[Loyac]

Shooting the same 1 oz #8 1200 fps factory load out of two 28" barrel guns, one a 20ga and the other a 12... What constriction would I have to use in the 20ga 391 to get the same diameter of pattern at 40 yards as the 12ga 391 choked IM? Thanks! John

 

[Brian in Oregon]

Get a choke marked IM. And barrel length makes no difference.<br>
<br>
The caveat is that not all individual barrels behave the same, but this would be a general rule and the best place to start.<br>
<br>
The 20ga strings shot more, but if the chokes are made right, they take this into account by being made for pattern.<br>
<br>
If you want actual amount of constriction, you'll have to consult what constriction is being used for 20ga IM.

 

[zzt]

IM

 

[hmb]

The answer to the question is .025 constriction. Give or take a few thousanths either way. You never know for sure. HMB

 

[GordonWood421]

In the "old" days , the amount of choke ; IM , Mod , IC etc ; were defined by the % of shot that would be in a particular circle at a particular distance . Truth be known , the amount of constriction that provided a particular performance may have been different from gauge to gauge . Another train of thought was that it was more related to "area" than to "diameter" at the muzzle .

Regardless , the only real way to determine how a particular choke tube/barrel or fixed barrel performs is to put it on paper . It is amazing as to how some combination is reported by the shooter who has never been near a patterning plate/frame , much less counted the hundreds of holes involved .

Charlie

 

[Loyac]

I thank you all. John