[lammps-users] to pack grains in silo for further measurements

Dear LAMMPS users,
I want to measure stresses at the bottom of silo. First grains in silo need to be packed. I have drafted input file but I can not insert specific numbers of grains in the silo. How can I insert 50gm of grains in silo? Should I use SI units or lj? And when I set velocity value along z-axis ( my silo is type cylinder which is along z-axis), then error occurs that “Velocity command with no atoms existing”. What is wrong with my input file. Should I set value of g as 9.8 or 1.0?
Thanks in advance…

my input file is:

atom_style granular
boundary p p fm
newton off

region cyl cylinder z 0.0 0.0 5.0 -10.0 70.0 units box
create_box 1 cyl

neighbor 0.2 bin
neigh_modify delay 0

pair_style gran/hooke/history 2000.0 NULL 50.0 NULL 0.5 0
pair_coeff * *

timestep 0.0001

fix 1 all nve/sphere
fix 2 all gravity 1.0 spherical 0.0 -180.0
fix 3 all wall/gran 2000.0 NULL 50.0 NULL 0.5 0 zplane 0.0 2000.0
#velocity all set 0.0 0.0 1.0

region reg cylinder z 0.0 0.0 4.8 10.0 69.0 units box
fix ins all pour 200000 1 300719 vol 0.13 50 region reg

compute 1 all erotate/sphere
thermo_style custom step atoms ke c_1 vol
thermo 1000
#thermo_modify lost ignore norm no
#compute_modify thermo_temp dynamic yes

dump id all atom 1000 dump.silo
run 250000

#unfix ins
#fix 2 all gravity 1.0
#run 25000

You can use the fix pour command to pour granular particles into
a container. I would look at the examples/pour/in.pour scripts
to get started.