doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Forcing cone alterations=out of proof?

I'm not an authority on the subject like some. I just tested using the same barrel with the same loads cutting the cones progressively longer and shooting a gun. I didn't read about other peoples opinions on the subject. So other people likely know more about this than I.

Sherman Bell also did some fairly extensive testing in one of his "Finding Out for Myself" articles in Double Gun Journal. His conclusion was that lengthening the cone without lengthening the chamber did result in some reduction of pressure (usually a few hundred psi) when shooting 2 3/4" shells in 2 1/2" chambers.

LB
Bell's test, of lengthening the forcing cone, was to explore the specific pressure effect lengthening a forcing cone had when shooting an assortment of 2 3/4" shells in an English type 2 1/2" chamber originally with a very short forcing cone .

I'm interested the test parameters of Miller's work on forcing cone effect on patterns and how that compares to what I did.

I did stumble onto Jim Eyster's work from 2010 on forming a radius in the intersection "corner" of the cone and the bore on a 2� cone of a Blaser. My recollection is that a SAAMI cone is 5� (from the bore axis). So the Blaser has "long cones" from the factory. His rounding of the corner showed a significant benefit in pattern performance. What I didn't see in Jim's study was any dimensional description of how big the radius was, etc..
http://www.jimeyster.com/testing/documents/Forcing%20Cone%20Test.pdf

Actually Chuck, it had two purposes. One was to determine the pressure increase (if any, and there was always at least some increase) when firing various 2 3/4" shells in a 2 1/2" chamber, and then to see what would happen with the same loads when just the forcing cone (but not the chamber) was lengthened.

LB,
I was addressing only the lengthened cone tests, but you are obviously correct that he tested 2 3/4" shells in a 2 1/2" chamber first.

I had forgotten I had a somewhere acquired a pdf of ANSI/SAAMI Z299.2-1992, American National Standard Voluntary Industry Performance Standards for Pressure and Velocity of Shotshell Ammunition for the Use of Commercial Manufacturers. It shows a 5 degree (from bore axis) cone angle and a reference dimension that comes out to about a .417 cone length. The Blaser that Eyster tested and stated was a 2 degree cone angle would come out to about 1" long.

In my earlier statement about what I had tested, I mistated what I had tested. I tested standard SAAMI cone vs. approx 1 1/2" long cones and an approximately 4" (36 minutes of angle) long cone (not 3" as stated earlier),all in one 3" chambered 12 ga gun using 2 3/4" target shells. The 1 1/2" cone was cut with a reamer from Brownells, and the 4" cone was cut with a "taper-pin" reamer from a tool supply house and specially ground to fit inside the 12ga chamber by a professional cutter manufacturer who is a friend.

I have also tested an approximately 3" long cone in .410 3" chambers using 3" shells. I have tested at least 4 possibly as many as 6 separate .410 guns with before and after. I saw a benefit to the patterns.

Very interesting stuff, Chuck. Thanks.