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Almost Everything You Ever Wanted To Know About Shotgun Chokes




NYECOGunsmith

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#1
But didn't know who to ask.
Since there is a discussion going on in another area of the forum on shotgun chokes, I thought I should probably post this up here as a reference.


Shotgun chokes are a constriction in the barrel of a shotgun through which the shot string must pass before it exits the muzzle. This amount of constriction is a constant, no matter what the gauge or bore of the shotgun.

Here are the now standard constrictions for the various chokes. You would subtract the constriction from the nominal bore diameter to find what the exit diameter of the barrel would be, or , conversely, you could measure the exit diameter, subtract it from the nominal bore diameter and determine what the choke is if the barrel or choke tube is not marked.

The constrictions presented below are in the order of increasing constriction, from no constriction to most constrictive. Their abbreviations are also shown, along with the number of dots, notches, or Stars, or other physical markings that are used to identify them. Not all choke sizes utilize this method of identifying their constriction, just the more common sizes as you will see.

Cylinder bore = the nominal bore of the gauge or bore you are dealing with. Five Notches, Dots or Stars.
Skeet1 = 0.005” No dots/notches etc.
Skeet2 = 0.0075” No dots/notches etc.
Improved Cylinder = 0.010” 4 Notches, Stars or Dots
Light Modified (LM) = 0.015” No dots/notches etc.
Modified (M) = 0.020” 3 Dots, Stars or Notches.
Improved Modified (IM) = 0.030” 2 Dots, Notches or Stars
Light Full (LF) 0.035”, No dots/notches/stars, etc.
Full (F) = 0.040” 1 Star, Dot or Notch
Improved Full = 0.050” No dots/notches/stars, etc.
Extra Full (EF) = 0.060” No dots/notches/stars, etc.
Turkey Full (TF) = 0.080” No dots/notches/stars, etc.
Super Full (SF) = 0.10” No dots/notches/stars, etc.

Standard bore diameters for today’s most commonly encountered shotgun chamberings, in case you are interested, run as follows. Some of these may be chamberings you have never seen or heard of, those are ones that are either antiquated now, or are still found in Europe and other parts of the world. At one time or another I have handled/fired/ or worked on a shotgun for each of the chamberings I have listed below.

4 Gauge = 1.052 “ Ø
8 Gauge = 0.835” Ø
10 Gauge = 0.775” Ø
11 Gauge = 0.750" Ø
12 Gauge = 0.729” Ø
13 Gauge = 0.710" Ø
14 Gauge = 0.693" Ø
16 Gauge = 0.662” Ø
18 Gauge = 0.637" Ø
20 Gauge = 0.615” Ø
22 Gauge = 0.596" Ø
24 Gauge = 0.579” Ø
28 Gauge = 0.550” Ø
32 Gauge = 0.526” Ø
36 Gauge = 0.506” Ø
40 Gauge = 0.488" Ø
.410 Bore = 0.410” Ø

If you take information from the two above data bases, you can figure out what your gun is choked as, if you don’t know.

For example, if you measure a bore exit diameter of 0.689” Ø, you could be reasonably sure that the gun is choked Full, and should pattern close to the percentages I will give you next.

Why do we have chokes you might ask? Well because they serve to alter the pattern of the shot, to keep as many of the pellets in the shot load within a given area at a given distance.
Normally, we pattern a shotgun by shooting at a 30” Ø (Diameter) circle at various distances.
For Skeet for example, we would use a distance of 20-25 yards. Most folks choose the 20 yard mark for skeet.
At that distance, a Cylinder bore choke (that’s no choke whatsoever) would put 80% of the total number of pellets contained in the shot charge into a 30”Ø circle.
At 30 yards with this same choke, we would only get about 60%, and at 40 yards, 40%.

At these same distances, 20,30 and 40 yards, we could reasonably expect to see the following percentages for the following chokes. These are just rough estimates, as the percentage will vary by load, shot size, shot hardness, buffering of the shot, wad type, barrel length, velocity, and a number of other factors.
Remember, just because your gun produces a certain percentage pattern with one brand of shell, does NOT mean it will produce the same pattern with another maker’s shells, even if the shot size, charge weight, velocity, etc. are the same. No way to know unless you pattern all of them on the patterning board!

