the one on the left.   Is this what a burst hammer looks like without the spur for the sear?

The burst hammer is the one on the right (with the autosear portion cut off). The part that sticks out where the disconnector engages is where the burst disconnector catches.

Quoted: The burst hammer is the one on the right (with the autosear portion cut off). The part that sticks out where the disconnector engages is where the burst disconnector catches.

The hammer at left is a "SP-1" (.223/AR-15 semi-auto) hammer,  the hammer at right is in most respects a neutered M16 hammer, making it semi-auto legal..

As noted, the burst hammer has a wider diconnect shelf asseen in the pic, but the burst hammer also has a smaller shaft OD there where the spring wraps around for the burst cam on the right side...   If that post is same OD as the Sporter hammer, and not finish machined, then it will not accept a burst cam.