Disk Utility is insufficient for creating a bootable clone of your system HD. (For technical reasons that are beyond my knowledge to explain here.)
If you want to clone & replicate your system HD to other Macs, use CarbonCopyCloner from Bombich Software. You can use it for free for 30 days, after that it's $39.99. Mike Bombich is a well respected Apple developer and CCC is an awesome utility. I've been using its many versions for over 12 years and it's perfect for what you want to do. My usage has been to clone, backup and replicate Macs in computer labs (as a system admin) as well as at home for personal use.
CCC can directly clone a master Mac to others via target disk mode - as well as create a .dmg file that you can reuse to replicate to multiple Macs.
Note: I do not receive any compensation for recommending CCC or any other software. My recommendation is based solely on my personal experience as a user.