Officers were called to reports of three men chasing a group of others into DFC Chicken, in Rookery Road, Handsworth, just before 6pm on Monday.
Shots were fired in the shop and the trio of offenders fled the scene.
The other group – which consisted of up to six men – had also left before police arrived.
No injuries have been reported.
West Midlands Police believed it to have been a targeted attack between different groups and CCTV enquiries are underway.
Inspector Jim Church, from Force CID, said: "We are following a number of lines of enquiry but I would urge anyone who knows those involved to contact us.
"Fortunately, no customers or staff inside the shop were hurt.
"They could have been innocent victims of what we believe was a targeted attack between groups."
Anyone with information is urged to call West Midlands Police on 101, or Crimestoppers anonymously on 0800 555111.