timlt
11-15-2006, 04:20
You've heard of bipolar disorder: victims suffer from swings between two polar opposite and unhealthy emotional states, mania and depression.
Apparently some Mini's also have a type of bipolar disorder in the area of accuracy. To be more precise, some of us have noticed that even with an accurized Mini, you can swing wildly and unpredictably between two opposite extremes of accuracy on the one hand, and massive inaccuracy or "frequent flyers" on the other hand, so that your resulting target shows a "bimodal pattern" of grouping.
This is paradoxical. On the one hand, you can sometimes shoot highly accurate, sub MOA groups from an accurized Mini that will rival a bolt gun. But on the other hand, within the same shooting session and often within the same string of shots, you will also get groups that are wildly inconsistent and where the point-of-impact (POI) is WAY off--from 3 to 15 inches or more--from your zeroed sights and established point-of-aim (POA). The end result is, you'll often see two clusters of shots on your target: one being roughly where the POI EQUALS the POA (when the shots fall where you aimed them), the other being a looser but still noticeable grouping of the flyers that occurs when the shots go repeatedly astray from your point of aim. Sometimes you can shoot small clusters of three or four shots in a good group, and then you get a flyer. Other times, you may find it alternating every other shot, with first a good shot, then a flyer, then a good shot, etc.
I have noticed this pattern in my own Mini. In another thread, where I traced the process of gradually trying to improved the accuracy of my new Mini (http://www.perfectunion.com/vb/showthread.php?t=53855 ), I noted this pattern. After Gundoc did his excellent work to accurize my Mini, as I noted in the thread, the rifle was shooting better than ever. Since the mods, I have been able to shoot in every range session several groups of 3 to 4 consecutive shots that average just over an inch. That was the good news. But the bad news, which I also noted in that thread, was that I was still having this "bimodal pattern" when I factored in larger groups.
A number of other folks on this forum, including Kkina, have told me that they too experience this bimodal pattern of grouping, even with accurized Minis that they are otherwise happy with and consider to be excellent rifles. And I would expect that some form of this problem, in varying degrees, afflicts a very large number of Mini's out there. While all the mods that we commonly do on our rifles are useful and necessary, there must still be some common issue in the rifles that is not widely known about yet, and that is causing the behavior. Some speculate that there may be some movement in the gas block causing the bimodal pattern, and have experimented with bedding the gas block, but from a quick search and review of threads on this subject, I have not seen any comprehensive solutions that have diagnosed the common problem and found a definite cure yet.
I'm curious to learn the following:
* How many folks experience some form of this bimodal grouping pattern in your shooting results? What are the "magic" numbers of rounds in your groups when you begin to see the flyers and the pattern emerging?
* If your gun is accurized, what mods have you done? Have you tried anything else on your gun to address the bimodal grouping?
* Any ideas on possible tests that could be used to firmly establish the CAUSE of this problem? Any ideas on possible solutions to the problem, aside from the normal accurization mods which many of us do (The normal mods are still helpful and necessary, but don't seem to address this problem)?
As a follow-up point, to give some starter data for discussion, I shot some targets at the range today to illustrate the issue. All shots were fired from my accurized Mini, 100 yards with a red dot scope, or from my factory non-modded Browning A-bolt (.223), using a Bushnell scope at 9x. I shot Federal American Eagle 50gr HP in both. Let me explain what each of the four targets illustrate (each target picture has a text label added to the picture that I'll use to refer to them below):
Mini-14 (1): This one shows my first 10-shot group, fired from a cold Mini. Surprisingly, in today's session my first shot was NOT a ridiculously wild flyer, which it usually is in 80% of range sessions. You can quickly see the bimodal pattern forming, with the shots including the bullseye and the shots in the black to the right of it forming a 5-shot cluster (this was NOT a consecutive group, though), and then the 4 flyers wide right are circled. The inconsistency was bad on this group: it would alternate back and forth EVERY shot, from flyer, to good shot, to flyer.
A-bolt (1): This one shows a 10-shot group fired from the cold A-bolt. This gun, true to form, was dead-on. The entire 10-shot group size is just under 2.25". And this is slightly worse than normal for this rifle. My first 8 shots are actually a group in this picture, and if you measure just them (excluding the circled ones), the group size is 1.75" with 5 bullseyes. Then I think because I was shooting too quickly, I shanked the last two shots (the circled ones) and that's what opened the total group up to 2.25". Still, this is a decent group for the purpose at hand. The most important point for this discussion is, this rifle doesn't show the same bimodal pattern of the Mini, with the same shooter, and the same ammo and the same shooting conditions, so that's some evidence that the problem must be in the Mini rifle.
