when i think of a buckler i think of something you use in your hand. anything that straps to your forearm would have to be big enough to at least cover your wrist, and by that point i think it's a shield.
No, it wouldn't have to cover the wrist. It can be stablized in one of several ways.
One, is to affix it to a gauntlet/glove. It then moves as the hand does.
The second is to have it back far enough to cover the elbow, using the upper arm to stabilize it.
The third is simply to strap it tightly to a vambrace. Less comfortable.
It can extend past the wrist, and have the second (or third) strap be across the palm, like is done with a targe.
From inside of elbow to crease of wrist, my forearm measures 9" or so.
My 12" targe doesn't protect my elbow, which means I cannot use standard shield techniques with it; when worn, it's about 1/2" past my knuckles, and as padded, if I extend my fingers, the rim just touches my 1st knuckle on each finger.
I can use only slightly modified buckler techniques with my targe.
Now, I've used 10" & 15" leather bucklers, and 15" steel bucklers, as well as full (2.5x3') heater and 3'x3' lozenge, a 24" viking round, as well as a my 12", and others' 24", 30" and 36" targes in various SCA and reenactment activities. A small targe doesn't work like a large one. Unless it covers wrist and elbow, many of the shield techniques simply do not work well, and the passive protection simply isn't enough to equal a full sized shield, either.
A small targe is neither shield nor buckler, but somewhere in between; it's a parrying tool, more than a blocking tool. More agile than a full sized shield, and more firmly strapped on than the hand-held-only buckler.
