I have not had positive results with a Kaweco mini converter.
Even their international-fit Kaweco-branded converters, for their longer pens (Dia2, Kaweco Special FP.....) have leakage problems, bubbles, at least with me. (I've switched to a Visconti converter in a long Kaweco Pen)
But, the Brass Sport is a relatively short pen which would work best with International short carts of your choice, even refilled ones.
Wow , I just wanted to post a quick update , perhaps an amendment to what I said above.
So, I clicked onto the next two pages of this interesting thread, at least I "tried" to read the pages that filled up since I first wrote. After a loooooooong wait the second page popped in. Such dense, detailed content. To get to page three, some more waiting & more fascinating content to read & look at.
My update here is not exactly about the original question about a mini squeeze converter to fit a Kaweco. I stand by what I said about Kaweco's mini-piston & mini-bulb converter, that the design is still a work in progress. For the modern small-sized Kaweco pens I just use international carts. For colours there are lots of options, particularly from Diamine. For me, good old Pelikan 4001 blue/black suffices as the standard. This (rather dull) colour can be sourced through the UK.
Now the good news: ......my Kaweco-branded large piston converter "suddenly" started working perfecly (the way I'm sure the manufacturer intended) after I installed it into one of my slim Kaweco "Special" FP pens. When I plugged the converter in , it must have formed a close to perfect seal because the piston was now actually raising quite a good column of ink with very few bubbles, & on the first stroke. (I usually fill with three stokes + 2 drops + pull back the plunger, then wipe.)
By the time I cycled the converter with ink for the second time, its tube was completely filled. I decided to use a mild iron-gall ink like Platinum blue/black. This Kaweco-branded converter worked just as well as my trusty Schmidt K5s used to. All this winter I filled this same pen+ converter combo with a whole variety of ferrogallic inks, flushed & dried the pen each time in between fills,...no issues, just happy writing.
Although Visconti's converter made a solid connection into my Special's section, but its tube would not fit into the narrow tube that forms the pen's barrel.
Kaweco's own converter has such a close fit in the Special's slim barrel that there is non of the rattle that you sometimes get with other pen & converter combinations. This converter seems a winner with my Kaweco Specials.
Yet, when I installed the same Kaweco piston converter into my old Kaweco Dia2 pens, there seemed to be poor sealing at the nipple, resulting in a tube full of bubbles, almost no suction,...the converters seemed useless.
I dedicated my Dia2s for use with just international cartridges, but that was limiting. They were otherwise great pens, though I passed on both the pens to new users.
So, now I revise what I said about the Kaweco-branded large (clear plastic) converter with a metallic silver ring at its mouth. It works the way it should. My troubles with this Kaweco accessory may have been operator error on my part.
Edited by tinta, 26 July 2019 - 23:48.
*Sailor 1911-M, Black/gold, 14c. 0.8 mm. stub(JM)
*2 Sailor 1911-M Burgundy/gold pens: 14c. 0.6 mm. "round-nosed" CI (MM) & 1.1 mm. CI (JM)
*Sailor Standard sized Brown Marbled Mozaique,(machined acrylic/rhodium),14c. 1.0 mm.CI (JM)
*2 Kaweco SPECIAL fountain pens: 14c."M" "B",-0.5 mm & 0.7 mm (BLS)
*Kaweco Stainless Steel Lilliput, 14c "B" -0.6 mm. (BLS)
*Montblanc 254, 14c. "BB" (1.1 mm?) flügelfeder factory stub