[Soontobewildcat]

I need suggestions for all uppers including even the oddball ones that will accept a regular AR 15 lower so all calibers including the weird ones but their will be a price limit at most probably 800 dollars but i might be able to bend on that a little bit.

 

[Big Bore]

Almost all will fit the standard AR15 lower, even the ones for the .50 BMG but of course it will be a single shot and will need a stronger hammer spring. The pistol calibers need mag blocks and sometimes special hammers along with caliber specific mags.
Using bone stock AR lowers, on those that use standard AR-15 5.56/.223 mags, it is limited, but all the below use standard AR-15 lowers.
.458 SOCOM (EP opening on upper needs enlarging)
.500 Beowulf but will most likely need tweaking but not a big deal. (EP opening on upper needs enlarging)
.300 Whisper
450 Bushmaster usually needs a new follower and EP opening on upper needs enlarging.

I cannot recall what the .338 Spector uses. I think it uses standard 5.56 mags but don't hold me to that.

The 6.8 SPC needs caliber specific mags.
.30 HRT uses 6.8 mags.

The 6.5 Grendel needs caliber specific mags.

While the 6.8 and 6.5 mags look the same they are not. CProducts told me they are different enough that they should not be used interchangeably.

7.62 x 39 needs specific mags.
5.45 x 39 needs specific mags.

That's all I can think of off hand. Check out AR15.com for more information on this topic because it has been discussed several times over there if you can get their search engine to work. It doesn't work worth a hoot for me and I don't know if it is like that for everyone or because I have a MAC.

 

[Colohunter]

What are you trying to do with the upper? As you can see there a plenty of options, Big Bore mentioned some of the more popular types, and there are plenty more wildcat options. Your intended use will narrow it down a little.

One option I didn't seemed mentioned above is a 22LR conversion. A lot of people are starting to like those since the ammo is so inexpensive.

 

[hailstone]

I've read that 17 Remington, 222 Remington, 221 Remington Fireball, 204 Ruger, 17 Remington Fireball chamberings have also been done in AR-15 uppers.

 

[Big Bore]

As well as uppers in 5.7 x 28 which use the PS90 mag and eject through the mag well. An old 30 round AR mag with the top cut off makes a dandy shell catcher also in this conversion. There are literally hundreds of uppers that fit stock AR lowers if you include all the wildcats. Most based on the 5.56/.223 will not even need new mags.
The sky's the limit so pick your poison.

 

[boonedockssaint]

The AR57 upper is great, really liken it alot!

 

[bsn]

.223wssm,.243wssm,.25wssm

 

[forestdavegump]

The 6.8 works well!