GROUP SIZE, 100/200 YARDS

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  • Last Post 28 January 2020
joeb33050 posted this 26 January 2020

From 1999 to 2019, CBA NM data shows

5 shot 200 yard groups were 2.251 times as large as 5 shot 100 yard groups,

10 shot 200 yard groups were 2.35 times as large as 10 shot 100 yard groups.

The reason that the ratios are greater than 2 is that the bullets are accelerated away from the center; else the ratio would be 2.

The Houston Warehouse report states that indoors, the ratio = 2.

This suggests that cast bullet shape and SD, the Ballistic Coefficient, is one of the primary causes of inaccuracy.

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beltfed posted this 26 January 2020

--Time of Flight in the "second" hundred yards is greater and therefore

prevailing conditions. wind, have greater effect

---Destabilization effects, especially if twist is borderline sufficient as bullet slows down.

beltfed/arnie

 

 

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beltfed posted this 26 January 2020

As bullet velocity drops in second hundred yards, it also may hit transonic turbulence

depending on how fast it started out, of course.

beltfed/arnie

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joeb33050 posted this 26 January 2020

--Time of Flight in the "second" hundred yards is greater and therefore

prevailing conditions. wind, have greater effect

---Destabilization effects, especially if twist is borderline sufficient as bullet slows down.

beltfed/arnie

Wind effect varies as velocity-actually speed, is reduced over the range.  Thus wind effect is LESS from 100-200 than from 0-100.

 

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joeb33050 posted this 26 January 2020

As bullet velocity drops in second hundred yards, it also may hit transonic turbulence

depending on how fast it started out, of course.

beltfed/arnie

Trans sonic turbulence affect on accuracy is a myth.

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joeb33050 posted this 27 January 2020

https://rugerforum.net/reloading/133750-transonic-accuracy.html

 

rorshach1980, Sonic transition is the biggest farce since the tooth fairy. Some people think when a bullet transitions from supersonic to sub sonic (about 1100 fps) all of a sudden the bullet goes crazy and accuracy goes down the tubes. Fact is, sonic transition in it's worst case scenario is nothing more than a slight "bump in the road" that has virtually no affect on accuracy.

Light small diameter bullets are affected more by sonic transition than heavier and larger diameter bullets, because heavier bullets have better gyro stability. Worst case would be a light 22 LR with a very poor ballistic coefficient (BC). A 40gr HV 22 LR leaves the muzzle at about 1250 fps and at about 30~35 yards, it slows down to 1100 fps and transitions to subsonic. I think we all know ... a 22 LR can be very accurate out to 100 yards or more ... 65~70 yards AFTER it went through sonic transition.

Handgun bullets typically have a poor BC, meaning air friction slows them down pretty fast. One of the worst case examples is a factory load 115gr 9mm FMJ bullet that leaves the muzzle at 1155 fps and goes sub sonic before it reaches 20 yards. Again, I think we all know a light 115gr 9mm bullet will maintain stability out to 100 yards or more. BTW, 9mm pistols have about the fastest twist rate of any handgun .... 1:10, whereas a 38 Special/357 Mag has a slow TW of 1:18.75

How can you tell when a bullet becomes unstable? If you examine your paper target and experiment at different distances, you will see holes get oval shaped as bullets start to yaw. Soon after, bullets will begin to tumble and will create "keyholes" in the paper target. The distance where you first see oval holes is called the point of instability.

This sonic transition "theory" started back in the 1960's when the military went to M-16 rifles that initially had a twist rate of 1:12 and fired a 55gr FMJ with a very poor BC of .103. Turns out, bullets would become unstable and start to tumble at about 250 yards and by 300 yards, every bullet was printing keyholes in the paper target. By coincidence, bullets went through sonic transition at about 250 yards so someone came up with the wild idea that it was sonic transition that caused bullets to become unstable. Of course this story spread like wildfire and here we are 50 years later where the fairy tale is still believed to be gospel. Funny thing .... when the military later changed the twist rate in M-16s to 1:10, the same exact 55gr FMJ ammo would maintain stability to about 400 yards, yet when it was chronographed at 250 yards, it was still 1100 fps ... the same as when the twist rate was 1:12. Of course the general public never connected the dots. What does this tell you? It tells me the sonic transition theory is a bunch of crap.

In more recent years, high speed video photography has been able to capture pictures of bullets going through sonic transition. In these pictures, lighter bullets experience a slight "bump" then recover back to their normal flight path. With heavier and larger diameter bullets, there is no visible "bump" at sonic transition.

