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Joined: Mar 2009
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Boxlock
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Boxlock

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I have several guns that have more than one number stamped on the same barrel. Did someone change the choke?
Anyway, Does anyone have a link where I can decifer the chokes?

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Make? Model? Date of Mfg.?

There is no "standard" all were different.


Mark
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Chokes actually are the difference between actual bore diameter and choke diameter. Named "chokes" (i.e. IC, Mod, full, etc) will vary from one barrel to another from the same maker. They also could have been altered at some time. You need to actually measure what each individual barrel is and subtract the two readings to determine your real choke.

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This is from my files, I saved it from a earlier post. Reprinted without permission.
Tyler


Here is a copy of something I put together in response to a similar question on another BB.
The traditional way of designating chokes (before the advent of interchangeable choke tubes) was by the patterns they produced. Don Zutz says (in a chapter of Lyman's 4th Ed.) that all pattern percentages are measured in a 30" circle at 40 yards, except for the .410 bore, which is measured with a 20" circle at 20 yards. He cites the following percentages as "industry standards" without specifically naming SAAMI.

Cyl 40%, Skt 45%, IC (British 1/4 choke) 50%, Skt 2 (often called light Mod, Brit 3/8) 55%, Mod (Brit 1/2) 60%, IMod (Brit 3/4) 65%, Full (British "choke") 70%, Ex F 75%.

Every combination of gun, choke tube, and shell may produce a different percentage, so many manufacturers of choke tubes have adopted constriction designations instead of percentage designations. I really don't know if the manufactureres are consistent (I suspect they are not) but the famous shotgun gunsmith Ralph Walker listed the following constrictions in The Gun Digest Book of Shotgun Gunsmithing, 1983.

12 GAUGE: Skt .005, IC .009, Skt2 .012, Mod .019, IMod .025, F .035. These are close, but not quite the same as Briley's specs, as printed on the back of a business card (about 1998 vintage) from Stephen Power, Sales Manager, which are as follows: Sk .005, IC .010, LM .015, Mod .020, IMod .025, LFull .030, F .035, XF .040. It looks like Briley has simply rounded off the numbers for the sake of convenience.

Continuing now with Walker's data:

16 GAUGE Sk .004, IC .007, Sk2 .010, Mod .015, IMod .020, F .028

20 GAUGE Sk .004, IC .007, Sk2 .009, Mod .014, IMod .019, F .025

28 GAUGE Sk .003, IC .005, Sk2 .007, Mod .012, IMod .016, F .022

.410 Bore IC .004, Mod .008, F .017

Now I am begining to wonder why I went to the trouble of looking up all this data and typing it. I guess it is because I am an engineer by birth as well as by education, and engineers just love data. I have been suffering from data withdrawal since I retired. I hope someone finds it usefull. You might want to copy this response and save it as an MSWord or WordPerfect document, for future reference. I will, because I don't want to have to get my data fix this way again!

Jim Cassada (No, I am not Jim Casada, the writer/editor!)

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Here's a link to Briley's Choke Chart:

http://www.briley.com/2009/chokeconstrictions.html

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What would the equivalent choke constrictions be for a 10 gauge?

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Here's Colonial Arms Choke Chart for 10,12,16,20,28-ga's. and .410 caliber as well as true bore diameters for each:
http://www.colonialarms.com/chokespecs.html

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Originally Posted By: bamboozler
Here's Colonial Arms Choke Chart for 10,12,16,20,28-ga's. and .410 caliber as well as true bore diameters for each:
http://www.colonialarms.com/chokespecs.html


That is a good reference to go by, but some manufacturers of 16 ga, especially L.C. Smith, the bore of pre-1930's guns is .650, changed to .662 after that along with chamber length.

The other thing is, without knowing bore size, choke diameter means nothing. Actually the only way to know what your choke is, is to shoot 5 rounds at a pattern board, choke size means nothing until then they are just numbers.

Last edited by JDW; 03/25/09 06:18 PM.

David


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Old bbls designed for card wadding usually had the bore area (not dia) reduced to a range of 89-90%, thus √(90%.729²) =.692 or .037" constriction. Plug in any other dia you desire. Later guns for more efficient wadding open this to a reduction more on the order of 92%. This gives a dia of .699" or .030" constriction from the standard .729" for 12ga.


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Originally Posted By: bamboozler
Here's a link to Briley's Choke Chart:

http://www.briley.com/2009/chokeconstrictions.html



Is there any reason why Briley has the same dimensions for 20 and 28? I've pointed this out before but none had an answer.

I have always preferred Colonial's.


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