The manufacturer does not provide the length of the strap but it will accommodate most common bullpup rifles/shotguns, like the IWI Tavor.
The larger strap is 14" long. The smaller is only 4 " long...Just for a barrel. You can position the straps on the velcro side-wall as close as 11 inches apart and as far as 24 inches apart. You could sew a Velcro extension onto the supplied straps if you need more.