  The aCORN experiment measures the neutron decay electron-antineutrino
correlation ($a$-coefficient) using a novel method based on an asymmetry in
proton time-of-flight for events where the beta electron and recoil proton are
detected in delayed coincidence. We report the data analysis and result from
the second run at the NIST Center for Neutron Research, using the high-flux
cold neutron beam on the new NG-C neutron guide end position: $a = -0.10758 \pm
0.00136 (\mbox{stat}) \pm 0.00148 (\mbox{sys})$. This is consistent within
uncertainties with the result from the first aCORN run on the NG-6 cold neutron
beam. Combining the two aCORN runs we obtain $a = -0.10782 \pm 0.00124
(\mbox{stat}) \pm 0.00133 (\mbox{sys})$, which has an overall relative standard
uncertainty of 1.7 \%. The corresponding result for the ratio of weak coupling
constants $\lambda = G_A/G_V$ is $\lambda = -1.2796\pm 0.0062$.
