Location: South Bay
|For a butt that size, you can try a solid hardwood dowel that is tapered to slide in the inside diameter from the bottom. That's unless you have access to a thick wall sacrificial butt section off of another older rod that will fit inside as well and are willing to cut a section off that fits.
Basically, you need to measure and test carefully so that at least 6 inches of the dowel is tapered and inserted firmly into the butt section with no play and still long enough for your extension. To get the taper, measure with calipers approx wall thickness and the change in outside diameter over the inserted length.
Don't jam it in just yet. Do gentle press fit for now and when you think you've got the right section and taper for fit, then remove the dowel and wrap the butt section in heavy guage thread, double layer, then seal, let dry, and epoxy over to make a ferrule and let harden overnight. Use generous epoxy resin this time and spread on dowel and inside ferrule, and then slide and twist dowel into ferrule and then let harden while keeping rod vertical with butt section down.
If you're really hard core, and went to a good autobody store or hobby store and have fibreglass cloth and resin, mix a batch up and slather over the new butt section and on to the top original shaft. wrap tightly a good 4 - 5 layers of fibre glass with resin and let dry and then sand a bit.
Now your butt section should be extended and you just need to put on the right butt cap and wrap and you should have an extended handle.
Yes, I can roll potsticker skins!