I love gymnastics!! I'm a firm believer that it's one of the best ways to teach a horse to use its body over fences and teach a rider to stay still. We always have a gymnastic of some sort up in one of our rings so depending on the horse I usually do them several times a week.
So I haven't jumped 3" without stirrups/reins with a little pony... but once I was working with a jumper (with a habit of stopping) over a gymnastic that was:
2"9 vertical (one stride) 3" vertical (two strides) 3"6 oxer
And over the first he landed really hard and my helmet fell completely over my eyes! Apparently the padding was worn out... I did the rest of the gymnastic in completely darkness! I cussed really loud
(fortunately there weren't any kids around!) and went home and ordered a new helmet!