Hey Airgunners read this very closely…
Your gun can vary in accuracy and it doesn’t mean your gun is broken or out of tune. You can limit bad accuracy by being fundamentally sound in your shooting but even with everything perfect you can still have really good results and some that aren’t so good. Practice good shooting and get good results.
Bryan Litz Ballistics
A dialogue on dispersion
A Beginner and a Guru meet on the range one day...
Beginner: "I just shot a 1/4 MOA 5-shot group!" (posts pic on facebook #AllDayLong)
Guru: "My guess; it's a 1/2 MOA rifle at best."
Beginner: "How do you figure?"
Guru: "Well, your excitement over this 1/4 MOA group means it's better than your average. A rare sample, probably a 1-in-20 group. Since dispersion is random, you'll shoot a wide range of group sizes. Some will be small (lucky) and others will be bigger (unlucky)."
Beginner: "I make my own luck. I mean, I just shot a 1/4 MOA group with this rifle and load, so that shows me the potential of how good it can be if I do my part."
Guru: "That's not how dispersion works."
Beginner: "What do you mean?"
Guru: "Well, if you shoot enough groups with enough different rifles/ammo, you'll see that the Standard Deviation (SD) in 5-shot group size is about 30% from 22 Rimfire up thru 375 cal. This means that even when everything about the rifle/ammo/shooter is the same, 2/3's of your groups will be +/- 30% from your average, and 19/20 of your groups will be +/- 60% from your average."
Beginner: "That sounds like BS."
Guru: "It's not. I'll show you. Let's assume that 1/4 MOA group you just fired is a 1-in-20 'good/lucky' group. That would put it 2 SD's from your average. If .25 MOA is two SD's from your average, and SD is 30% of the average, then I'm guessing your average group size is closer to 5/8 MOA ( .25 = (X - 2*.3*X) ... X = .25/.4 = .625 )."
Beginner: "Well, yea, I guess that is close to what the rifle groups on average. But I thought the bigger groups were due to something I'm doing wrong."
Guru: "It could be, and you should definitely keep paying attention to fundamentals and consistent shot execution. However, even if you were the perfect shooter, always shooting from a rock solid position, you would still see a wide range in group sizes. It goes the other way too. If your average group size is .625 MOA (5/8), then for every rare 'good' 1/4 MOA group you shoot, you're likely to also shoot a rare 'bad' group that would be 1 MOA."
Beginner: "How are you doing that math?"
Guru: "I'll take you thru it. 67% of your groups will be within +/- 1 SD from the average. So if your average is .625 MOA, then 2-out-of-3 of your groups will be between: .625 - .625*.3 = .438 MOA and .625 + .625*.3 = .813 MOA. Likewise, 95% of your groups will be within +/- 2 SD's from the average. This is from: .625 - 2*.625*.3 = .25 MOA to .625 + 2*.625*.3 = 1 MOA. In summary, for an average group size of .625 MOA (5/8 MOA), you will have:
2/3's of your groups between .438 MOA and .813 MOA, and
19/20 of your groups between .25 MOA and 1 MOA."
Beginner: "Damn, that is about what this rifle does in the long run, I just never thought of it like this."
Guru: "When you understand how dispersion really works, it changes your approach to a lot of things, especially load development and any area where you're trying to improve precision by small amounts like .6, .5, .4 MOA. When you realize that a precision rifle system can produce such a wide range of group sizes naturally, you will make better decisions about load development, handloading, etc. For example, if you shoot a 1 MOA group later today, you won't go home and cut your wrists, or change everything about your handloading because you shot a 'bad' group. Instead, you'll understand that .25 MOA and 1 MOA are both samples from the same population with an average of .625 MOA (5/8), and an SD of 30%."
Beginner: "That actually makes a lot of sense. So if my average group is 5/8 MOA, that means that 1/2 the groups I shoot will be bigger than 5/8's, and 1/2 will be smaller, right?"
Guru: "Approximately, yes."
Beginner: "Cool! Thanks man, I actually feel a lot better about this understanding than before when I thought I was just 'doing my part', not really knowing what part I was doing that mattered."
Guru: "HA! I know what you mean, we've all been there."
