Question for the Engineers & Scientists ?

This is a discussion on Question for the Engineers & Scientists ? within the Defensive Carry Guns forums, part of the Defensive Carry Discussions category; There are frequent posts about the "break-in period" for new semi-automatic handguns. Most wonder about how many fired rounds predict reliability. A worthwhile question, since ...

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    Member Array gold40's Avatar
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    Question for the Engineers & Scientists ?

    There are frequent posts about the "break-in period" for new semi-automatic handguns. Most wonder about how many fired rounds predict reliability. A worthwhile question, since one's life may be involved.

    From a PURELY STATISTICAL STANDPOINT (and I barely passed my college statistics course several decades ago) is there an answer?

    If a brand new semi-automatic handgun, properly cleaned and lubricated, using fresh quality ammunition, fired the first 15 shots without any malfunction, what is the statistical probability it will fire the next 15 shots without malfunction?

    Does that probability increase significantly if it fires the first 100 shots without malfunction. If so, how much?

    If it isn't too complex, please show us the formula....

    THANKS.

    JERRY

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    Senior Member Array highvoltage's Avatar
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    Simplistic probability dictates that the probability of the first 15 rounds fired is 1 (P(fire) = 15/15 = 1). Given there are no other factors influencing the outcome then the probability of the next fifteen rounds firing would also be one (P(fire) = 30/30 = 1)

    At this point your probability can't increase, it can only go down. If your first 100 shots are fired without incident, they you're still at 1. If however, you have a misfire somewhere in the next 100 rounds, then your probability is now P(fire) = 199/200 = .995 Now from here it can go up. For example if you fire the last 800 rounds without incident they your final probability for 1000 rounds is P(fire) = 999/1000 = .999

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    Senior Member Array dV8r's Avatar
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    I like simple.
    The next logical step would be to break this down by ammunition type and individual magazine.
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    Voltage & Wattage are different <g>

    Quote Originally Posted by highvoltage View Post
    Simplistic probability dictates that the probability of the first 15 rounds fired is 1 (P(fire) = 15/15 = 1). Given there are no other factors influencing the outcome then the probability of the next fifteen rounds firing would also be one (P(fire) = 30/30 = 1)
    Have to disagree with your application of the formula.

    A gun that's 95% reliable (i.e. misfires on one out of 20 shots, average) has a 46% chance of firing fifteen consecutive rounds without a malfunction. The 15/15 that you stated in the first equation is NOT "P(fire)" (a probability) - it is an outcome.

    You could, after your first 15 shots, conclude that the probability of a misfire is something less than 1/15 (0.0667), so the probability of the next 15 shots being successful is .9933^15 (= 35.5%) or better.

    If you've fired 100 consecutive good shots, then the probability of a misfire has been established at less than 1/100 (0.01). So, the probability of the next 15 shots being successful is 0.99^15 (= 86%) or better. The chance of the next 100 shots being flawless, on a purely statistical basis, can only be determined to be around 36% (0.99^100) or better. No matter how many times you fire a gun, you can never prove that it has a 100% chance of firing on the next shot, 'cause it just ain't so.

    Hope this helps.

    Regards,
    Jim
    Last edited by Kilowatt3; April 9th, 2011 at 12:56 PM. Reason: Left out a decimal point.

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    Really not a question that can be answered simply. There are too many variables involved. Caliber, material the gun is made out of, and the manufacturing tolerances used are all going to play into it.
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    Senior Member Array ICTsnub's Avatar
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    As I like to say, every break in shot puts you one closer to the first failure.

    For a group of people as safety obsessed as to fear an empty gun shooting us, it's a paradox how much we fear a loaded one going "click".
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    I am not a scientist nor do I play one on TV, but my answer is very simple. Everytime you pull the trigger there is a 50% chance it will work and another 50% it will not. It does not matter if it is a Glock, HiPoint, etc. I hope this helps. God Bless

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    Missed in all of the above to some extent, the science of statistics involves conducting an experiment, collecting results, collating and analyzing the results, and drawing inferences, usually in the form of probability, from the results of the experiment.

