You will have to tell us if they are loaded or empty, whether they are shotgun shells (and the gauge), rim fire or center fire and the caliber.
how many pound equal to 20000 firearm gun shells?
No
none
Many fine 20 gauge shells are made.
This gun is a Rifle
There are 7,000 grains in one pound of gun powder. Grains are measured at 437.5 grains per ounce.
A Paixhans gun is an early naval gun for firing explosive shells.
gun show, gun shop
There are over 20000 on the books.
1 dram = 0.003 906 25 pound
Artillery
7000 grains of powder, lead, or peanut butter to one pound.