-end of dialogue-
Follow this page for more group discussions
www.thescienceofaccuracy.com
Your gun can vary in accuracy and it doesn’t mean your gun is broken or out of tune. You can limit bad accuracy by being fundamentally sound in your shooting but even with everything perfect you can still have really good results and some that aren’t so good. Practice good shooting and get good results.
Bryan Litz Ballistics
A dialogue on dispersion
A Beginner and a Guru meet on the range one day...
Beginner: "I just shot a 1/4 MOA 5-shot group!" (posts pic on facebook #AllDayLong)
Guru: "My guess; it's a 1/2 MOA rifle at best."
Beginner: "How do you figure?"
Guru: "Well, your excitement over this 1/4 MOA group means it's better than your average. A rare sample, probably a 1-in-20 group. Since dispersion is random, you'll shoot a wide range of group sizes. Some will be small (lucky) and others will be bigger (unlucky)."
Beginner: "I make my own luck. I mean, I just shot a 1/4 MOA group with this rifle and load, so that shows me the potential of how good it can be if I do my part."
Guru: "That's not how dispersion works."
Beginner: "What do you mean?"
Guru: "Well, if you shoot enough groups with enough different rifles/ammo, you'll see that the Standard Deviation (SD) in 5-shot group size is about 30% from 22 Rimfire up thru 375 cal. This means that even when everything about the rifle/ammo/shooter is the same, 2/3's of your groups will be +/- 30% from your average, and 19/20 of your groups will be +/- 60% from your average."
Beginner: "That sounds like BS."
Guru: "It's not. I'll show you. Let's assume that 1/4 MOA group you just fired is a 1-in-20 'good/lucky' group. That would put it 2 SD's from your average. If .25 MOA is two SD's from your average, and SD is 30% of the average, then I'm guessing your average group size is closer to 5/8 MOA ( .25 = (X - 2*.3*X) ... X = .25/.4 = .625 )."
Beginner: "Well, yea, I guess that is close to what the rifle groups on average. But I thought the bigger groups were due to something I'm doing wrong."
Guru: "It could be, and you should definitely keep paying attention to fundamentals and consistent shot execution. However, even if you were the perfect shooter, always shooting from a rock solid position, you would still see a wide range in group sizes. It goes the other way too. If your average group size is .625 MOA (5/8), then for every rare 'good' 1/4 MOA group you shoot, you're likely to also shoot a rare 'bad' group that would be 1 MOA."
Beginner: "How are you doing that math?"
Guru: "I'll take you thru it. 67% of your groups will be within +/- 1 SD from the average. So if your average is .625 MOA, then 2-out-of-3 of your groups will be between: .625 - .625*.3 = .438 MOA and .625 + .625*.3 = .813 MOA. Likewise, 95% of your groups will be within +/- 2 SD's from the average. This is from: .625 - 2*.625*.3 = .25 MOA to .625 + 2*.625*.3 = 1 MOA. In summary, for an average group size of .625 MOA (5/8 MOA), you will have:
2/3's of your groups between .438 MOA and .813 MOA, and
19/20 of your groups between .25 MOA and 1 MOA."
Beginner: "Damn, that is about what this rifle does in the long run, I just never thought of it like this."
Guru: "When you understand how dispersion really works, it changes your approach to a lot of things, especially load development and any area where you're trying to improve precision by small amounts like .6, .5, .4 MOA. When you realize that a precision rifle system can produce such a wide range of group sizes naturally, you will make better decisions about load development, handloading, etc. For example, if you shoot a 1 MOA group later today, you won't go home and cut your wrists, or change everything about your handloading because you shot a 'bad' group. Instead, you'll understand that .25 MOA and 1 MOA are both samples from the same population with an average of .625 MOA (5/8), and an SD of 30%."
Beginner: "That actually makes a lot of sense. So if my average group is 5/8 MOA, that means that 1/2 the groups I shoot will be bigger than 5/8's, and 1/2 will be smaller, right?"
Guru: "Approximately, yes."
Beginner: "Cool! Thanks man, I actually feel a lot better about this understanding than before when I thought I was just 'doing my part', not really knowing what part I was doing that mattered."
Guru: "HA! I know what you mean, we've all been there."
-end of dialogue-
Follow this page for more group discussions
www.thescienceofaccuracy.com