Mini-14 (2): This was a second group from the Mini, only a 5-shot group this time. I stopped after 5 because it nicely illustrates how the bimodal pattern form in 5 shots (this is amazingly consistent in my rifle, it almost ALWAYS happens!). Note that the Mini had been sitting there for a while as I shot the Browning, and it was quite cold, so the rifle had cooled off. And as you might expect, my first 2 shots were the 2 flyers you see outside the black, to the right. This is what I typically get on my first shots from a cold barrel. The next 3 consecutive shots formed a group around the bullseye.
Mini-14 (3): This was my last and best string from the Mini for the day. It was a 10-shot group, and here you see only one flyer wide right, with the rest in the black. In the middle of the string, I had 4 consecutive shots (circled) that formed a group. But again, as some have pointed out (and I wholeheartedly agree), such groups as this 4-shot group are probably not as good news as I would like, because I cannot CONSISTENTLY shoot that group ANYTIME I WANT. I can only repro good groups like that SPORADICALLY, by firing larger groups of say 10 shots or more and choosing the best consecutive string of 3 or 4 shots. And the overall group size here of the 10-shot group is not good considering how the rifle can shoot 3- and 4-shot groups: it's 5.15". Pretty clearly, the RIFLE IS THE LIMITING FACTOR here, because of the flyers. The rifle is unpredictably shifting the POI to the right of my POA as frequently as every other shot, or as rarely as once or twice in 10 shots (as you see in this target), but regardless, it happens at least once in every 10 shots I fire.
Putting all this in perspective, my mini's group size today, with 10-shot groups of 8" and 5.15", and a 5-shot group of 5.25", averaged 6.13". Though I didn't have time to shoot more groups with the A-bolt, I can tell you that based on past performance, the 2.25" group I shot today was a little below average, but close enough to establish the general point that the Mini has this bimodal grouping pattern, and that more generally, the Mini is quite inconsistent overall and unable to keep 10 or even 5-shot groups in a reasonably tight pattern.
Now someone may object: Yes, but you were using a 9x scope on the A-bolt and no magnification on the Mini. And the A-bolt is an inherently accurate bolt gun, whereas the Mini is a semi-auto. Both points are true, but my expectation here is NOT that the Mini should shoot exactly like the Browning. I was not using the Browning for direct comparison, I was using it as a "control group" in my testing to illustrate that the bimodal grouping problem is confined to the Mini. By shooting a much tighter group with the Browning and using the same ammo, it helps me to rule out that the shooter and the ammo as likely causes of the Mini's problems.
Now, though I don't expect the Mini to shoot exactly as well as an A-bolt, my ACCURIZED Mini has been shooting 3- and 4-shot consecutive strings that group into an inch, and a few times even sub MOA. The Mini is not an A-bolt, but given what it can do when it's not throwing flyers, I would expect it to do a LOT better than 6" avg. group size. Even if I did use the same scope that's on the Browning, that would only help me to group my shots that were ALREADY IN THE BLACK a little tighter. The scope wouldn't prevent the flyers from happening, and they are what caused the 6" groups, not the distance between the shots in the black. So yes, I do expect the Mini should be able to group in 3", at 100 yards.
And now the larger concern comes into play. It's not JUST about group size here. Group size in this case indicates the rifle's potential for accuracy, and if a rifle is truly as inconsistent as these groups indicate, it's hard to imagine any scenario in which you'd use the rifle that you'd really find such inconsistency (and the resulting inaccuracy in a too-high percentage of your shots) to be acceptable. Whether shooting local competition matches, hunting, or defending yourself, flyers that can go anywhere from 3" to 15" (that's the usual range of my flyers) with a frequency of at least once, and often 2 to 4 times, every 10 shots, have a tendency to cause you to doubt whether you can rely on your rifle when you need it.
Anyway, sorry this got long, but I'm really hoping we can pool the ingenuity of folks on this forum and find some kind of solution that will help everybody who experiences this issue. I think this problem causes a really fun, reliable, great rifle to be less than it can be. [Edited for typos and clarification].
