I'm planning to buy an upper kit from model 1 and I have a couple of questions.  I plan to use the gun for scoped target and coyote (100-300yds).  I want the heavy free-floated barrel.  My questions are;  5.56 vs .223, won't I have a better bullet selection going with the .223? (I don't reload).   20" vs 24" barrel, is the accuracy and velocity gains much better with the longer barrel?  And last 1-7", 1-8" or 1-9" twist rate.  Isn't the heavier the bullet, the faster the twist rate?  

Thanks in advance for the great info that I know I will get.  This is a great site and I'm learning a lot for my first build.hanksodie072

This will answer alot of your questions:

www.ammo-oracle.com/

Welcome to the site!!

The ammo oracle has some great info waiting for you.

If I were building a gun for your listed purposes I would do this:
5.56 chamber (can shoot 5.56 and .223)
20" barrel, the 24" seems a bit excessive
Any of those twist rates will work for the 55gr, 62gr type stuff.  If I was going to shoot 70+gr ammo I would definitely go with the 1/7.  If I was going to be shooting light loads, i.e. 40-50gr I would use a 1/9 twist.  I dont know enough about the 1/8 to comment but I'd imagine it would perform in between the 1/9 and 1/7 twists.

Thanks for the info, that site helped a lot.  I think I'll start off with a 16" "plinker" and eventually buy an extra upper that I can use for the coyote.  

Thanks again for a great site.
odie072