First, Bruce Gray of GrayGuns says so and his testing has supported his reasoning.

Plus there's the theoretical, mathematical limitations to consider. I know people tend to discredit math and theory, but math and theory put men on the moon and brought them back. Granted, math can't account for everything, because some things just can't be accurately, mathematically modeled - such as the human body. But a gun is not a human body. It is in fact a pretty simple, structured dynamic device and math can be applied to help us understand theoretical limits to complex mechanical system with a high degree of accuracy.

Computer modeling of complex mechanical systems is pure mathematics. Sooo...

Let's set the conditions. a P226 compared to a Glock 17. Even thought they're not, let's assume both are manufactured to the exact same slide to frame tolerance of 0.01". That's pretty tight but we can plug in whatever number you feel is most accurate. For the sake of discussion and simplicity, we will assume the barrel to slide lock up is essentially zero tolerance. We will assume a perfect sight picture, and lastly we must assume the shooter, whatever he or it is, will not disturb the sight picture in the process of shooting.

Let's do some math. Let's calculate the theoretical inherent accuracy of a P226 with 6.25" rail lengths and a G17 with 4.75" rail separation. It doesn't matter that the rails are not continuous.

We will look at the worst case misalignment due to the tolerance of the slide to frame fit. This will apply whether we consider vertical or horizontal play. The worst error will occur when the slide travels as far as it can at the rear and as far as it can in the opposite direction at the front.

The error at 50 yards would be given by,

error = 50 yards x 3 x 12 x tolerance / frame rail length

where, 3 converts yards to feet and 12 converts feet to inches so the units all match, and the tolerance is 0.01" as set earlier.

For the P226,

Error = 50 x 3 x 12 x 0.01" / 6.25" = 2.88"

For the G17,

Error = 50 x 3 x 12 x 0.01 / 4.75" = 3.8 inches

So how does that fit with reality? Well, quoting Bruce Gray,

"...Such a fit in a conventional P-series should buy us 2.5" at fifty yards or so..."How close is that! But he goes on to say,"I have shot some Glocks, XD's and so forth, and have yet to see either pistol consistently produce sub-5" 50 yard groups in factory trim, and often not a whole lot better than 3.5" to 4" when re-fitted or re-barreled.how close is that!

I should make this really clear, Bruce was not referring necessarily to a 0.01" tolerance. I picked that because I believe that could be realized in high quality guns. We see this same full length rail demonstrated again in 1911s that can be very precision fit and have long rails to boot. Of the 1911, Bruce says,"My personal 1911 is giving me well under 2" as expected, so at least I know I can still shoot a group!"Remember, that's at 50 yards!

However out of the box accuracy of polymer guns, according to Bruce, is about 5" at 50 yards. He believes some of that is due to frame flex. The P250 he's been playing with is getting 4.5".

So what does all this mean? Well, for one thing, it means metal frame guns will have more inherent accuracy than polymer guns of similar size.

Second, it means most guns are sufficiently accurate for all but the most demanding applications, like the Bianchi Cup.

Thirdly, it means most of us can't shoot well enough for the inherent accuracy of the gun to be significant.

Fourth it means other factors such as sights will play more of a part in accuracy or inaccuracy than inherent accuracy will.

Fifth, contrary to a general attitude toward theory and mathematics, the real world results and theoretical results agree amazingly well!