One way that I just tested and works with some tweaking... Make two circle sprites, one larger than other slightly so when they overlap you get your "ring" when inner sprite color is set to backgrounds. You can make circle sprites in Construct2 sprite editor by using paint brush and setting its brush size to 260ish for large and 250ish for inner.
Click the crop tool to remove excess from around edges and then edit collision polygons by right clicking circle and selecting "guess shape", tweak and add points as needed.
Once you have your two circles arrange them on layout so your ring is showing.
Use System Every X Seconds and set to whatever you like... I used 0.1 and it worked good but if you want it faster than use 0.0#. You could use every tick... but why.
I made a sub-condition off the Every-X-Second that does a Sprite (your bullet object) is overlapping inner sprite and then right click and choose Invert.
The action is Sprite (bullet object) bounce off outer sprite. You would also put your angle stuff here to keep it angled back inside.
It worked as intended but would need some tweaking to be perfect.
Another method since its a circle and the distance from center will always be the same, would be to get the center X,Y coordinate and then have the bullet object check its distance from center (var) with a center.X,center.Y, bullet.X,bullet.Y action and then react if its greater than your "ring" distance from center.