Golden guns were 300 points to buy and it looks like you get 1 point per win, so need to win 300 matches each weapon. Winning more = faster purchases!
If the formula is anything like LoL, the first match(es) are much more heavily weighted than the latter matches. Placements is a method to get you where you belong aggressively. So the very first placement match is worth more than the 2nd which is more than the 3rd, etc...
Since I started 0-2 I probably lost more rating than what I gained during my last few wins (matches 7/8/9/10). If you start out with a few wins but lose later, it won't be as punishing.
So 3 of us so far claimed to have a 7-3 record.
Mine: L-L-W-L-W-W-W-W-W-W : Result 48
Cinge: ?-?-?-?-?-?-?-?-?-? : Result 54
Valorath ?-?-?-?-?-?-?-?-L-L : Result 50
Another factor is I'm fairly sure they take into account your QP MMR when matching 1st placement match. LoL does same thing, and it explains why the pros end up in the 70s after placements, even when not going 10-0.