I was wondering what material are the Colt/Bushmaster lowers. This is to assess whether I should buy a RRA stripped lower for my next rifle or spend more and find a forged.

I was under the impression that the lower is not a stressed member on a AR type of rifle.

And also who has both and can give some opinions on both.

most lowers are forged aluminum.  this includes RRA lowers.  dpms makes both cast and forged lowers.  just buy the RRA lower, you'll be happy with it.  

Thanks Inferno. I will go with a RRA Post-Ban lower from Eagle Firearms.

Now time to go pick out a kit from Model 1. Something good for accuracy and reliability. Maybe the 20" Post Ban Standard Rifle kit with a Stainless 1:8 barrel and NM front sight.

That should be a good starting point for competition shooting right?

You should ask questions about the configuration of a rifle for competition over on the Competition board.  There are specific parts you should include in your rifle.  There is no such animal as "National Match" parts for an AR, however there are makers with parts suitable for a match or service rifle.

8 inch twist is a good choice, however 7 inch is better if you ever decide to shoot a 90 grain bullet.  The 7 twist barrel with shoot 52 grain Sierra MatchKings just fine, also.

An AR lower is not "unstressed", they just don't have to work very hard to hold the trigger group and a magazine.  You should go with the forged lower anyway.

As far as your kit choice - I don't know where Model 1 gets their barrels, but they are likely to be plenty good if you are interested in  starting out in NRA Highpower competition - just about any AR that is assembled correctly from good parts will shoot 1 inch groups at 100 yards.  The Highpower game is more dependent on the shooter than the rifle when you are new.  However, don't scrimp on the trigger - get a RRA two stage.

7075-T6 forged aluminum.   The standard material for all top quality AR lowers and uppers, and the correct material for mil-spec M16 family uppers and lowers.

I personally would settle for nothing less.  No cast lowers for me, thanks!   Not when forged costs only a few bucks more and is assuredly stronger.

CJ