The SIG P210 design is a licensed evolution of the 1935 S Petter pistol, in turn inspired by the Tokarev TT30, which at first was faithfully scaled up to 9x19mm Luger from the French chambering in 7.65x22mm Longue. Its additional design influence came from the Radom Vis wz. 1935, developed by Piotr Wilniewczyc and Jan Skrzypinski. Its main competitor was the Browning-Saive GP35 derivative, W+F 43 and W+F 47.
On 19 May 1942, SIG tested five contemporaneous service handguns for accuracy in preparation for the development of their candidate for the next Swiss service sidearm, eventually adopted as the Pistole 49 and designated commercially as the P210. This is what they got in 8 shots fired at 50 meters:
Walther P38:
12.0cm from rest/14.5 cm offhand
Radom ViS35:
18.5cm from rest/17.0 cm offhand
Colt M1911:
30.0cm from rest/42.0 cm offhand
9mm Luger 06/29:
5.5cm from rest/11.5 cm offhand
7.65 Luger 06/29:
5.8cm from rest/9.0 cm offhand
The test Colt was a 1919 commercial Government Model, SN C113936. (See Armbruster, p. 15.)
In developing their improved version of the tilting barrel, short recoil locked breech autopistol design pioneered by Browning, Tokarev, and Petter, SIG engineers aimed at improving the performance of the M1911 at 50 meters sixfold, shrinking its 30.0cm 8 shot groups obtained in their machine rest tests, to less than 5cm, without compromising its ruggedness or reliability. To that end, they reversed the customary rail interface between the slide and frame from its prototype designed by Browning and patented by him as U.S. Patent 580924. Whereas previous slides incorporated rails that aimed inward, towards each other, and reciprocated on tracks cut into the frame, the slide of the P210 mimicked the arrangement of the Luger receiver that reciprocated within the frame. As with the Luger, the P210 frame tracks were located on the inside, whereas its slide rails faced outwards, away from each other. SIG designers also dispensed with the barrel bushing, as used by all three of their predecessors, Browning, Tokarev, and Petter. In its stead they used a solid slide with a differentially bored opening at the business end, allowing the barrel to drop down at the breech while minimizing play at the muzzle.
References:
Erwin Armbruster & Werner Kessler, Begegnungen mit einer Legende — SIG SP 47/8 / P 210, Kessler Waffen AG, 2007
Lorenz Vetter, Das grosse Buch der SIG-Pistolen, Motorbuch Verlag/Verlag Stocker-Schmid, 1995, ISBN 3-7276-7123-8
H.P. Doebeli, Die SIG Pistolen, Motorbuch Verlag, 1981, ISBN 3-87943-739-4