GROUP SIZES, 100 AND 200 YARDS

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  • Last Post 23 January 2018
joeb33050 posted this 17 January 2018

 

GROUP SIZES, 100 AND 200 YARDS

 

Jacketed bullets are more accurate than cast bullets.

 

We might be able to find out why by examining the differences.

 

200-yard group sizes are more than two times 100-yard group sizes.

 

The ratios of 200-yard to 100-yard group sizes for CBA NM 1999-2017, and IBS/NBRSA NM 2017 are:

 

                                5-SHOT                 10-SHOT

 

CBA                        2.25                        2.36

 

 IBS/NBRSA         2.44                        2.55

 

Jacketed bullets shoot much smaller groups than cast, but the ratios of 200-yard to 100-yard group size are larger for jacketed bullets.

 

There are at least these notions about what’s happening:

 

200-yard groups should be twice the size of 100-yard groups, but;

 

The sideways, (perpendicular to flight path), acceleration of the bullet from 0 to 100 yards gives the bullet a sideways velocity that still operates from 100 to 200 yards, and

 

The forces that cause that sideways acceleration continue to operate from 100 to 200 yards.

 

Maybe when we understand the difference in these ratios, we’ll get a clue about the accuracy differences.

 

joe b.

 

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RicinYakima posted this 17 January 2018

Last year someone proposed (Ken?) that the difference was equal to the time of flight of the bullet. The bullet's velocity is slowing quicker between 100 and 200 than between 0 and 100. Jacketed bullets are usually much shorter for caliber than cast bullets and slow down faster than cast also because of wind resistance.This increased time allow for the "lateral" acceleration to take place longer. Just a thought for your consideration. Ric, the guy who ain't no math wiz.

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John Alexander posted this 17 January 2018

I don't know if this will help or hinder the discussion but here goes.

The lateral acceleration (from unbalanced bullets, imperfect barrel and crown, lateral twitches of the gun as the shot is fired, barrel vibration, etc} ends at the muzzle. No more acceleration. but  that acceleration has given the bullet a diminishing lateral velocity for the rest of the trip  (average lateral velocity between A&B x time between A&B  = deflection at B from these causes.

The lateral velocity is very low compared to the velocity toward the target (axial?) so slows very little to none compare to the slowing of the axial  velocity.  So by the Ken/Ric principle, the almost constant lateral velocity moves the bullet more between 100 and 200 than between 0 and 100 because it has more time.

Any wind will cause additional deflection. Any lateral vector of force by the wind WILL cause a lateral bullet acceleration resulting in additional, and increasing lateral velocity, and additional deflection adding to the type of deflection above.

If the wind is constant over 200 yards, this average lateral velocity between 0 and 200 will be a bit over twice as big as between 0 and 100 because it has a bit more than twice as much time.  And because 2 (average velocity)  X  2+ (time of flight) = 4+ (deflection @ 200.)

So wind deflection is about 4 times as much at 200 than at 100 and the other types of deflection goes up by more than two.

Both of these types of deflection tend to make the deflection at 200 somewhat more than than double. Hope I have all this straight and it makes sense.

Not sure what we can make of this in the comparison between CB and JB -- maybe nothing?

John

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Ken Campbell Iowa posted this 18 January 2018

ric ... minor point ... i think the bullet slows faster between 0 and 100 than between 100 and 200 ... i think that is what you meant .  higher headwind ...

ken

 

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John Alexander posted this 18 January 2018

 I revised my sixth paragraph.  I think it reads correctly now.

John

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RicinYakima posted this 18 January 2018

Ken, correct poor sentence structure: bullets slows faster from 0 to 100,but takes longer from 100 to 200. i.e. time of flight.

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joeb33050 posted this 18 January 2018

Wind deflection is a function of velocity loss, not time of flight. I don't think that the 200/100 group size ratio has much to do with wind.

An older paper:

 

WIND DRIFT AND WIND COMPENSATION

            Shooters compensate for the wind by watching wind flags and holding off. If, for example, the wind flags show that there's more wind from the left than during previous shots, the shooter will aim slightly right of where he aimed during previous shots.

