I have tried both molds and here are my observations on both.
Molds with built in stoppers:
PRO's Can get molds made with several different pen styles in one mold.
The sides did not seem to press in on the ends of the tubes when casting under
pressure.
CON's You have to have a mold for each size pen, ie if you cast Sierra and Aero you need
a mold for each.
Many tube leaks casting under pressure with no way to make the seal better. I had a
4 different pen mold, hold 8 tubes at a time. Of these 5 of tubes leaked at any
Pressure over 25 psi.
The built in plugs break easily and are hard to repair.
Molds with separate stoppers:
PRO's a single mold can be used for pen where the tube diameter and length are close. One
Mold can work for both a Sierra and an Aero, a Jr Gent and a Triton, a Gent and an
Imperial.
With the tapered stoppers have not had any tube leaks when casting under pressure
@ 50 psi
If a stopper goes bad they are cheap to replace.
CON's The end of the molds have a tendency to push in on the end of the tubes when
casting under pressure.
My preference is for the mold with separate stoppers. No tube leaks and the ability to cast different pen styles in the same mold are the biggest factors.
Mike