I have Bushmaster XM15-e2s hbar that was a police trade in. This is an older rifle built in Windham Maine prior to Remington moving production. This rifle is pretty original other than, sling mount receiver end plate, later mil-spec carry handle, and kns ball tip extended height front sight to...
I found these awhile back and know nothing about them but they make 10 and 16 inch barrels
https://www.zfi-inc.com/product/igb-austria-match-grade-hexagonal-10-threaded-barrel-for-10-auto-40s-w-45acp-calibers/