Heat Matched Darts with CPVC

Following a post by Burr on NH I tried heating some cpvc barrel material with a common coffee warmer instead of metal on a cooktop.  I had some (19!) barrels cut to 2 1/2" for an absolver. There's a rubber band holding them together. The warmer is not a particularly powerful one. I tried mine on high and it deformed a few barrels so I would stick to low at first. In usage I found it best to load it with darts (to about 1/4" of the bottom) and then place it on the warmer for 15 - 20 minutes (longer for stock darts). It's hard to gauge but my darts melted a bit at the bottom when they were done. A little less gets a tighter dart but over 25 minutes started to deform the surface of the foam.

 The fit I got with stefans and 25 minutes was a loose airgun fit. In petg it would need tightening rings. At 15 a springer fit seemed usual. It's not fully consistent with the darts in the center getting a bit hotter sometimes perhaps.

Here's some stock darts I ran through. They fit into cpvc much easier and seem to keep their size well.

Once the barrels cool down the darts are easily pushed out or removed. I found it important not to twist stock darts in lest they wind up crooked after cooling.