I know that the West Systems 610 has been suggested as replacement. Other than it coming in bit smaller packaging and needing a caulk gun, it seems decent.
Its not quite as thick as either Rocketpoxy or ES3629 to me. But it went on as a filet quite well and is holding its shape, so thats good. However I did notice that it has lots of bubbles. Being quite clear, compared to ES3629 or RP with their fillers, its quite easy to see them.
I did three de-gassing passes with a vacuum pot, but still have issues with bubbles.
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Again being clearish, you can see the bubbles. I worked it pretty hard to avoid bigger bubbles when applying and smoothing the epoxy.
610 might be useful for some smaller mid and low end high power rockets for me. Think I'll go with the ES6279 for larger rockets at least until I try some Proline 4500 myself.