I just finished my Aero precision M5 build.  I ordered a complete upper with SS 18" barrel rifle length buffer tube spring and buffer, Magpul PRS stock, Aero black nitride BCG.  Ordered all parts from Schulyer on recommendations here.   My issue is that the bolt is very difficult to pull back.  It feels like the recoil spring is too stiff.  I have only fired 20 rounds through it and the brass lands in a neat pile about 2ft away from the ejection port.  I also had one instance where the bolt did not hold open on the last shot.  I noticed it getting better the more I worked it and shot it but I think this rifle would do better with a lighter recoil spring.  Where can I get lighter springs for the ar10 platform?  Everything was lubed up with frog lube prior to shooting.

it has noting to do with the recoil spring. this is a common occurrence with 308 AR's, it just needs to be broken in. my M5 build was so tight after I built it I had to mortar it just to get the bcg rearward. also remove that froglube and use some CLP or mobil.

I put an adjustable gas block on my aero M5, at the time I needed a stiffer spring but decided on gas block and it took care of all my problems

An AR15 carbine spring will swap in.  It probably won't have enough strength to close the carrier every time.  I ended up going with Sprinco RED springs on my 6.5 builds to ensure the carriers fully closed every shot.

My m5 was exactly the same. The bolt is so tight in the carrier. After a few hundred rounds its easier, but the spring is heavier. It's not going to cycle like an ar15.

Like others have said, it'll get better as you put more rounds through it. Mine likes Mobil 1 for lube.