What is the expected accuracy for an AR-15 SPR?
Assume Noveske or BCM upper or …?
Assume factory ammo.
How much better is this than a standard AR-15?
3/4 to 1 MOA with a match barrel and match ammo.
both are needed
then its up to the shooter
Check out some of Molon’s posts here and over on TOS. Instead of one-off three shot groups, he uses 10 shot groups and aggregates them to give a good idea of what a specific round in his ARs are capapble of.
Brain fart, TOS?
That Other Site. 
Molon still mills about here, and elsewhere, but he’s an amazing resource for getting a realistic expectation of mechanical accuracy.