A calculation technique is proposed for estimation of the second moments of quadrupole frequency distributions in FCC metals with an ensemble of edge circular dislocation loops. Available data show that such type of dislocation loops predominantly forms from plane clusters and vacancy accumulations in neutron irradiated FCC metals. Calculation results are presented for copper and aluminium with dislocation loop density about 1017 cm-3. Calculation data are in agreement with NMR study results for irradiated copper.