer a little more versatility in my opinion.  the length is important, but i'm curious which barrel you're buying.

the wilson units i've run are great.  i hear many good things about the white oak armory stuff too.  

HTH.

good luck and good shooting.

-septic tank

I went with an Olympic Arms 20" SUM complete upper for my first build.  I have not regretted it.  It shoots better than myself most of the time i.e. right around .6 moa with WWB 45 gr. HP's.
Are there any others running the same setup?
I also went with a CMC single stage trigger.  

I also went with a CMC single stage trigger

Are You satisfied with this trigger?

I was thinking off putting in one too...

Yes I am.  I went with a single stage because I have always shot bolt rifles with single stage.  I use the gun mainly for predator calling and it is my truck gun for targets of opportunities.  I think the two-stage might be better for target shooting i.e. bench work, but I prefer a single stage for most of what I use the rifle for.