I have a number of high spine carbon field archery arrows that are now too short for me. Is there a way bodging a set of poles using standard pile inserts and a suitably threaded jointing piece? I have some blunts that will do as feet.

You may find they're too flexy once a reasonable length. 5/16" I assume?

300 spine though

All you can really do is try it. For joining them together, I'd be tempted to try and find something with an ID of the shafts OD and make external spigots.

See if I can do it ready for bb200

Eventually got round to it.

320 spine heavy hunters. Used long inserts with the end cut off glued half in as the joining piece

Quite stable in the back garden with a shaped tarp

Cut to 10" lengths. Used protector rings so they won't split. Rubber blunt end to stop them ripping the fabric

4 lengths for the front, 2 for the feet, surprised how well it works

Just over 100g