Apparently some Mini's also have a type of bipolar disorder in the area of accuracy. To be more precise, some of us have noticed that even with an accurized Mini, you can swing wildly and unpredictably between two opposite extremes of accuracy on the one hand, and massive inaccuracy or "frequent flyers" on the other hand, so that your resulting target shows a "bimodal pattern" of grouping.
This is paradoxical. On the one hand, you can sometimes shoot highly accurate, sub MOA groups from an accurized Mini that will rival a bolt gun. But on the other hand, within the same shooting session and often within the same string of shots, you will also get groups that are wildly inconsistent and where the point-of-impact (POI) is WAY off--from 3 to 15 inches or more--from your zeroed sights and established point-of-aim (POA). The end result is, you'll often see two clusters of shots on your target: one being roughly where the POI EQUALS the POA (when the shots fall where you aimed them), the other being a looser but still noticeable grouping of the flyers that occurs when the shots go repeatedly astray from your point of aim. Sometimes you can shoot small clusters of three or four shots in a good group, and then you get a flyer. Other times, you may find it alternating every other shot, with first a good shot, then a flyer, then a good shot, etc.
I have noticed this pattern in my own Mini. In another thread, where I traced the process of gradually trying to improved the accuracy of my new Mini (http://www.perfectunion.com/vb/showthread.php?t=53855 ), I noted this pattern. After Gundoc did his excellent work to accurize my Mini, as I noted in the thread, the rifle was shooting better than ever. Since the mods, I have been able to shoot in every range session several groups of 3 to 4 consecutive shots that average just over an inch. That was the good news. But the bad news, which I also noted in that thread, was that I was still having this "bimodal pattern" when I factored in larger groups.
A number of other folks on this forum, including Kkina, have told me that they too experience this bimodal pattern of grouping, even with accurized Minis that they are otherwise happy with and consider to be excellent rifles. And I would expect that some form of this problem, in varying degrees, afflicts a very large number of Mini's out there. While all the mods that we commonly do on our rifles are useful and necessary, there must still be some common issue in the rifles that is not widely known about yet, and that is causing the behavior. Some speculate that there may be some movement in the gas block causing the bimodal pattern, and have experimented with bedding the gas block, but from a quick search and review of threads on this subject, I have not seen any comprehensive solutions that have diagnosed the common problem and found a definite cure yet.
I'm curious to learn the following:
* How many folks experience some form of this bimodal grouping pattern in your shooting results? What are the "magic" numbers of rounds in your groups when you begin to see the flyers and the pattern emerging?
* If your gun is accurized, what mods have you done? Have you tried anything else on your gun to address the bimodal grouping?
* Any ideas on possible tests that could be used to firmly establish the CAUSE of this problem? Any ideas on possible solutions to the problem, aside from the normal accurization mods which many of us do (The normal mods are still helpful and necessary, but don't seem to address this problem)?
As a follow-up point, to give some starter data for discussion, I shot some targets at the range today to illustrate the issue. All shots were fired from my accurized Mini, 100 yards with a red dot scope, or from my factory non-modded Browning A-bolt (.223), using a Bushnell scope at 9x. I shot Federal American Eagle 50gr HP in both. Let me explain what each of the four targets illustrate (each target picture has a text label added to the picture that I'll use to refer to them below):
Mini-14 (1): This one shows my first 10-shot group, fired from a cold Mini. Surprisingly, in today's session my first shot was NOT a ridiculously wild flyer, which it usually is in 80% of range sessions. You can quickly see the bimodal pattern forming, with the shots including the bullseye and the shots in the black to the right of it forming a 5-shot cluster (this was NOT a consecutive group, though), and then the 4 flyers wide right are circled. The inconsistency was bad on this group: it would alternate back and forth EVERY shot, from flyer, to good shot, to flyer.
A-bolt (1): This one shows a 10-shot group fired from the cold A-bolt. This gun, true to form, was dead-on. The entire 10-shot group size is just under 2.25". And this is slightly worse than normal for this rifle. My first 8 shots are actually a group in this picture, and if you measure just them (excluding the circled ones), the group size is 1.75" with 5 bullseyes. Then I think because I was shooting too quickly, I shanked the last two shots (the circled ones) and that's what opened the total group up to 2.25". Still, this is a decent group for the purpose at hand. The most important point for this discussion is, this rifle doesn't show the same bimodal pattern of the Mini, with the same shooter, and the same ammo and the same shooting conditions, so that's some evidence that the problem must be in the Mini rifle.
