Originally posted by: slashbinslashbash
Just to echo/expand a few other things in this thread...
AIM Surplus is a great place, I bought a bunch of mags from them pre-election and they have held the same prices all the way to now, even when they were sold out and on constant backorder for all high-cap AK and AR mags. Now they are all pretty much back in stock, and at the same prices ($10 for a basic AR 30rd mag, $14 for the Magpul PMAG's and $11 for a basic AK 30rd mag). I am impressed. If you want AK's then they usually have a couple to choose from, and another good web dealer is classicarms.us . I bought my first 2 AK's from them as well as a few milsurp bolt-actions. Of course for either one you will have to have the gun (or receiver, which counts as a gun) shipped to a local Federal Firearms License (FFL) dealer which will usually be a local gunshop which will charge $20-$40 to receive and process the gun transfer to you.
Del-Ton is another great store. I ordered my 16" midlength kit from them in mid-November. It took till mid-December for me to get it, but I did, and it works great. Another good place for AR kits is Model One Sales,
http://www.model1sales.com They have a lot bigger selection of calibers and configurations than Del-Ton, but for some reason they don't carry a mid-length kit, which is what I wanted for my first AR. But their prices (under $500 for a basic kit) and quality are comparable to Del-Ton.
As for the lower receivers, it doesn't matter what is marked on the lower with respect to caliber. A lot of lowers just say "Multi". The upper (actually, just the barrel) is what determines the caliber on an AR-15. I would recommend getting a barrel with a 5.56 chamber since you can then shoot .223 (commercial) and 5.56 (milsurp) with no worries. If you are building a tack-driving varminter, then maybe go for .223 since you can generally get more accurate .223 loads, which will not be as accurate in the 5.56 chamber. But if you are building a dedicated long-range varminter, why not go for .204 or something else (.204 kits are available from Model One). Also some companies offer the "Wylde Chamber" which is a cross between .223 and 5.56, is safe to shoot both and gains some accuracy over the 5.56 chamber when shooting .223-spec rounds.
Contrary to popular belief, there are differences between lowers when it comes to stupid little things like clearances. I have an Aero Precision lower that I built using a Del-Ton kit, and my brother-in-law has a DPMS lower that I built using a Model One kit. It was easier for me to get most of the lower parts into my lower, but the Del-Ton machine scres that attaches the pistol grip to the lower was too long for the hole in for my Aero Precision lower; I could not tighten the pistol grip tight enough. The Del-Ton screw fit just fine in his DPMS lower. Whether this is a problem with the lower or with the screw, I couldn't tell you; but these things apparently come up from time to time. It was easy enough to fix mine with a few washers from Home Depot to build up inside my pistol grip. And it was much harder to get the front pivot detent put into his lower than into mine. I would think that the spring holes are drilled to slightly different depths, which made mine much easier to install. On his, we actually lost his detent because it was sent flying across the room by the spring.
We built the two AR's in the same day and it wasn't so hard, but I can't say that I really relish doing it again. I certainly would not ridicule anybody who decided to buy a complete, assembled lower like the CMMG that AIM has for $209 (the rest of the assembly is very easy). And then go ahead and buy the whole kit from Del-Ton or M1 just to have an extra lower parts kit which you could sell for $60-$70 no problem. The dimensional aspects of the various lower receivers are probably the biggest difference you will find, but it is hard to call any one of them better than another because of it. Another difference is in the finish. If you look at the CMMG receivers on AIM, you will notice that they have a Teflon finish over their anodizing, which gives them a semi-gloss appearance that I think looks pretty good (I have seen CMMG lowers in person) but might not match most upper receivers which are just anodized (although I got a Teflon'd upper in my Del-Ton kit, so I'm going to eventually get a CMMG lower to match with it). In general the anodized parts look more of a dark grey color while the Teflon parts look more of a true black. It is hard to say though, and if you want a perfectly matched gun then you will either have to buy a fully assembled rifle or re-finish everything once it's assembled.
Moving on to other differences.... look at the two images of the Superior Arms vs. the CMMG:
http://www.aimsurplus.com/acatalog/cmmgl001back.jpg
http://www.aimsurplus.com/acatalog/ars15back.jpg
Open them up in two browser tabs and switch back and forth between the tabs. You can tell that the CMMG was machined more precisely, just the way the various cuts show more of a definite line between the two different surfaces, while the Superior Arms seems to blend together a bit. Anyway, probably not very important, but it would feel different in your hands.
As for recommended configurations, I would go for something basic for your first kit. The standard fixed-stock 20" AR is a classic, as is the M4-style carbine with a 16" barrel (minimum legal barrel length in the US (well OK, you can get shorter barrels but you will have to pay $200 tax and go through a separate and lengthy background check for that)) and collapsible stock. Get one with a fixed front sight (it won't get in the way, even with optics; it will disappear with magnified scopes, and it will co-witness with red dots) and it's your choice on the rear sight, whether you want the built-in carry handle/rear sight or a flat top that will require you to buy a bolt-on rear sight. The flat top is better for adding optics, but it's not too hard to add optics to a carry handle either. If you want a magnified scope for hunting then the flat top is obviously better, but if you want a red dot then you could go either way. The iron sights on AR's are pretty good, and of course they are more reliable than any kind of optic.