Cylinder 80%, 60%, 40%
Skeet1 90%, 70%, 50%
Improved Cylinder should give us: 100%, 75% and 55%.
Modified should yield 100%, 85%, 60%
Improved Modified gives us 100%, 90%, 65%
And a Full choke hopefully should pattern 100%, 100% , 70%.

There are other choke constrictions of course as I noted waaaay above, and they will alter the above percentages.

That’s the basic of Chokes in a shotgun, any questions drop me note or post a reply here.

Oh, and should you be interested, here's a chart that shows how many lead pellets are in an ounce of each of the commonly used shot sizes. Stole this one from Wikipedia, and it would take too long to type up from my notes.

Size Nominal diameter Pellets per oz (28 g) Quantity per lb.[3]
Lead Steel
FF .23" (5.84 mm) 35
F .22" (5.59 mm) 39
TT .21" (5.33 mm)
T .20" (5.08 mm) 36 53
BBB .190" (4.83 mm) 44 62 550
BB .180" (4.57 mm) 50 72 650
B .170" (4.32 mm)
1 .160" (4.06 mm) 72 103 925
2 .150" (3.81 mm) 87 125 1120
3 .140" (3.56 mm) 108 158 1370
4 .130" (3.30 mm) 135 192 1720
5 .120" (3.05 mm) 170 243 2180
6 .110" (2.79 mm) 225 315 2850
7 .100" (2.54 mm)
7½ .095" (2.41 mm) 350 3775
8 .090" (2.29 mm) 410 686 5150
8½ .085" (2.15 mm) 497
9 .080" (2.03 mm) 585 892 7400

OK, I forgot to give all ya'alls a bit more Choke information, and that is, which screw in chokes will fit in what guns. So here is a choke interchangability chart, with thanks to Carlson Chokes ®

