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I have seen where some claim that accuracy as judged by a given MOA is less at say 100 yards than at a longer distance. Explanations have been to the effect that the bullet settles down or stabilizes. This makes no sense to me. I can easily understand that a bullet will slow down and become less stable and accurate with distance. I can see no logic to the statement that a bullet that may get 1 inch groups at 100 yards (1 MOA) would get 2 inch groups (1/2 MOA) at 400 yards. Physics would tell me that once a bullet started to stray off course it would continue its off course trajectory. Has any knowledgeable benchrest shooter actually seen the above phenomenen? | ||
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I have read of this happening with respect to 50 BMG target rifles but have never seen good evidence. Will be interesting thread. ________ Ray | |||
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l read a thread on this happeneing with the old Lee Enfields, and what was explained was this... When you look at a target at say 100yrds you may have a large xbull area to focus on (this may also be a problem if using high magnification scopes), but as you extend the range of the same target the bull becomes visually smaller and so your focus on the same target becomes more confined so removing the " where do l aim" issue... Just my 2penny worth. Dave. .... | |||
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Believe it - it's true for many bullets. Yesterday, for example, winds from 7-12 mhp cross range, I worked up 85 grain Sierra HPBT loads in my 6x45 fired from a 24" bbl AR15. At 100 yards groups averaged just over 1" (1.08" for 8 shots). At 300 yards groups averaged 1.9" (6 shot group). 60 grain Sierra Varminteer bullets averaged 0.85" at 100 yards (8 shot groups), and 1.8" (4 shot group) @ 300 yards. Yeh, I know more shots for the 60 & 85 @ 100 than at 300, but you get the idea. I've seen this same thing with my 6XC, .308, 300RUM, and 30-06. Mostly using match bullets. For example, looking back thru log book for 6XC. several groups 100 yards average 0.875", 300 yards average 2.125" - less than 3 times the 100 yard average (all 5 shot groups). Rem 260: 100 yards = 1.6", 300 yards 3.5" (no, this load didn't make the cut). 7mm Mag: 100 yards 1.05", 300 yards 2.375". ...and so on. I never count a load out just on 100 yard patterns - only if it bozo's at 300 or more. It doesn't happen all of the time, but does most of the time. Heavier bullets (and higher BC) appear to be more consistent in this behavior. It seems to me from experience that the 'average' average for group size reduction, when it happens, is to take the 100 yard load and plan on it being two-thirds/three quarters (??) the 'expected' size at 300 yards. Example: 100 yards 1", expect 3" at 300 yards, actually get 2+". Take a read from the Sierra manual - it gives all the warm and fuzzy math for this effect and cool words like nutation, precession, gyration, and such. Makes for good conversation when debating the preference for whale guns and torpedoes over a beer. Good luck 'Flinch | |||
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This has been discussed on this forum in the past. You might check the archives. You can get freak groups at any yardage at times. A consistant 1"MOA rifle will not shoot smaller at longer yardages. Once a bullet is on its path, what will alter their path to converge? How will each of the bullets in say a 5 shot group know where to go. Butch | |||
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Once a bullet's left the barrel, it can only change its trajectory by external forces acting on it. No way can a bullet at some mid range point know what direction to go so accuracy further down range will be better; if it did, it would have to know where in the mid range group it was at so it would know which way to move. All sorts of "reasons" why have surfaced over the years but none hold water. Bullets that aren't spun fast enough when fired may nutate more at longer ranges as they are gyroscopically more unbalanced which causes them to have more drag so they slow down faster. And sometimes when this happens, they change direction a bit which degrades accuracy. This often happened with the US military M852 7.62mm NATO match ammo loaded with Sierra 168-gr. HPMK bullets fired from 22-inch M14/M1A 1:12 twist barrels that weren't tight enough to spit 'em out over 2600 fps. 1:11 twist 22-inch barrels spun the 168's fast enough that this problem didn't happen. Vertical shot stringing resulting in smaller groups at longer ranges does happen with some rifles. The British SMLE rear-locking bolt action rifle is well known amongst long range highpower competitors as notorious for this. Especialy when ammo loaded with Cordite was used as its muzzle velocity spread was quite a bit. All rifle barrels go through less than one major vibration cycle when fired; their resonant frequency is usually 40 - 60 Hz. The SMLE's whip due to action design is much more than front-locking Mauser style actions. The Brits proved years ago that bullets loaded with Cordite