Indians For Guns

Understanding Choke
---------------------------

This calculation for choke based on markings helped a lot.

*For older English / Belgium / German Guns
If it says 181, 182 etc that is the same as 18.1 or 18.2 mm
So

divide the measurement by 254 (no idea why 254)
so 18.2/254 =.0716

then (729 = 12 guage normal bore)

so .729 - .716 = .013 is the constriction measured in thousandths of an inch.
From - http://www.hallowellco.com/choke_chart.htm

12 Gauge 20 Gauge 28 Gauge .410" Bore American English Browning Italian Perazzi Percentage
Constriction Constriction Constriction Constriction Designation Designation Codes Codes Codes Pattern
.000" -.001" .000" - .001" .000" .000" cyl true cylinder *** C**** 0 40%
.002" - .006" .002" - .004" .001" - .004" .001" - .002" skeet impr cylinder **$ S 1 45%
.007" -.013" .005" - .011" .005" - .007" .003" - .006" imp cyl quarter **- **** 3 55%
.014" -.023" .012" - .019" .008" - .014" .007 - .012" mod half ** *** 4 60%
.024" -.031" .020" - .026" .015" - .020" .013" - .017 " imp mod three quarter *- ** 6 65%
.032" -.040" .027" - .033" .021" - .027" .018" - .021" full full * * 9 70%
.040"+ .034"+ .028"+ .022"+ ex. full 10 75%


Please check the below link for other information

http://www.guncustomizing.com/tech.htm
has useful info on -
Backboring
Chokes
Forcing Cones
Patterns
Standard Shot Chart
Shotgun Velocity Variations with Different Barrel Lengths

Hope this helps
/S/

254 because 25.4 mm in an inch and 729 because diameter of a 12 bore is .729 inches.
And it should be 25.4 not 254.
thats why you got .0716.
If you had used 25.4 you would have got .716.

254 should be used if you are usind 181,182 instead of 18.1 or 18.2

All one needs to do is use same units.

Ah good. the final piece of the puzzle just fell into place.
Thanks Shooter - Naam bhi shooter aur kaam bhi shooter - wah

/S/

Naam bhi shooter aur kaam bhi shooter

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