             We assume that this compensation is effective; measurement of that effectiveness is difficult.

             Perhaps, I thought, some measurement of wind compensation effectiveness by shooters is lurking in the data.

             Group sizes at 200 yards are greater than 2 times 100-yard group sizes. For the 506 CBA National Match records from 2000-2013, 5 shot groups at 200 yards are 2.236 times the size of 5 shot groups at 100 yards. The ratio for 10 shot groups is 2.385.

            "Wind", here, is whatever causes this. Wind drift is one of the causes; maybe light changes or bullet velocity variations are others. Note that with no Wind, 200-yard group sizes will be just twice 100-yard group sizes.

            We expect shooters to shoot smaller groups; and smaller groups to indicate better shooters.

            We expect better shooters to compensate for the wind more effectively. A shooter who compensates for the wind perfectly would shoot 200 yard groups just twice he size of 100-yard groups.

            Then we expect group size and the ratio of 200/100-yard group size to be directly related. Smaller group shooters should have lower ratios.

            I fully expected the slope of the chart of group size and ratio to be a measurement of the effectiveness of shooter compensation for wind.

            Cast Bullet Association, (CBA), National Match data from 2000-2012; and IBS 2011 and 2012 Group National data was analyzed.

            The only trend lines that I could find on any chart was using 5 shooter moving average data.

            For CBA 5 PBB, HV, PRO and UNR and 10 PBB, HV and PRO matches there is no pattern on the charts.

            For CBA 10 UNR there is a trend line upward.

For IBS 2011 HV, LV, SP and U matches; and IBS 2012 SP and U matches there is no pattern on the charts.

             On the IBS 2012 HV chart there is a trend line upward.

 On the IBS 2012 LV chart there is a trend line upward.

                   There's nothing I can find that's a convincing argument for a relationship between group size and the 200/100-yard group size ratio. The trend lines are few, and not very clear. If better shooters compensate for the wind more effectively, I can't prove it using the available data.

 

 

 

            What does it mean, if anything?

 

            I still believe that better shooters compensate for the wind more effectively.

 

I think that Wind does not have a very large effect on accuracy, and that there are other variables affecting accuracy that have greater effect and operate to mask the trend lines and confuse the analysis and analyst.

 

 

joe b.

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Paul Pollard posted this 18 January 2018

An older paper:

 

WIND DRIFT AND WIND COMPENSATION

            Shooters compensate for the wind by watching wind flags and holding off. If, for example, the wind flags show that there's more wind from the left than during previous shots, the shooter will aim slightly right of where he aimed during previous shots.

 

This should make that shot go farther right, and out of the group a little more, to the right.

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joeb33050 posted this 18 January 2018

An older paper:

 

WIND DRIFT AND WIND COMPENSATION

            Shooters compensate for the wind by watching wind flags and holding off. If, for example, the wind flags show that there's more wind from the left than during previous shots, the shooter will aim slightly right of where he aimed during previous shots.

 

This should make that shot go farther right, and out of the group a little more, to the right.

I put these intentional errors in to see if anyone reads the paper. Congratulations, you and John seem to be of the few.

joe b.

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RicinYakima posted this 18 January 2018

There once was an old Fire Department Captain who liked to "teach" the firefighters to take better care of their equipment. So he would put grease on their boot soles, take the thermal lining out of the their turnout coats, etc. etc. So one day we where on the second floor of an industrial building fire. When he turned on the air bottle for his breathing apparatus, why the bottle was empty. The smoke was down to street level by the time he crawled down the stairs, puking his guts out. Nobody seems to have helped him until the ambulance guys put him in the back for oxygen. FWIW

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Ken Campbell Iowa posted this 18 January 2018

"""  Note that with no Wind, 200-yard group sizes will be just twice 100-yard group sizes. """

??

ken sez:  i think only if the groups have zero dispersion .    the dispersion vector is in relation to time of flight, not distance of flight .

it might be interesting to look at the two times of flight ...

