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Maverick, thanks for the information. I didn't order a complete lower from PSA because I wasn't sure of the buffer tube situation. Will probably order a complete PSA upper once lower is complete though. Will that Aero M5 .308 carbine buffer kit work with any of the complete PSA uppers? Aero also offers a rifle buffer kit, but it is cheaper and 6061 aluminum.
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That depends. If you go with a 308 RIFLE buffer kit you will need to use a 308 Rifle buffer with corresponding 308 rifle spring. If you go with their "308 CARBINE" kit you will get a standard mil spec AR mil spec buffer tube with "shorty" 308 buffer and proper spring to match. If going the "RIFLE" route, you will be limited to A1/A2 (and similar) fixed stocks. If going the "CARBINE" route, you will be able to use all the adjustable stocks that AR carbines use. Aero does not use the "extended" tube that PSA/Armalite use, so any standard AR dimensions apply as normal.
For both my G1 and G2, I ditched their "Extended" tube and went with standard mil spec AR tube with Guntec 308 "carbine" kit (Aim Surplus has a great price on them).
I went with the Aero Kit for an Aero Precision M5e1 build (that also worked great).
PSA chose the longer "extended" tube to be able to use standard AR buffers. That's fine, the problem is they have no idea what they're doing with buffer springs (as evidenced with numerous complaints of coil bind with the longer, and higher coil count, spring). They do seem to have a proper length spring, but they obviously don't know when to use which, and if you order it (as I did), it's a crap shoot as to which one you get (as with my order). They need to learn/understand that a 308 RIFLE length spring does NOT belong in ANYTHING other than a RIFLE buffer tube.
Both a standard AR carbine tube, and the "extended" length (which PSA calls their PA-10 tube) REQUIRES the use of the same 308 CARBINE spring (the same 10.5", 28 coil spring is used in both standard AR carbine tubes AND extended tubes. SAME SPRING). Until PSA stops using RIFLE springs in their "extended" tubes... stay FAR away from them (or you WILL have coil bind issues).
It's hit or miss... sometimes PSA gets its right.. mostly not. Again, IMHO, don't gamble with it. Just go with a manufacturer that understands the difference and adheres to it (such as Aero or Guntec).
Even if you had ordered a complete lower, it's not all bad. You'd just need a proper 308 "carbine" spring. If naked, you'll need a mil spec tube, 308 "shorty" buffer and (same) "308 Carbine" spring. Not a huge deal.
And yes, upper has no effect. Any upper combo will work with any lower combo, so long as that lower combo is set up properly (as mentioned).
Keep us posted on your PA-10 build. I actually LOVE the PA series receivers, I just wish PSA would stop making complete rifles until they know/understand what they're doing (and use the proper parts). Buffer systems are complicated, and PSA would have far less complaints if they had a clue what they're doing.
Not to rag on PSA though. I'm sure they have guys grabbing parts from bins that have no idea what's for what. The 308 assemblers should really be a separate bunch that understand the differences (and which parts mate with which).
ETA: I forgot to add... if you get a complete upper, PLEASE do NOT get a fixed FSB upper. Get a FF upper and ditch their gas block for an adjustable version (I recommend SLR click adjustable). There is FAR more variance with 308/7.62N than with 223/5.56N. Unless you want to chase a very expensive (buffer related) rabbit hole, go with an adjustable gas block (solves any buffer related issues).