12G Shotgun Choke Data

[PieFace]

I was wondering if anyone knew, had access to, or knew of any publication which showed the detailed dimensions of 12G shotgun chokes?

I'm looking into making some experimental cylinder chokes to fit the Benelli M4 which are in effect little more than barrel extension. I think I'm correct in saying the thread for the M4 choke is 44tpi double start (could be wrong on that), I know you can purchase the reamers and taps to cut the internal thread for the barrel.

I'm faced with the problem of cutting the external thread for the choke and although I know the pitch the thread profile is still unknown 60 degress, 55, 50 who knows?

Any advice if you know this information or know of a book containing it would be most welcome.

Steve...

 

[oneounceload]

You could always buy one that fits and reverse engineer it

From there, here's a chart showing the constrictions:

http://www.hallowellco.com/choke_chart.htm

 

[PieFace]

I had considered this as an option but if the dimensional data is out there, and it must be somewhere, it would make my job considerably easier.