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Sidelock
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I imagine we’re all familiar with these choke percentages from O’Connor’s The Shotgun Book.

30” circle @ 40 yds)
• Full Choke: 70% or higher
• Improved Modified: 65%
• Modified: 55-60%
• Skeet No. 2: 55-60%
• Quarter Choke: 50%
• Improved Cylinder: 45%
• Skeet No. 1: 35-40%
• Cylinder: 35-40

Anyone know if there’s an expanded chart that gives percentages for the chokes at lesser ranges I.e. 35, 30, 25, etc.

If not, taping some of the math minds out there, could those percentages be accurately extrapolated from this 40 yard chart?


Speude Bradeos
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Short answer, no.

Longer answer, is that when looked at from the side (not the front) a shotgun’s pattern looks like a very long trumpet.

The change in width is nonlinear, so, simple algebraic Interpolation would be inaccurate.


If for example, your measured pattern was 40 inches at 40 yards, it would not measure 20 inches at 20 yards.

Last edited by ClapperZapper; 09/18/21 12:20 PM.

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Not pattern % but pattern spread

Field and Stream Sept 1964. I do not have the original article but assume the shells were Winchester/Western Mark 5 with the polyethylene shot collar introduced in 1961. Modern loads are likely better.


…………………………………………YARDS………………………….
.....…….....10…… 15……20……25……30……35……40
CHOKE
Full…………. 9……..12……16……21……26……33……40 inches

Mod……..……12…….16……20……26……32……38……46 inches

Imp Cyl……..15…….20……26……32……38……44……51 inches

Cylinder……. 19……26……32……38……44……51……57 inches


Another

…………………….Approximate Pattern Diameter (Inches)
Choke
..........................10 Yards….......20 Yds….....25 Yds......30 Yds….....40 Yds
Spreader
..............................23............37............44............51............66
Cylinder
..............................20............32............38............44............57
Improved Cylinder
..............................15.............26............32............38............51
Modified
..............................12.............20............26............32............46
Full
...............................9.............16..............21............26...........40

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This should keep you out of trouble 'til the bird season wink

David J. Compton, “An Experimental and Theoretical Investigation of Shot Cloud Ballistics”, 1996
http://discovery.ucl.ac.uk/1382490/1/396689.pdf

E.J. Allen, "Approximate ballistics formulas for spherical pellets in free flight", 2018
https://www.sciencedirect.com/science/article/pii/S2214914717301459

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I didn't read Dr. Drew's links, but we are more interested in pattern percentages at different ranges with different chokes, than we are in the pattern diameter. So far, I think we have to go back to shooting 30" patterns and counting holes. Wow, haven't done that for a while. Drew's Field and Stream charts give us all we really need, without counting holes. Thanks, Drew. On a similar subject, I once had a bunch of 1 1/4 ounce lead fours loaded in AA compression formed hulls, ahead of heavy charges of Unique. I shot them at 40 yards out of a heavily choked Sterlingworth and was amazed at how thick the pattern was. I decided to try the same combination at 60 yards, and found that, even though there aren't a whole lot of shot in a load of 1 1/4 ounces of #4, a teal would have had a hard time getting through that pattern. I can't remember the percentages without looking at the pattern sheets, but they were over the top. I was rather amazed. I kept the pattern sheets and still have them thirty years later. Long story short, I sold the Sterly to a friend who shoots ducks, thinking he would put it to good use. He drilled out the chokes and gave the gun to his son to shoot clay targets. I guess we can't save them all.

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Originally Posted by eightbore
I once had a bunch of 1 1/4 ounce lead fours loaded in AA compression formed hulls, ahead of heavy charges of Unique. I shot them at 40 yards out of a heavily choked Sterlingworth and was amazed at how thick the pattern was. I decided to try the same combination at 60 yards, and found that, even though there aren't a whole lot of shot in a load of 1 1/4 ounces of #4, a teal would have had a hard time getting through that pattern. I can't remember the percentages without looking at the pattern sheets, but they were over the top. I was rather amazed. I kept the pattern sheets and still have them thirty years later. Long story short, I sold the Sterly to a friend who shoots ducks, thinking he would put it to good use. He drilled out the chokes and gave the gun to his son to shoot clay targets. I guess we can't save them all.

Damn .............


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Thirty years later, I still have a few of the lead #4 loads. I also have a few HE Grade Fox shotguns. Maybe I should shoot some patterns and compare them to the Sterlingworth 60 yard patterns.

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See if you can find this: 3/31/2017 Shotgun Sports | Pattern Analysis For Busy Sportsmen by Ron Jones (https://shotgunsportsmagazine.com/archive/mar13/story0313.html) Cites Oberfell and Thompson, The
Mysteries of Shotgun Patterns
(Oklahoma State University Press, Stillwater 1957). Here is a table from the book:

Pattern Percentages for All Degrees of Choke for All Distances
Pattern Percentages Distance in Yards 15 20 25 30 35 40 45 50 55 60
Choke Full 100 100 100 96 82 70 58 48 39 32

Modified 100 100 96 83 71 60 49 39 32 26
IC 100 96 83 71 60 50 41 32 26 21
True Cylinder 98 83 71 59 49 40 33 26 21 17

Rough approximation is you lose 10% every 5 yards after 25 yards.

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Sidelock
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Thank you for posting that link. Here are the charts, which are a bit easier to interpret

[Linked Image from photos.smugmug.com]

[Linked Image from photos.smugmug.com]

I don't have Oberfell & Thompson, but it appears that the data is calculated using mathematical formula rather than having been measured, as is likely the shot spread data I posted.

Compton's study (linked above) discusses 3 dimensional representations of shot cloud phenomena starting on p. 155; and his conclusion:
"It has emerged clearly from this work that it is not possible to produce a satisfactory theory which can predict the downrange behaviour of shot clouds from the muzzle condition in sufficient detail to render practical measurement superfluous. Ballistics therefore have to remain very much an experimental science. Also further work is required to understand the full effects of choke constriction and choke profile on shot clouds."

Oh well - still fun to talk about wink

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I agree that data is not based on real patterns but most likely close enough to be within five yards of real life. From that chart it seems IC at 30 yards would be just as effective as a Full at 40, perhaps more so as 30 yard retained energy is greater. But few seem to know what 40 yards is in shooting situations.

In the world I shoot in most shooters have a very poor ability to accurately estimate ranges. Most reported 45 yard shots are much closer to 30-35 yards. So IC or Mod might be a better choice for most. The few people who can correctly estimate range and correct leads can make shots long past 40 yards. It’s just that 3/4 of them think they can do it, but in reality can’t.

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