0 to 100 yds.    and

0 to 200 yds. 

is it 2.24 longer ?? 

ken

 

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Paul Pollard posted this 19 January 2018

No, it is not that ratio. From the Cast Bullet Handbook, 3d Edition. Velocity affects drift, too. The TOF multiple shows only a little more than 1. They are almost equal in time of flight.

Time of Flight

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Larry Gibson posted this 19 January 2018

"""  Note that with no Wind, 200-yard group sizes will be just twice 100-yard group sizes. """

??

ken sez:  i think only if the groups have zero dispersion .    the dispersion vector is in relation to time of flight, not distance of flight .

it might be interesting to look at the two times of flight ...

0 to 100 yds.    and

0 to 200 yds. 

is it 2.24 longer ?? 

ken

 

At 200 yards I get an additional .75 bullet drift to the right with the 314299 at 1830 fps.  Bullet drift is not the same as wind drift.  If the wind is coming from the left I have to account for the added bullet drift.  If the wind is from the right I have to subtract for the bullet drift plus there is a bit of bullet rise. 

 

LMG

 

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

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MarkinEllensburg posted this 19 January 2018

Interesting discussion. All I can add is that I have noticed that the wind does not seem to prevent "good" groups where I shoot. I use a wind flag or two but do not change my point of aim, a skill I've yet to acquire.The wind although hard to measure based on the range design is nearly omnipresent and in excess of 20mph sustained often enough.

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Larry Gibson posted this 20 January 2018

Range conditions can definitely have a big influence on group size and score.  At the bench rest range I shoot matches at (Ben Avery Complex, Phoenix, AZ) it is a large barren rock and sand 300 yard range.  There are no trees along the sides or on the hill behind the impact area.  During the Military Rifle matches wind flags are not allowed.  There is not anything to judge the wind by.  With the low humidity even mirage is not usable.  The best you can do is go by feel and the little dust other shooters bullets kick up down range.  Even then the wind is not consistent and switches all the time.

I was told when I first started shooting there; "there will be no records set on this range!"  After having shot there for numerous matches I would not place any bet against that.......what fun!

LMG

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

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R. Dupraz posted this 20 January 2018

Two of the best scores that I have ever shot were with no wind flags. One was with the BPCR, 45x2.4 Sharps at a long range gong match near Alliance, Neb, 200 to !000yds. The other was a CBA military match at the Hawkeye club range, Sioux City, Ia. 

All I did was simply pay attention to  the feel of the direction, intensity and change of the breeze / wind against my face and neck. And either fired in a like condition or made the appropriate correction. It was surprisingly effective and accurate.

And no, I don't have any data. 

 

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Maven posted this 20 January 2018

"And no, I don't have any data."  ...RD 

There's a special place in hell for you, RD. (LOL!!!)

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frnkeore posted this 20 January 2018

Something that I've found, that not many people take into account, when they talk about wind drift, is that the most significant thing, is the amount of velocity lost or more accurately the percentage of velocity lost.

ToF doesn't directly correlate to wind drift. One of the best ways to address WD, is to increase the BC of a bullet, there by decreasing the percentage of velocity lost. Jacketed bullets do have a huge advantage, in that regard.

Check it out on a ballistic calculator. Increase BC alone, you'll see that wind drift decreases more for less velocity lost, compared to ToF. Theoretically, if a projectile doesn't loose any velocity, it won't have any WD but, can have lots of Tof.

That's why that I've always been a advocate of spitzer bullets and high SD bullets. It's a little harder to get a spitzer to shoot well but, well worth it.

Frank

 

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R. Dupraz posted this 20 January 2018

"And no, I don't have any data."  ...RD 

 

There's a special place in hell for you, RD. (LOL!!!)

 

Not positive but I think I've just been offended! undecided

 

 

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RicinYakima posted this 20 January 2018

But then again, maybe not!

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joeb33050 posted this 20 January 2018

And no, I don't have any data. 

And proud of it.  Thank God that you're not involved  in anything important.

Are you from Alabama?

joe b. 

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