American Arms: Interchanges with Fausti/Traditions shotguns style threads
Baikal/European American Arms: Interchanges with Standard Tru Choke style threads
Benelli: (Current production-square threads) Interchanges with Beretta style threads
Benelli Sport Crio System: Interchanges with Beretta Optima style threads
Beretta: (Current production) Interchanges with Beretta style threads
Beretta: (Old style-no threads-uses muzzle cap) No known Interchange
Beretta Optima: Interchanges with Optima threads (Models 682E and DT10)
Beretta Optima Plus: Interchanges with Optima Plus threads (Models 391A Extrema)
Bernardelli: No known Interchange
Browning Invector: Interchanges with Winchester, Mossberg 500, Weatherby, Maverick 88, Smith and Wesson and Savage Guns style threads
Browning Invector Plus: Interchanges with Browning Invector Plus, Winchester Super X2 and Winchester Supreme style threads
Century Arms (Arthmies and Centurion Models): Interchanges with Berreta and Benelli style threads
Charles Daly: Current Production pumps and semi-autos interchanges with Remington Style threads
Charles Daly: Current Production O/U, Interchanges with Winchester style threads
Churchhill 12 ga: Interchanges with Fabarm style threads, some models American Arms style threads
Fabarm: 12 ga. Interchanges with Fabarm style threads
Franchi: (Current production-square thread) Interchanges with Beretta/Benelli style threads
Franchi: (Old Style-v threads) Interchanges with Fran Choke style threads
Ithaca: (Old Style-Fine threads) Interchanges with Tru Choke style threads
Ithaca: (New Style 12 ga.) Interchanges with Winchester style threads
Ithaca: (All New Style 20 ga.) Interchanges with Tru Choke style threads
Laurona (O/U): Interchanges with American Arms style threads
Luger: No known Interchange
Marrochi Golden Snipe Field O/U: Interchanges with Browning Invector Plus style threads
Maverick Model 88: Interchanges with Mossberg 500, Winchester, and Browning Invector style threads
Miroku: Interchanges with Winchester style threads
Mossberg 500: Interchanges with Winchester, Weatherby, Browning Invector, and Maverick 88 style threads
Mossberg 835 and 935: Interchanges with 835 Mossberg style threads
Mossberg 9200: Interchanges with Mossberg 500 style threads
Remington: Interchanges with Remington and Charles Daly
Ruger Older Models: Interchanges with Winchester style threads (Short chokes)
Ruger SC Newer Models: Interchanges with Ruger SC style threads (Long chokes)
Sako/Tikka 12 ga.: Interchanges with Browning Invector Plus style threads
Savage: Interchanges with Winchester and Mossberg 500 style threads
Silma: No known Interchange
SIG Arms: No known Interchange
SKB Short Style: Interchanges with Winchester and Mossberg 500 style threads
SKB Competition: Interchanges with SKB Competitor style chokes
Smith and Wesson: Interchanges with Winchester, Mossberg 500, and Browning Invector style threads
Stevens and Savage Model 411: Interchanges with Tru-Choke or Baikal style threads
Stoeger 2000 Semi-Auto: Interchanges with Beretta and Benelli style threads
Stoeger Condor (O/U): Interchanges with Winchester style threads
Stoeger Luger (O/U): Interchanges with American Arms style threads
Stoeger Uplander (Side by Side): Interchanges with Winchester style threads
Traditions by Fausti: Interchanges with American Arms style threads
Traditions Semi-Auto ALS2100: 12 ga. Interchanges with Berretta style threads
20 ga. No known Interchange
Thompson Center: Interchanges with Winchester style threads
Tri-Star 411 and TR11: Interchanges with Rizzini style threads
Tri-Star Phantom Field & Model 380D: Interchanges with Beretta style threads
Tri-Star Phantom HP: No known Interchange
Tri-Star Silver Series: Interchanges with American Arms style threads
Valmet: No known Interchange
Verona LX O/U: No known Interchange
Verona SX Semi-auto Models: No known Interchange
Weatherby: Interchanges with Winchester, Mossberg 500 and Weatherby style threads
Winchester: Interchanges with Winchester, Mossberg 500 Weatherby and Browning Invector style threads
Winchester Super X2 & Supreme: Interchanges with Browning Invector Plus style threads

And lastly, from my own records, here are some screw in choke dimensions, for the really twisted minds who want to know.
Browning Invector Plus = .820"-32 TPI
Browning Invector = .812"- 32 TPI
RemChoke = .814"-32 tPI
Tru Choke =.795"-44 TPI
Thin Wall = .775"- 44 TPI
 
Last edited:

RepairMan

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#2
If there were such things as vulcan mind melds... There would be a line around the block to grab the info if your head...
 

NYECOGunsmith

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#3
If there were such things as vulcan mind melds... There would be a line around the block to grab the info if your head...
A good part of it is still classified, ya'all would have to kill yourself as soon as you thunk those thoughts!

The rest of it is just a lifetime's accumulation of useless, semi-useless and almost useful bits of junk.
 

Tophog

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#4
Steve, don't you ever run out of numbers? :glare:
 

rat907

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#5
A good part of it is still classified, ya'all would have to kill yourself as soon as you thunk those thoughts!

The rest of it is just a lifetime's accumulation of useless, semi-useless and almost useful bits of junk.
So the undesclosed, super secret organization, funded off the books with questionalbe funds haven't applied neuro-blockers to hide these thoughts from your memories upon your retirement/deactivation, Steve? How manchurian canidate of them.

If I had half the recollection and organization you possess, even a tenth of it, I would be a genius instead of a half-wit spewing psyco-babble to any whom listen.
 

GetRealLV

Well-known member (45 ACP)
#6
Steve, thank you for the info. As always you seem to provide useful info when I need it.

Questions:
I am considering having my Mossy 930 SPX barrel threaded for chokes. At this time the factory bore produces a pretty wide pattern even at 20 feet. Are there more desirable choke brands? Will I still be able to shoot slugs, 00 buck and #4?

