My wire tables say AWG 40 is 33,410 ft/lb.

So, for 250g =0.551155655 lb would be 18,414 ft = 5,600m, about 4.6x

as long.

The reason for the discrepancy-- the diameter of AWG 40 is given as

3.145 mils or about 0.08mm. Square the ratio and we have the

difference accounted for.

Or, to put it another way, how long is a piece of metal string? >

What with the differing vlues for density, the unknown thickness and weight

of enamelling, and what may or may not be a confusion somewhere between

radius and diameter, the room for error is large. The OP gives 0.17 mm as a

diameter, but yours might be a radius, given a figure of 0.08. I've no idea

which is right, but that half/double between the two values is suggestive.