Vesta lists its formats in the manual. .grd is on P136. Nothing particular to recommend that specific format, just that it's familiar from e.g. rmcprofie. You'd need access to map values to write a .grd file......
https://jp-minerals.org/vesta/archives/VESTA_Manual.pdf
I haven't looked at the fcf for>15 years but list 3 rings vague bells. I've pasted something below which was on my hard drive called "topas_works.fcf" and dated 2003. Please check carefully though....I haven't got proper notes to hand to be sure it was correct.
John
data_
_shelx_refln_list_code 3
_cell_length_a 2.8599
_cell_length_b 14.64044
_cell_length_c 5.25965
_cell_angle_alpha 90
_cell_angle_beta 90
_cell_angle_gamma 90
_shelx_F_squared_multiplier 1
loop_
_symmetry_equiv_pos_as_xyz
'-x, -y, z+1/2'
'-x, y, z'
'x, -y, z+1/2'
'x, y, z'
'-x+1/2, -y+1/2, z+1/2'
'-x+1/2, y+1/2, z'
'x+1/2, -y+1/2, z+1/2'
'x+1/2, y+1/2, z'
loop_
_refln_index_h
_refln_index_k
_refln_index_l
_refln_F_meas
_refln_F_sigma
_refln_A_calc
_refln_B_calc
0 2 0 4.74 0.00 5.43 0.00
0 2 1 1.82 0.00 0.63 -1.34
0 4 0 4.25 0.00 4.60 0.00
0 4 1 1.71 0.00 0.72 1.13
1 1 0 5.04 0.00 3.93 -0.00
...etc