My question is, why on earth would you go to an extra power carbine spring (Sprinco blue) in an A5 length rear extension? The Blue, and other springs meant to smooth out supressors in carbines are not the same length as a new A5 spring from Vltor. They're a few coils shorter. You'll loose a lot of resistance over the Green spring which is meant to fill a rifle length RE.
I run 3 suppressed 5.56 AR's (SOLGW 14.3" mid, Centurion 12.5" carbine, and a Hodge 14.5" mid) on BCM/Vltor A5 length RE's, A5H1(with Hodge's optimized gas port) and A5H2 buffers using the Sprinco green springs. All are flat shooting without hiccups, with or without the cans. The cans are a YHM Turbo and Dead Air sandman K's
I also run a 13.9" mid gas 6.5 Grendel (A5H3, green), 18" rifle length 5.56 (A5H2, green) , and an 18" mid gas .308 (with a Tubb's flatcoil spring/A5H3) with great results supressed or not
Nick Wantland from Vltor doesn't recommend any other spring for use with the A5 system but the Sprinco green in small frame AR's. He also admits that the Sprinco has an exponentially better service life. The A5 comes with a mil-spec rifle length spring. Using a carbine specific spring in the A5 system was setting it up for failure.