Thanks for doing that. I've found some MG Chemicals 63/37 0.032 and was just about to buy and then noticed that that solder in the examples doesn't seem to have fully flowed over the pins. Or is it just my eyes ?
Flow itself looks good to me.
MG Chemicals makes good flux and solder IME (on equal footing with Kester, Multicore, AIM, and so on). They don't offer as many variations as other manufacturers though. Even Multicore has cut back on their lead alloy offerings.
If you can find it, AIM (American Iron & Metals) or Alpha (Cookson) make some excellent quality products as well, and at least here in the US, tend to be a tad less expensive vs. Kester.
You are right, the Oatey IS Sn40/Pb60, you can see it on the label (now that I think of it I have no clue where it came from :-). Given that the Chinese solder looks similar and clearly says 63Sn/37Pb what does that mean? As I said before I've tried similar solder from EBay with similar results. Might be worth buying more samples to see if it's a common rip-off.
I thought that was the case from what I saw in the photo, but couldn't be sure. And the appearance is far too similar between the cheap Chinese sourced solder and the Oatey to be a coincidence IMHO, but held off making a comment until I was sure on the Oatey's actual alloy.
As per why this could happen, the position of Sn and Pb can be either way; electronics tends to go Sn followed by Pb, but it seems the position of the metals used is not universal. So I could see how that could get Sn60/Pb40 swapped with Sn40/Pb60 (possibly by mistake)
That said, it's far more likely based on greed IMHO, as tin (Sn) is more expensive than lead (Pb). Now take it a step further; "60/40 is close enough to 63/37" in terms of where the numbers for the alloy fall, and less scrupulous vendors slap both labels on a single alloy (further increase their profits on the 63/37 labeled rolls they ship). So put both together, and voila; you get Sn40/Pb60 with a Sn63/Pb37 label slapped on it. All done to fulfill the goal of lining one's pockets as quickly as possible, ethics be damned.
It's probably just my crappy soldering
Yes it is.
For prototyping, what you've done with the quality solder samples is sufficient IMHO. My one suggestion, cut back on your solder a bit so you form a fillet in the joint (curve between the solder on the pad and where it makes contact with the wire lead). Also keep the iron in contact with the pin/lead as you remove the iron (this is what pulls solder up the entire lead; goal is to have solder covering all of the lead, including the end where it's trimmed off).
Plenty of free resources that have photos or illustrations of what this is might help (covers other stuff that might be useful).
You don't need to be able to meet NASA/mil-spec/avionics standards, but if you can manage say 80%, you're doing extremely well (focus on the joint appearance; you can skip the "clean solder wire of oxide with alcohol soaked Kim wipe before soldering" types of steps). Necessary for their particular applications as a CYA, but not necessary for bench use/consumer products.