I just picked up a new Colt AR-15 A2 Carbine.  It has a fixed carry handle so I am thinking of getting another 16" flat-top upper.  Question: any suggestions of make and suggestions of barrel twist 1X7"?  Seems most vendors sell 1X9" barrels

why do you want a 1:7 twist? Since you have a carbine you arent going to be doing 'precision' shooting I'm guessing. I'd go with 1:9 since most ammo is 55 grain but you could get 62 grain and be fine with 1:7.

Only Colt and DPMS offer 1/7's in 16", Bushmaster offers 1/7's in 14.5".
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Here's the way I look at it (but a lot of others know much more about this than I do):

If you are mainly shooting 55grains then 1x7, 1x8 or 1x9.

If you are going lighter than 55gr then 1x9 or 1x12.

If you are going heavier than 62gr then 1x8 or 1x7?

I myself am building a flattop carbine but want to shoot 55-77gr (edited to add: but also want the option to try slightly lighter bullets) so am getting a 1x8".

Hope that helps.

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AFAIK, only stainless steel barrels are offered in 1/8.

Yup, gonna get a 1:8 stainless  16" RRA barrel.
[img]http://www.rockriverarms.com/images/barrelassembly.gif[/img]

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The military chose 1\7 to stabilize the tracer bullet. 1\9 will shoot ANY bullet from 52 gr. to 75 gr. If you need to go heavier than 75 gr, you will need a 1\8 or faster twist.

I have a 1\8 on my target rifle and shoot 55 gr through 80 gr bullets with no problems. If you are going to use varment rounds lighter than 52 gr, you MAY experience problems with the lighter rounds sheding their jackets. For that you will need a 1\12 barrel.

I can't add much to what's already been said but here's my 2 cents...[;)]

If you are building a rifle for match accuracy or bench rest go with 1/9 or better yet 1/8.

If you are builing a rifle for fighting or SHTF go with a 1/7, fully chrome lined, 4150 steel and a 5.56 chamber. The 1/7 will shoot the cheap 55gr mil-surp the excellent 77gr MK262 and even the 100gr ammo if you want.

IMHO, at this time the 1/7 is the best compromise for fighting carbine/rifle because It will let you shoot the any of the proven milspec 5.56 ammo used for combat.  

The military might have originally used the 1/7 to stabalize the long tracer bullet but I believe with the advent of the MK262 and other heavy rounds it's been proven to be a good choice.

YMMV[:D]