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joeb33050 posted this 27 January 2020

hmendelson1946, Your explanations is exactly what I was trying to debunk. I don't doubt all that rhetoric happens ... and let's assume it does. The bottom line is ... did it affect the accuracy of the bullet within its usable range? Better yet, if it did affect the bullet's accuracy, how far downrange did this happen?

One of the classic experiments involves a 223 Rem cartridge, 55gr FMJ .224 bullets because they have a grim BC ... less than .200 in the book, about .150 in actual tests. The muzzle velocity is 3240 fps from a bolt action 24" barrel, 1:12 TR. These bullets go subsonic at about 300 yards and by 350 yards, the bullets are flipping end over end. This would make a person think it was sonic transition that caused this event. Take the same exact ammo and fire it from a faster twist barrel ... ie a AR-15 with a 1:9 TR 20" barrel at 3100 fps. Turns out this bullet will go subsonic at about 260 yards ... 40 yards sooner because MV was lower. Strange thing is ... the bullet now maintains stability and good accuracy to more than 400 yards. If sonic transition is so dramatic, why does this little bullet stay stable more than 150 yards after passing through sonic transition???

Let's apply some more practical applications. Typical bullets used for hunting big game have lower BCs than bullets used for long range target shooting. A typical hunting bullet from most any high power rifle will maintain stability well past it's effective hunting range. Using a 30-'06 as an example with a 180gr bullet (BC=.350) fired at 2700 fps, it will go subsonic at 450 yards. So assuming the bullet goes totally crazy when it passes through sonic transition, the effective stability range still exceeds the effective hunting distance by about 200 yards.

Lets take another 30'06 cartridge only this time let's use a 168gr match bullet with a BC of .600. It will travel 730 yards before it goes through sonic transition. In a 300 Win Mag rifle, the same bullet can go in excess of 1000 yards before it transitions to subsonic. Guys, that's a LONG ways and so what if the bullet gets upset at sonic transition ... it is still farther than most shooters will ever experience.

A typical 22 LR bullet has a very poor BC, a slow twist rate (1:16) and a MV of about 1250 fps ... a combination of all the poor attributes. It will go through sonic transition at about 30 yards but will still be quite accurate well past 100 yards.

The point of the sonic transition concept being ... just because a bullet goes subsonic, it doesn't mean it will turn crazy and do wild things ... in fact it will likely remain stable for a considerable distance downrange before the spin rate decays and it loses stability. The second point is ... even if a bullet went nuts after sonic transition, it is far enough downrange where it really doesn't matter. Bottom line ... sonic transition is way more of a farce than a fact!

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Larry Gibson posted this 27 January 2020

Absolutely incredible the total amount of misinformation regarding the BCs of 55 gr FMJBT bullets, the external ballistics and their stability out of a 12" twist in the above two posts.  

At 3250 fps out of a 12" twist the measured BC of M193 55 gr FMJBTs hovers right at .200.  Secondly, at that velocity, the M193 bullet remains sonic until just after 500 yards.  A lot of very accurate shooting was done with M16/M16A1s at 500 yards by Army, Marine and civilian shooters.  I still shoot a lot of 5.56 loaded with that M193 bullet at 3200 fps out of my 12" twist AR.  I regularly shoot it out to 500 yards with excellent accuracy (for milsurp bullets) and when shooting at 600 yards find the accuracy definitely degraded due to the transition to subsonic.  I have never had, since '65, had any M193 ammunition "tumble" in flight from any M16/M16A1/AR15 and I have shot thousands of rounds out of them. The 1st time I shot a qualification course (stateside with targets that weren't shooting back) with the M16 was in '66 at Fort Campbell.  We shot on the M14 TrainFire qualification course which had targets from 25m to 450m or 500 yards.  The course consisted of 120 shots from foxhole, prone, sitting, kneeling, squatting and standing positions.  I qualified expert then as I did every year during my career.

Thirdly;  the loss of accuracy by a bullet going subsonic became apparent with match shooters shooting 7.62 M118 in M14s and bolt match rifles (most with 12' twists) that had been "Mexican matched" with 168 MKs in the late '60s. Those had muzzle velocities of 2550 - 2580 fps Past 800 yards accuracy went south and 1000 yard scores suffered because they transition to subsonic between 800 and 900 yards.  When loaded to 2700+ fps in a 30-06 in an M1 or bolt match rifle the 168 MK will stay sonic to 1000 yards. 

Lastly; the idea that all bullets will lose stability when going subsonic is baseless.  Only in rare instances or with light weight short bullets for caliber will total stability be lost.  Most often it is accuracy that is lost because the bullet is "buffeted" around a bit and wobbles. Because of that buffeting, not a loss of stability, is why accuracy is lost.  That is why the bullet, after the transition from sonic to subsonic, will "go back to sleep" and fly on it's merry way point forward still stabilized.  Problem is it's direction of flight has been slightly altered so "accuracy" (more correctly; precision) is lost.

