What was the OEM capacity on 59 mags?
I picked one up somewhere--well, figured it was a 59 mag, "lazy &"
between S and W on floorplate--and it holds 15. It
has no indents at lower end of tube.
The 59 mag appears dimensionally identical to
a Beretta "92 series" mag, which hold 15.
The Model 59 and 459/559/659 came with 14 round mags with a stamped steel magazine base. Third gen 59xx pistols came with a 15 round magazine that had a plastic base plate. Internally, the difference is the follower. Putting a 59xx follower into a first or second gen 14 round magazine will give you a 15 round magazine.