leaving SMLE's at the low end of the muzzle velocity spread left the barrel later in its upward swing so the departure angle is higher than bullets leaving at the higher end of the muzzle velocity spread. Which meant at ranges greater than 600 yards, their accuracy actually improved as bullets that would normally drop more from lower muzzle velocity would be fired at a slightly higher elevation angle and the opposite would happen with higher muzzle velocities. This is known as positive compensation. When modern extruded or ball powders producing smaller muzzle velocity spread are used in SMLE's, this phenomenon is reduced, but still there. US military tests with M14NM rifles proved that a small amount of positive compensation at long range happened with M118 and M852 match ammo. They attributed this to the barrel's gas port being about mid point in the barrel length which bowed the barrel up a bit causing the muzzle axis to point lower just a little when higher pressures happened so the faster bullet would leave at a slightly lower elevation angle. M1 30 caliber rifles with their gas port close to the muzzle never exhibited this phenomenon. Bart B. | |||
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I won't look up the proper terminology but yes it can occur especially in cartridges like 6.5x55 or 7x57 with the heaviest bullets.The reason is that the bullets wobble as they come out of the barrel therefore adding inaccuracy to them. As the bullet travels further the wobbling decreases removing that inaccuracy factor !!So you might get 1" group at 100 yds and 1.5" at 200 yds !!! It's a fact !...Google "bullet wobble" and you'll get sites that explain wobble , precessing etc. | |||
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Butch, I been out of BR awhile, but aren't good groups at 100yds about 2/3rds the size at 200 under similar circumstances? Rich DRSS | |||
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Rich, it may be a little closer. You can shoot groups with a smaller MOA at a longer range a few times, but it didn't start out larger and converge smaller at a longer range. I don't care about wobble or anything else it just don't happen. As stated above, when a group of bullets go off in their own direction, how do they know how to get back in a group. If they did, do they then stay together or do they go off in another direction? Butch | |||
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Interesting theory on all those web sites. But nobody has ever explained how bullets at the lower left hand part of the short range group change their trajetory up and to the right as well as all the other bullets at other places near the edge of the short range group change direction towards the long range center. In order to have smaller subtended group angles at longer ranges than shorter ranges, bullets have to change direction towards group center. I don't know of anybody who has shot through several electronic targets placed and fixed range intervals to show exactly where the bullet is relative to group center at different ranges. This is about the only way one can prove that bullets near the edge of one ranges group change direction such that down range groups are smaller. Vertical shot stringing caused by positive or negative compensation excepted. Bart B. | |||
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In a vacuum NO. But after only seven years of 1000 yard bench rest shooting I have seen stranger things happen. Blame it on the wind. But a gun that shoots 1/3 moa consistantly will in the long run agg. better than one that shoots 1/5 moa consistantly. | |||
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I meant to say 1/2 moa. | |||
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1/2 MOA for which, the 1/3rd or 1/5th? I hope you are saying the 1/3Moa will agg better than 1/2MOA. Butch | |||
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Something is inconstant here. I don't know of any gun that shoots any size groups consistantly. They all vary by some amount. And the fewer shots per group the more they'll vary. Well, maybe if you shot several groups with a few hundred shots per group, their sizes would have a variance of well under 5 percent. Bart B. | |||
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Something is inconstant here. I don't know of any gun that shoots any size groups consistantly.[/QUOTE] Bart If you are going to compete at Benchrest you damn well better have a rifle that shoots consistently. Otherwise you won't be hearing your name called during the awards ceremony. The difference between the winners and the losers is the shooter. Ray Arizona Mountains | |||
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Easy test: line up paper targets at several ranges (100, 200, 300 yards/meters) so you shoot thru them simultaneously and note the results. Bob Shaffer | |||
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Is it possible that bullet paths diverge when leaving the barrel then become more in parallel as the spin stabilizes? | |||
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Anybody tried it? Bob Shaffer | |||
