In the semiautomatic pistol pattern pioneered by John Moses Browning, of the reciprocating slide carrying the sights and enclosing a (fixed or tilting) barrel, the consistency of barrel alignment in battery, to the sights mounted on the slide, is the single most crucial factor in determining practical handgun accuracy. Since in the M1911 design, the slide requires a removable bushing, its muzzle end barrel play can be readily controlled by hand fitting this part to minimal tolerances. Similarly, fitting the appropriately sized swinging link that controls the travel of the barrel through the recoil cycle enables the M1911 to be tuned for maximum precision of breech lockup to the slide lugs. But the extra clearances between the slide and the bushing and those between the swinging link and its pins adversely affect the consistency of barrel alignment to the slide.
These considerations motivated the development of the Colt Series 70 collet bushing design, which controlled the muzzle end of the barrel with self-sprung fingers. Unfortunately, it was plagued by breakage issues. Today, a similar effect might be achieved with spherical barrel bushings pioneered by Briley and popularized by Smith and Wesson, or flared bull barrels fitted directly to bushingless slides.
The problem of extra clearances was solved more definitively in the final pistol design to incorporate Browning’s contribution, the Hi-Power or Grand Puissance (GP), completed by the FN engineer Dieudonné Saive, later renowned for work on the FN FAL. Saive superseded the M1911 removable spare part with a bushing permanently pinned into the slide. The GP35 also dispensed with the pivoting barrel link used to tilt the barrel in the recoil stroke of the M1911 in favor of a camlock ramp bearing against a steel lug staked into the frame. Most subsequent Browning pattern pistol designs incorporated both of these features.
The
SIG P210 was a considerable refinement of the Browning design, as it had been further developed by Saive, Fedor Tokarev, and Charles Petter. Whereas the bushing fixing the barrel at the muzzle end and the link controlling its travel through the recoil cycle enabled the M1911 to be tuned for maximum precision of barrel lockup to the slide, the integral slide and barrel cam on the P210 achieved better lockup consistency in forgoing the flexibility by dispensing with these extra parts.
The P210 is sometimes acclaimed for making a design contribution in its inverted slide rail arrangement. But this ostensibly novel arrangement duplicates the receiver to frame interface of the previous Swiss service pistol, the Georg Luger-designed Parabellum, equally known for its superlative accuracy. The M1911 slide rails face outwards of the frame. The GP35 improves on this by having two sets of rails, the inner and the outer. Given equal clearances, the end-to-end length of slide rails is the most important factor in the alignment of the slide to the frame. In the final version of the GP35, Saive nearly doubled the slide-to-frame engagement of the M1911. The P210 design has nearly twice the rail engagement of the GP35. Thanks to this feature, the Swiss pistol combines superior slide alignment with sufficient working clearances.
Mechanical accuracy, as measured by groups shot out of a machine rest, is greatly improved by the inverted rail design of the P210 enabling more precise and durable slide to frame alignment. Correlatively, practical accuracy is aided by making the trigger action on the P210, as determined by the sear engagement within the field replaceable unit construction hammer assembly, far easier to tune and maintain. Acting together, these refinements are responsible for the superior long-range performance of the P210.