    What can be gleaned from an experiment depends on whether or not the experiment is adequate to the task of arriving at an answer.


    Firing 15 shots and collecting a single percentage of results really gets you nowhere. Similarly, firing a single series of 100 consecutive shots and trying to extrapolate to the future from what is really only one result, won't get you anything.

    Finally, nothing but experiments with lots of shots fired can incorporate the effects of wear, tear, accumulated dirt, on long term performance, which common sense tells us will degrade over time. In short, no matter what the results are with the first 100 to 1000 rounds, mechanical devices degrade with time and the results for the second 1000 rounds will possibly be a bit (or perhaps a great deal) worse.

    Ever notice how the auto- dealers like to tout the numbers for "initial reliability" or "initial customer satisfaction." These say nothing about what the car will be like after 3 years. Even a piece of junk might hold together for 10,000 miles.

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    A man boards a train carrying a gun going Eastbound.The train is doing 50 MPH................... ah forget
    RevolvingMag and TN_Mike like this.

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    Quote Originally Posted by HKinNY View Post
    A man boards a train carrying a gun going Eastbound.The train is doing 50 MPH................... ah forget
    Oh, you met my Algebra teacher.

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    Get a good quality revolver....No break-in period,,,,less to go wrong,,,,,,,and since they are not as much fun to shoot as a semi-auto, it will probably still be like new when you drop dead of old age.

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    Thing is, it isn't always "linear" like that. Some guns are super reliable up to a few hundred rounds, then have some part break that renders it inoperable. Your statistical projections would be useless in such an instance.

    It's also why it's always worth waiting, with new guns, for someone to test it out for several hundred to thousands of rounds to see if something breaks. It's easy to watch a video or text review where the author fired maybe 100-200 shots and had no failures, but it's going to suck when you buy it thinking it is reliable, only to have a trigger bar, recoil spring, or something else fail after 300 shots.

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    Quote Originally Posted by paul34 View Post
    Thing is, it isn't always "linear" like that. Some guns are super reliable up to a few hundred rounds, then have some part break that renders it inoperable. Your statistical projections would be useless in such an instance.

    It's also why it's always worth waiting, with new guns, for someone to test it out for several hundred to thousands of rounds to see if something breaks. It's easy to watch a video or text review where the author fired maybe 100-200 shots and had no failures, but it's going to suck when you buy it thinking it is reliable, only to have a trigger bar, recoil spring, or something else fail after 300 shots.
    This really raises an interesting question, I think. I've had one gun in which the recoil spring and guide rod failed dramatically after about 3 K rounds. I have another where I had to replace a manufacturer's original recoil spring with a Wolf spring, maybe with only about 1 K through it.

    These experiences have made me think twice and three times about doing a lot of shooting with an SD gun. It is sort of like keep two guns handy, just in case. Or, go the revolver route. (And neither gun was a "poor quality" el-cheapo.)

    My experience would lead me to advise keeping 2 handy or sticking with a revolver. I do neither though, and I can't say that I really am all that comfortable relying on my two auto loaders.

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    If a brand new semi-automatic handgun, properly cleaned and lubricated, using fresh quality ammunition, fired the first 15 shots without any malfunction, what is the statistical probability it will fire the next 15 shots without malfunction?
    If the gun in question is a "High Point", there is an excellent probability that something will break in the next 15 rounds.

    Does that probability increase significantly if it fires the first 100 shots without malfunction. If so, how much?
    Practical application and experience with various "High Point" pistols, would seem make that fact a near impossibility. While the math may seem to make it possible that it could in fact happen that the High Point could shoot 100 rounds without malfunction, it would be about as possible as walking both coasts and finding an ancient gold coin washed up on the beach. Sure it happens, but not often enough to be of any real concern.
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