I am getting ready to buy a upper for my recently compleated double star lower. i was kicking around the idea of a j&t m4 , but i have been thinking that i want something that  will shoot respectably at  400-500 yards. what do you guys recomend.?

Lets start off with what you are looking for. Do you want something that looks relatively "military" (ala Special Purpose Rifle) or are you just looking for any AR15 that can shoot out to the distances you specified?
Also, what is your budget? Of course the standard answer is "As little as possible", but what is your upper limit?
I have 2 SPR's, both a Mod0 and Mod1 and both shoot superbly out to 700yds. If you are looking for something that looks military, you can go with either of the SPR's but they will cost you. You can do a Mod1 on a budget though. How does this sound:

White Oak SPR barrel with matching bolt from Adco
SPR faux brake and collar from Adco
Yankee Hill rifle length lightweight FF tube
Bolt Carrier and parts
Knights 600m rear sight
Yankee Hill rail mounted flip up sight

That will give you a damn good looking rifle for a minimal amount of money, especially if you shop around.
Then again, you can go with most anyones stainless heavy barrel upper and it SHOULD shoot well out to those distances.


The bottom line is we need some sort of budget to really help you.

And then buy one of these www.ultramag50.com/specs.html

Check out BravoCompany.  They build some really nice SAM uppers that will definately be right up your alley.

I am looking at around 500 for a complete upper. I have been looking at some of the j
&t free float varmit uppers. maby the 24" ported f.f in stainless. Any have any experience with these