the pogo pins have replaceable contacts (they are a sleeve and a pin) so thats the only reason why i gravitate to them, plus it probably slightly hardened and gold plated.
If you do use pins, be aware my half finished one in the vise is a pain in the ass to load, since I do not have a external big spring, I need to position the part in tweezers then use another pair of tweezers to separate the pogo pin and slowly push it back into place. It is annoying and a few parts were shot away from me. I thought about making a little pedestal out of some material to rest the part on on top of a screw to adjust the height but I am not sure what the screw should be made of, and it seems unnecessary unless i widen it alot to fit a big inductor or something.
A big external spring mechanism is superior so long the RF parameters are OK. I don't have the tools to make a nice joint (I do have a brass surface grinder sharpener fixture that I will likely never have a surface grinder for,which is almost perfect to modify because it has a smooth travel in a long piece of brass, but i also thought to just make an attachment to use that to dress my bench grinding wheels so its probobly better to leave that tool alone). Since I got some beryllium spring copper i will experiment with making springs, I don't have a knack for figuring out what kind of spring I need to get the mechanics right or the tools to make it operate smoothly. Maybe I will try to make a little one built like a watchmakers vise on my proxxon mini mill or modify a watchmakers vise (the one for holding the bowl part).
My current fixture has a discontinuity in the dielectric, I cut it as flush as I could with a razor to expose a piece of center conductor so I can solder the pin holder in the brass tube to it, then slid another piece of dielectric on and soldered the brass tube on top. However if you have the N connectors you can probobly solder the center conductor to the coaxial connector pin and the pogo extension and slide a single piece of dielectric back over that and solder the N connector over that single piece. I am not sure what that thin discontinuity does from razor cut, a TDR would tell me nicely, but I have a feeling it does not matter much at only 300MHz max. I have materials to try to make non interrupted ones if I get access to higher speeds but its already pretty interesting.
I got the aluminum solder to work alot better by using it alone for the joint instead of pretinning, to use my regular soldering iron with the special acid flux and clean it afterwards with mild abrasives and solder it like a normal solder joint, and to really scrub the aluminum solder down with stainless steel wool in soap water prior to soldering and cleaning with alcohol. It is actually more difficult to join the pretinned surfaces then just flowing a normal joint, I think the problems I was having was just really nasty solder, from my brazing drawer in the tool box, in the uncontrolled garage.. I had to throw out all my RG45 rods from corrosion and spent like 2 hours fixing the brass rods filler on the buffing wheel lol. I stopped trying to get the joint the right size and instead overfill it so there is a big bead and then use a dremel sanding drum to get it back into a cylinder shape then polish it from 120 to 2000 grit with the plastic radial disks along the entire splice before sliding the sleeve on top to reduce insertion force. The only problem my current fixture has is that one side needs to be rotated to get the pogo pins to make good contact (it is slightly off center because when I was soldering the pogo pin sleeve into the brass tube I did not have a nice centering fixture for it, I got lucky with one being dead center and the other one is sensitive to rotation or its misaligned. I also don't have whatever N connectors were used with the factory cable I modified, so one of my connectors is a right angle one, but it ends up working because I run the fixture ontop of the VNA when its inside of 19'' rack, next to the other rack, so I will probobly leave it alone for now. Anyway I am excited to see it worked and eventually I will do the refinements.
I am also going to solder some of those micro alligator clips to the end of some pogo pins so I can put alligator clips inside of the fixture to test small leaded parts, those small copper alligator clips can be bent easily to conform around different diameter leads. Since they are replaceable its cool because you can solder stuff directly to the pogo pins and insert them into the fixture, and even seize the pins with solder to get rid of the spring action in such situations, so it makes a micro pin connector. You can even solder them to empty PCBs without coaxial connectors to make boards that slide into the gold sleeves, so long its acceptable the board is floating from ground, which still may be useful for testing series components chains.