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An interesting dialog, but some of this approaches the Kennedy/Connely bullets. There was a grassy knoll, wasn't there? | |||
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I think it possible that the bullet could stabilize after a bit of flight. This would keep divergence from being as severe but I can't see how it would make the bullets turn to a more parallel course. In other words, if the gun shot 1 MOA at 100 yards, it should never shoot better than 1 MOA at 200 yards. | |||
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I'm not a long range shooter, and I've never posted on this part of AR, but reading you guys got me to wondering. What if the bullet's flight is not a straight line with only air and gravity working on it? What if in fact the bullet is on a tight spiral? As it goes downrange and the bullet "stabilizes" that spiral would tend to diminish. This could explain why it achieves a better MOA at a longer range. I was just thinking about footballs in flight and this occured to me. _________________________________ AR, where the hopeless, hysterical hypochondriacs of history become the nattering nabobs of negativisim. | |||
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Among a few others--Mausers--I have an unissued 1909. For better or worse, a previous owner mounted a Lyman 57 on this otherwise pristine collector's item. With a front globe sight. I've worked up loads on the 100 yd range. And knew it shot well. But on the 200 yd. range, a few weeks back, it shot a 1.65" group. I don't believe it was a ballistics issue. For some reason, I had intuited that this rifle would do well at 200 yds. Long sight radius, the inherent accuracy of the aperture/front globe setup? Most, I guess, believe that iron sights take second place to scopes. Under certain circumstances, I'm not certain this is true. Comments? flaco | |||
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It is my understanding that some bullets in some barrels not only spin when they exit but spiral on one or even several different axis. Under the right conditions I believe diminishing MOA could happen, however I am not one with enough knowledge in this area to explain exactly how this would be possible. | |||
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Uhhh...HELLO...KNOCK KNOCK KNOCK TWICE I HAVE POSTED A SIMPLE TEST FOR THIS OF SHOOTING THROUGH PAPER TARGETS AT VARIOUS RANGES, YET NOBODY SAYS THEY HAVE OR WILL TRY IT. YOU GUYS WANT TO FIND SOMETHING OUT OR JUST ENJOY YAKKING? Bob Shaffer | |||
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sonofagun You're wasting your time trying to reason with these guys. As you and I and Butch Lambert, and many others have tried to point out, proof on paper is all we ask and we will become believers. But the subject comes up at least 2 or 3 times a year, always with the same kind of comments and the same result. For me, it's not worth my time anymore. Ray Arizona Mountains | |||
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I hear ya. If anything, the opposite is more likely - increased MOA grouping as the range increases due to various factors, mostly wind. Anything else can only be a fluke. Those who want to prove anything else, do my paper target test and post the results here; five shot groups at least; 10 is better. Bob Shaffer | |||
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I'm new here and would like to get my feet dirty on this one. A bullet does not fly in a perfectly straight line to the target but rather corkscrews though the air resulting in some of the observations discussed earlier. There is a point in the bullets flight where the optimum stability is reached and it probably is not at exactly 100 yards where much load testing is done. The bullets rate of spin, velocity, SD, weight, length, etc. all play a part and optimal stability happens when all these factors come together at some point downrange which would explain differing MOA’s at various ranges. This concept is not new by any means as I learned it years ago in practical rifle 101. testing is done. | |||
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OK vin, let's see the results of the tests. That's all that any of us have asked for. Ray Arizona Mountains | |||
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Cheechako; That last line about testing was a miss print. I did not intend for that line to be inserted by my copy/paste from my word processor editor. It was left over from earlier in the post where I said most "testing is done" at 100 yds. I didn't see a way to edit the post after I posted it. Sorry. I'm not sure how to go about testing. I do think the concept is sound JMHO | |||
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Not sure how testing is done? OK, I'll 'splain it so EVERYONE here can understand: You line up paper (lightweight such as standard 20#) exactly in line at several distances (such as 50, 100, 200, 300, etc. yards) with no backstop except the last target. Align targets so the bullets will pass thru all the targets. Fire some groups this way and you can then see where the bullet(s) were at each yardage. Fire at least five 5 shot (or more) groups and then post the pictures here. Got it? Corkscrews thru the air? No, it travels in a ballistic arc subject to lateral wind drift. In a vacuum away from a gravitational field it would travel in an optically straight line (constant vector). Bob Shaffer | |||
