there are to many AR parts suppliers out there.....AIM is not mass friendly.
Are you building to build or trying to save money.
Saving money is a bit hard to do on a basic AR build unless you get good group buy prices and lots of free shipping.
I will give you a example. I was going to build a National Match Service rifle nothing super fancy just a NM model like RRA.Armalite,Bushmaster.CLE,WOA put out.
After priceing out all the things needed I was spending more on building the upper than a complete rifle from RRA.bushmaster,armalite ect ect.
Gunkings.com is another great place as they have odd ball madness sales. AR15sales.com is another good source for parts and uppers STAG,LMT,RRA
I purchased a good amount of AR parts for a complete Frankenbuild from places like E-gun parts, bobs gun parts, copes, and other surplus type web sites.
I even purchased the colt AR kits that where offered a while back with new barrels. Thing I did not know is the barrels where "in the white" and did not have the crowns finished or machined for the front sight pins. I lucked out though and found a willing trader to trade my barrel for his used carbine barrel.
sarcoinc can be hit or miss.....but find them to be one of the cheapest surplus dealers, Be warned customer service is not very good. products are hit or miss and tend to be just under as they describe. Last I looked though the barrels on the kits are coming in finished and fitted with front sight or they are finding surplus barrels to toss in the kit ?
http://e-sarcoinc.com/originalcoltgim16a2completepartssets.aspx here is one of the kits I got but at the time the barrel was note finished or even threaded for muzzle device. It also was a bit cheaper. I think they had the barrels finished or found a new supplier. This picture shows the delta ring seperate from the barrel nut. So you need to nock off the front sight to install delta ring ? still hard pressed to find kits less than these. mate it with a good group buy priced lower your into a AR for under 600.00 ? or you can buy one all done for you a little more ?