How much of a loss of accuracy/precision (or movement away from the original flight path) occurs during the transition to subsonic depends on numerous variables.

LMG

Concealment is not cover.........

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Paul Pollard posted this 27 January 2020

https://appliedballisticsllc.com/2019/11/08/transonic-effects-on-bullet-stability-bc/

This might be a more educated view of the transonic effect. 

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joeb33050 posted this 27 January 2020

https://appliedballisticsllc.com/2019/11/08/transonic-effects-on-bullet-stability-bc/

This might be a more educated view of the transonic effect. 

 

Brian appears to be pimping his book.

The ability to string technical terms into sentences does not substitute for data. I've been looking at this for 20 years or more, and I've not seen any data yet, nor have I seen any simple layman's explanation of what is claimed to be going on.

The only meaningful explanation I've found is this: RPM diminishes with velocity, velocity diminishes with range, stability diminishes with range, at some range/velocity/RPM stability becomes instability and bullets become unstable.The attendant velocity MAY be around the speed of sound.

Proof? take your 22 to the range, some HV ammunition, shoot groups from 50 to 200 yards and look for the transonic instability. I've done it many times. 

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GWarden posted this 27 January 2020

I don't think we can say we will get the same results, or should expect the same if we put .22rf, cast and jacketed bullets together in comparisons. Lots of theories floating around, and those that have "done it" are two different things. My two cents worth. You all have a good day. Again, my thought is only a my theory.

bob

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RicinYakima posted this 27 January 2020

 Ah Ha! Sorry, didn't read the sentence correctly; "Instability" and "larger groups" are not the same. Never had a bullet become unstable dropping from supersonic to transonic to subsonic. But I have unexplained larger groups proportionally from 200 to 300 yards with my 210 grains 30 caliber match load. At 200 it is going 1125 f/s and at 300 it is going 980 f/s. Been through the time of flight, rotational speed, and all the other things I can think of with no positive result.

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joeb33050 posted this 27 January 2020

 But I have unexplained larger groups proportionally from 200 to 300 yards with my 210 grains 30 caliber match load. 

 

Please explain.

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RicinYakima posted this 27 January 2020

JoeB,

Sporterized 1903 Springfield with issue barrel is my Modified Scope rifle. Same rifle, scope and bullet; load between 15.7 and 16.0 grains of 2400 for 1420 f/s. (Depending upon what chrony is being used.) I have records back to 1997.

These are all aggregates of two 10-shot groups. 100 yards 1.211", 200 yards 2.957", 300 yards 6.678". None of these are record setting groups, by the way, but I usually place in the top five. However, there are only three 300 yard data points, as the rest were just shot at practice and not a match.

I would have thought that the 300 yard groups should have been about 6.200".

Ric

 

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joeb33050 posted this 28 January 2020

I GOT SOME DATA FROM AN ACCURATE SOMETNING TEST, AND FROM RFC, LAPUA AND LANDERCASTER.

 

Doubling range increases group size from 2.14 to 2.98 times, avg 2.41 times.2 X 2.41 = 4.82 compare to your 5.514. I don't have enough data, but your group size ratios are in the ball park.

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joeb33050 posted this 28 January 2020

Well, that's wrong. If group size increases 2.41 times as distance increases 2 times, then from 100 to 200 yards group size increases 2.41 times; and from 200 to 300 yards group size increases 2.41 times, total increase is 2.41 squared = 5.808-compare to your 5.514.

Sometimes we add, sometimes we multiply. Sometimes I choose wrong.

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joeb33050 posted this 28 January 2020

--Time of Flight in the "second" hundred yards is greater and therefore

prevailing conditions. wind, have greater effect

---Destabilization effects, especially if twist is borderline sufficient as bullet slows down.

beltfed/arnie

 Wind drift varies as the change in velocity over the range. A bullet with mv = 1000 and 100 yd v of 800 loses 200 fps in 100 yards. Another bullet with mv = 3000 and 100 yd v of 2800  fps is moved the same amount by the wind.

All bullets ant all velocities lose velocity at a diminishing rate with range.

It don't seem right, but it is.

As we toy with ballistic programs, about once a year someone realizes that wind effect lessens as mv lessens, and figures out that 1000 fps means less drift. The announcement is made, sometimes experiments are performed, and guiet ensues.

 

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joeb33050 posted this 28 January 2020

The Houston warehouse guy claimed that group size varied as range. 200 yard groups were twice the size of 100 yard groups.

Yet the Lapua tests, the Landercaster tests and the accurate tests were all in tunnels. Houston? 

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