Why I believe polymer guns can never be as accurate as metal frame guns

This is a discussion on Why I believe polymer guns can never be as accurate as metal frame guns within the Defensive Carry Guns forums, part of the Defensive Carry Discussions category; 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 ...

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Thread: Why I believe polymer guns can never be as accurate as metal frame guns

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    Why I believe polymer guns can never be as accurate as metal frame guns

    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!
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    Member Array Biggie313's Avatar
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    I am not seeing how a slight shift in the frame and slide makes a difference. The barrel is attached to the slide, and so are the sights, so if its .01 off, when you line up your sights 100% correct, that is corrected. The barrel will be pointed straight, the frame maybe be off by that .01, but that doesnt matter. the frame doesnt come into play until after the bullet has left the barrel

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    I fit right about... here.

    Quote Originally Posted by Tangle View Post
    Thirdly, it means most of us can't shoot well enough for the inherent accuracy of the gun to be significant.
    Of course, we could think about making guns out of more expensive and rigid metals than steel or aluminum, and then plate them with even more expensive stiffer metals... You could end up with a nice and accurate $$$$$$$ expensive custom handgun. Are there any out there, like this?

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    Leave it to you to come out with this, lol. However, I see the logic and agree that the mechanical accuracy of a metal frame will be more accurate.

    Of course, like you stated, most shooters will never realize the mechanical accuracy.

    Then again, there is accuracy, and practical accuracy.

    And of course, there is the theology that there is a trade off in inherent reliability in the choices. I guess a guy or gal just have to make a choice. Good post, partner, informative, and logical.

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    los
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    Basically, the theory is that in a controlled testing environment, at 50 yards a Sig P226 (with a 6.25" rail) should theoretically exhibit more accuracy than a G17 (with a 4.75" rail) by about 0.92"?
    What we've got here is failure to communicate.

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    I always thought the majority of accuracy came form the tighter barrel lockup regardless of the frame...
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    I believe it's the flexing of the polymer frame at the end of the slide cycle that is the differene in altering the POI consistency.

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    los
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    Quote Originally Posted by glockman10mm View Post
    I believe it's the flexing of the polymer frame at the end of the slide cycle that is the differene in altering the POI consistency.
    The bullet has probably already hit it's target way before complete slide cycle takes place.
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    What we've got here is failure to communicate.

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    Does the difference in length of the frame not come into play? Are there any other factors that affect pure mechanical accuracy in this case? (All factors should be considered, and each isolated for examination, should they not?) If the gun weren't locked in a vise and mechanically triggered for the tests, can we take the shooter enough out of the 'equation' for the results to be useful?
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    Quote Originally Posted by Biggie313 View Post
    I am not seeing how a slight shift in the frame and slide makes a difference. The barrel is attached to the slide, and so are the sights, so if its .01 off, when you line up your sights 100% correct, that is corrected. The barrel will be pointed straight, the frame maybe be off by that .01, but that doesnt matter. the frame doesnt come into play until after the bullet has left the barrel
    Ahhh, I see the confusion. The assumption is the barrel and slide are locked up tight, no play or motion between them. Hence the barrel, slide, and sights are all aligned and can't move. However, the slide and frame are not locked up tight and the slide can move around on the frame a bit. If the sights are perfectly on target, and the shot breaks, I'm assuming the frame remains completely stationary as in a immoveable rest.

    Since we would be considering a human hand holding the gun, such as Bruce, I'm assuming the slide will move before the frame does and hence the misalignment. I have to think that's a pretty sound assumption since the rigidity of the two hand hold, the mass of the frame and the mass of the hands will have less motion than the slide which has a direct reaction to the bullet accelerating down the barrel.
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    Quote Originally Posted by los View Post
    The bullet has probably already hit it's target way before complete slide cycle takes place.
    Probably true, but we're not talking about a slide cycle, we're talking about a movement of 0.01". If the slide to frame fit had no impact on accuracy then a very loose gun would be just as accurate as tight gun.
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    Regardless of type frame, few (if any) of us will ever overcome the human factor to the extent that the slight mechanical differences make any sufficient difference in bullet-on-target accuracy.
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    Quote Originally Posted by CR Williams View Post
    Does the difference in length of the frame not come into play?
    Yes and no. A Sig 226 has a longer frame than a Sig 229 and since both have full length frame rails and the P226 is longer then, given the same tolerances, the P226 would be more accurate. However the G17 is a significantly longer frame than a Sig P229, but the P229 has longer rails so the P229 should have more inherent accuracy based on frame rail length.

    Quote Originally Posted by CR Williams View Post
    ...Are there any other factors that affect pure mechanical accuracy in this case? (All factors should be considered, and each isolated for examination, should they not?)
    Not any that I can think of. Once the shot breaks, the trigger and just about all other components other than the slide to frame fit and barrel to slide fit is out of the picture.

    Quote Originally Posted by CR Williams View Post
    ...If the gun weren't locked in a vise and mechanically triggered for the tests, can we take the shooter enough out of the 'equation' for the results to be useful?
    The shooter doesn't contribute anything to inherent accuracy. If we include the shooter, the total error will be the inherent accuracy of the gun plus shooter's ability. Inherent accuracy is the 'built-in' accuracy of the gun.

    Glockman10mm referred to 'accuracy and practical accuracy'. I presume he was referring to what the human can do would be practical accuracy.
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    Quote Originally Posted by los View Post
    Basically, the theory is that in a controlled testing environment, at 50 yards a Sig P226 (with a 6.25" rail) should theoretically exhibit more accuracy than a G17 (with a 4.75" rail) by about 0.92"?
    That's the way I see it, and Bruce Gray has the skill to demonstrate it - and I'm green with envy!
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    Quote Originally Posted by OldVet View Post
    Regardless of type frame, few (if any) of us will ever overcome the human factor to the extent that the slight mechanical differences make any sufficient difference in bullet-on-target accuracy.
    Yes, Bruce Gray can for one and many Bullseyes shooters for another. In fact, it is the inherent accuracy of polymer guns that Bruce says limits their out of the box accuracy to 5" at 50 yards. Yet he can take a P226 and get close to 3" groups.
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