Mini-14 (2): This was a second group from the Mini, only a 5-shot group this time. I stopped after 5 because it nicely illustrates how the bimodal pattern form in 5 shots (this is amazingly consistent in my rifle, it almost ALWAYS happens!). Note that the Mini had been sitting there for a while as I shot the Browning, and it was quite cold, so the rifle had cooled off. And as you might expect, my first 2 shots were the 2 flyers you see outside the black, to the right. This is what I typically get on my first shots from a cold barrel. The next 3 consecutive shots formed a group around the bullseye.
Mini-14 (3): This was my last and best string from the Mini for the day. It was a 10-shot group, and here you see only one flyer wide right, with the rest in the black. In the middle of the string, I had 4 consecutive shots (circled) that formed a group. But again, as some have pointed out (and I wholeheartedly agree), such groups as this 4-shot group are probably not as good news as I would like, because I cannot CONSISTENTLY shoot that group ANYTIME I WANT. I can only repro good groups like that SPORADICALLY, by firing larger groups of say 10 shots or more and choosing the best consecutive string of 3 or 4 shots. And the overall group size here of the 10-shot group is not good considering how the rifle can shoot 3- and 4-shot groups: it's 5.15". Pretty clearly, the RIFLE IS THE LIMITING FACTOR here, because of the flyers. The rifle is unpredictably shifting the POI to the right of my POA as frequently as every other shot, or as rarely as once or twice in 10 shots (as you see in this target), but regardless, it happens at least once in every 10 shots I fire.
Putting all this in perspective, my mini's group size today, with 10-shot groups of 8" and 5.15", and a 5-shot group of 5.25", averaged 6.13". Though I didn't have time to shoot more groups with the A-bolt, I can tell you that based on past performance, the 2.25" group I shot today was a little below average, but close enough to establish the general point that the Mini has this bimodal grouping pattern, and that more generally, the Mini is quite inconsistent overall and unable to keep 10 or even 5-shot groups in a reasonably tight pattern.
Now someone may object: Yes, but you were using a 9x scope on the A-bolt and no magnification on the Mini. And the A-bolt is an inherently accurate bolt gun, whereas the Mini is a semi-auto. Both points are true, but my expectation here is NOT that the Mini should shoot exactly like the Browning. I was not using the Browning for direct comparison, I was using it as a "control group" in my testing to illustrate that the bimodal grouping problem is confined to the Mini. By shooting a much tighter group with the Browning and using the same ammo, it helps me to rule out that the shooter and the ammo as likely causes of the Mini's problems.
Now, though I don't expect the Mini to shoot exactly as well as an A-bolt, my ACCURIZED Mini has been shooting 3- and 4-shot consecutive strings that group into an inch, and a few times even sub MOA. The Mini is not an A-bolt, but given what it can do when it's not throwing flyers, I would expect it to do a LOT better than 6" avg. group size. Even if I did use the same scope that's on the Browning, that would only help me to group my shots that were ALREADY IN THE BLACK a little tighter. The scope wouldn't prevent the flyers from happening, and they are what caused the 6" groups, not the distance between the shots in the black. So yes, I do expect the Mini should be able to group in 3", at 100 yards.
And now the larger concern comes into play. It's not JUST about group size here. Group size in this case indicates the rifle's potential for accuracy, and if a rifle is truly as inconsistent as these groups indicate, it's hard to imagine any scenario in which you'd use the rifle that you'd really find such inconsistency (and the resulting inaccuracy in a too-high percentage of your shots) to be acceptable. Whether shooting local competition matches, hunting, or defending yourself, flyers that can go anywhere from 3" to 15" (that's the usual range of my flyers) with a frequency of at least once, and often 2 to 4 times, every 10 shots, have a tendency to cause you to doubt whether you can rely on your rifle when you need it.
Anyway, sorry this got long, but I'm really hoping we can pool the ingenuity of folks on this forum and find some kind of solution that will help everybody who experiences this issue. I think this problem causes a really fun, reliable, great rifle to be less than it can be. [Edited for typos and clarification].