Roman crossbow

[Thomas V.]

[C]onsidering Bone Nuts survive, then the Lathes of a Composite bow would have also survived in those cases. This indicates at least the 3 finds in Britain may have used self-bows.

It could also indicate that the nuts stem from a period for wich the use of self bows for crossbows is attested (i.e. post-Roman times). The possibility that the two or three other nuts might be stray finds could also be an explanation for the nuts not having been found in conjunction with bone/antler reinforcements.

Indeed a Self-Bow can be powerful enough, as 4-foot Native American Selfbows can draw 50 pounds at 2 feet.

Are said bows self bows or bows with a sinew backing?

Climate is the key element that affects of materials to build bows. It would be pointless to use composite bows in Britain since it's humid air quickly dissolves glue of composite bows eventually causing it to collapse. Simply, Roman craftsman were aware of this and they could had chosen self bows for Britain.

Parts of composite bows were found in Britain; said parts where found in a Roman context. So the Romans seemed to use composite bows in Britain.

[L]ooks like a composite built bow.

It really looks like a composite bow: Set back handle and tips pointing forward when the bow is unstrung.