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Thanks, sonofagun for your thoughtful explanation. I do have another question that maybe you could answer …. Since we do live on earth and our bullets are affected by gravity and varying atmospheric conditions and we put rifling in our barrels to overcome these obstacles then why do we have to have so many twist rates in our barrels? What happens to these bullets fired in a barrel without an optimum twist rate and how do they fly through the air into poor groups on paper? | |||
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An insufficient twist rate will cause a bullet to wobble in flight (sometimes even keyholing) leading to poor accuracy. I was speaking of bullets spinning at optimal rates for stable flight characteristics. Think I'll sign off on this until somebody posts some targets. Bob Shaffer | |||
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Since I live at the rifle range I would be happy to do this experiment but to cover even 300 yards my first target would have to be 20' off the ground since my range is uphill. This would be a little hard to set up. | |||
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I'll leave this post also as everybody that says that it can happen doesn't support it with evidence or has an excuse for not doing sonofaguns test. Butch | |||
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Does anyone have any idea if shooting through 4 or 5 pieces of paper at the same time would have any effect on the bullets flight. That is one experiment I could set up and it would seem to be a rational place to start before trying to line up targets over extended range. Just this weekend I shot groups at 100 yds that measured around 1 moa and then at 300 yds that were .45 moa. I did this twice in a row. I know that this doesn’t prove anything but I have had this experience quite often in the past. One set was fired in calm conditions and the (smallest) group was fired in driving rain with about a 15 mph full value wind. I have an indoor shooting position right next to my loading bench. .308, 175 SMK, 2650 fps | |||
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Well....why don't you post YOUR TARGETS then and quit your griping? It's your idea so feel free to go ahead and educate the rest of us, instead of expecting someone else to do it for you. I doubt if anything would be proven anyway, since you would have to use multiple loads with a variety different bullet designs and multiple rifles. Should take quite a while and considerable expense - unless you can find someone with a proven rifle and load that is shooting decreasing MOA and would lend it to a person as grouchy as yourself. | |||
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toad What you're asking sonofagun to do is to prove a negative. Like myself and Butch he says that it can't be done. There are guys on this very thread who say it can and we are simply asking them to show us. If you visit this Forum often you will see that this subject comes up a couple of times a year with different shooters saying that they have rifles that will show decreasing MOA accuarcy as the distance is increased. Every time these threads start we simply ask them to show us on paper. To date, no one has done it. That's all we're asking, again. I don't see where it would be a lengthy or expensive test. If you have a load that you are convinced will do it, them simply set up the targets and show us how. I have tried it myself and it didn't work. And I have never seen anyone do it. Sure we have all shot individual groups at 200 and 300 yards that are smaller than groups that we shot at 100. Even on the same day. But you guys are saying that certain rifles or loads will do this consistently with one load. And there's no reason to get personal and nasty about it. Ray Arizona Mountains | |||
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So even if I built the damn 20’ vertical extension for my 100 yard target to line it up with my 300 yard target, how many groups would it take to “prove†this. I would bet about a thousand because the results would be endlessly picked apart but I’ll try and take some of my jerkin’ off in the forum time and actually do it…. Anything to keep my round count up and my forum post count down. | |||
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In case anyone is interested here are 2 website addresses that provide some info on how a decreasing MOA might be possible. www.the-long-family.com/bullet_dispersions.htm and www.nennstiel-ruprecht.de/bullfly/index.htm | |||
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The Accurate Reloading Forums THE ACCURATE RELOADING.COM FORUMS Shooting Benchrest & Target Shooting Decreasing MOA with distance; does it really happen?
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