FWIW, a relief hole just drilled it diametrically at the top of the bore helps a LOT, but one drilled at about a 45-degree angle from vertical (high on the outside of the rod, lowest where it intersects the bore) will do a lot more to keep the bore of the rod clean.
With the angled hole (larger than the pintle bore), any powder forced up into the relief tends to remain loose, rather than being compacted. It then usually tends to just drop back out when the rod is removed from the mold.
We pressed dozens of different tube-items at the shop, including some 'cored' devices, like what are being discussed. The angled hole allowed some of that to be automated with NO (zero!) failures due to the press-rod clogging-up. We had a very few damaged core pintles (but no explosions, thank goodness!) when we were using a diametral hole, which is why we changed to the angled one.
Edited by lloyd, 09 February 2017 - 10:57 AM.