I had blowouts on my early pens, which were glued with medium StickFast CA glue. Here are some things I learned that may help you.
* It depends on the wood. What type of wood is @Phixius using? I have trouble with more blowouts from "brittle" woods like marblewood, for example. It blows out more than other wood types that I have turned. Other woods might soak up a lot of the CA, leaving too little glue between the tube and the blank. A book I read on pen turning suggested that you apply thin CA to the inside of the hole on certain "absorbent" woods before gluing.
* Use "Flexible CA" for glueing tubes. CA can be brittle when cured. Flexible CA has some "give" and that extra cushioning and flexibility may help keep the wood attached to the tube, where a regular CA might crack apart.
* Glue application technique? It sounds like Phixius is doing all the right things, making sure that the glue is thoroughly distributed between all of the tube and the inside of the blank.
* Use activator? When I was having blowout problems, my expert pen turning friends suggested spraying activator on each end of the blank after the tube has been inserted in the blank. That helped. The blowouts stopped, but it could have been improved technique or other factors.
* Old glue? Glue I bought mid-summer 2018 has not worked well for CA finishes for the last two months. Replacing with fresh glue fixed the problem instantly.
* Frankly, the best answer for me was that I switched to polyurethane glue for most pen glue-ups. I have never had a blowup or other issue with polyurethane. See my notes below.
When I Glue Tubes with Something Other than Polyurethane:
* Flexible CA Glue: If I do not have time to wait overnight for polyurethane glue to cure, then I use flexible CA glue. Sometimes you want to make a pen from start to finish in one session. Once the tube is inserted in the blank, I spray each end of the blank with activator, per my friends' recommendation. The blank(s) should be ready to turn in a few minutes.
* Epoxy: I use epoxy on special pen blanks where the glue might show, like those translucent acrylic pen blanks. (I used to paint the tubes but not the holes. The next pen, I plan to paint both, and will reassess to see if I still need epoxy in those cases.)
Polyurethane Glue Notes
If you are thinking about switching to polyurethane, here are a few hints:
* I dip a Q-tip in water and wet the inside of the drill hole before glueing. The water helps activate the polyurethane glue.
* I wear gloves and work on a Rockler silicone mat and wax paper. Polyurethane is messy.
* I squirt polyurethane glue around the tip of the tube and spiral it along the length, then I insert the tube with a twisting motion, pulling it in and out while twirling, to make sure that the tube is fully coated.
* During the next hour or so, the polyurethane will foam out of the hole and down the outside of the blank as it cures. Let your blanks cure on wax paper or a silicone mat. I have never seen it happen, but I have been told that it can push your tube out of the hole.
* I use a sharp chisel to slice off the excess polyurethane from the outside of the blank. There is no use dulling your pen mill on hard glue. Chisels are sharp. Be careful!
I have tried using Play-Doh to plug the tubes before glueing. It was messier and more work than cleaning excess glue with the pen mill (or on rare occasions, a round file). I have not tried potato or dental wax yet. Frankly, glue cleanup has not been much of an issue for me.
I hope this helps.