I found a gentleman in KY that will do it with three a different 3 choke deal with threading and 3 choke tubes (Full, Modified, and Improved Cylinder) for $109 including return shipping. It appears that this person has a great deal of positive feedback. He uses either standard Mossberg or Rem-Chokes.

Thanks for any input!
 

NYECOGunsmith

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#7
Steve, thank you for the info. As always you seem to provide useful info when I need it.

Questions:
I am considering having my Mossy 930 SPX barrel threaded for chokes. At this time the factory bore produces a pretty wide pattern even at 20 feet. Are there more desirable choke brands? Will I still be able to shoot slugs, 00 buck and #4?

I found a gentleman in KY that will do it with three a different 3 choke deal with threading and 3 choke tubes (Full, Modified, and Improved Cylinder) for $109 including return shipping. It appears that this person has a great deal of positive feedback. He uses either standard Mossberg or Rem-Chokes.

Thanks for any input!
After your barrel is threaded, as long as you always remember to never fire it, (or clean it) without a choke installed, it will do everything your original barrel would.
For slugs and buck shot, put in a fairly open choke, like the Cylinder Bore (CYL) choke, the Improved Cylinder (IC) or a Skeet choke (SK). For the #4 and up shot sizes, you can use any choke tube from Cylinder all the way through the Super Full.

That's a great price for that work, could you drop me a PM with his name and contact info, I think I may know the gentleman from years gone by, if so, I can give you feed back on him. If it is my old friend, he does great work.

I should have listed a chart with Choke Interchangeability on the first page of this thread, I will fix that in a moment, sorry for the lack of foresight!
 

NYECOGunsmith

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#8
Steve, don't you ever run out of numbers? :glare:
Nope, I get them in bulk from the spin doctors in D.C., same way the pollytishuns do. :reaction:
 

NYECOGunsmith

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#9
So the undesclosed, super secret organization, funded off the books with questionalbe funds haven't applied neuro-blockers to hide these thoughts from your memories upon your retirement/deactivation, Steve? How manchurian canidate of them.

If I had half the recollection and organization you possess, even a tenth of it, I would be a genius instead of a half-wit spewing psyco-babble to any whom listen.
Actually Denny, when they went to hit me with the Neuralizer when I retired, the cheap chinese batteries in it were almost dead, so all it did was make me forget ,,,,,,,,,,,,uh,,,,,,,something that wasn't worth remembering anyway.


Specs called for American Made Dura Cells®, but some Pollytishun had connections to PRC and got kick backs, so cheap chinese batteries were in it, and it didn't do the full erase it should have.

Besides, the bastiches call at least once a month with some problem for me to solve, or trying to get me to come back to work.

All the gear I designed, I left behind volumes of material on its design, and how to diagnose and repair any conceivable malfunction.

But do they ever read the manual(s)? NOOOOOO, its easier to pick up the phone, whine and moan a bit and get me to finger it out for them. At least they pay their bills on time, MOST of the time.

And I have yet to hear you spew psycho babble. Your information is always useful, and accurate. You just type with an accent is all, probably due to your childhood spent in the frozen north!
 

GetRealLV

Well-known member (45 ACP)
#10
"That's a great price for that work, could you drop me a PM with his name and contact info, I think I may know the gentleman from years gone by, if so, I can give you feed back on him. If it is my old friend, he does great work."

PM Sent as requested!

Thanks Steve!

Barry
 

NYECOGunsmith

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#11
That's a great price for that work, could you drop me a PM with his name and contact info, I think I may know the gentleman from years gone by, if so, I can give you feed back on him. If it is my old friend, he does great work.

PM Sent as requested!

Thanks Steve!

Barry
Thank you Barry!
This is not the name I was expecting, was expecting Dave (David) Rose, this might be his son or a relative, don't know for sure. Will have to look up the address I had for Dave and see if its the same. If it is Dave's son, his work should be as good as his Dad's, which was superb.
 

NYECOGunsmith

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#13