Hello 8B,
Here are some quotes from the article related to different tests involving a
comparison of same shells before and after the lengthening:
"Modifying the 2,5 inch chamber with a long forcing cone dropped the breech pressure slightly to 11,045 psi (from 11.125 psi), The pressure at the cone dropped more significantly to 7500 psi (from 8,100 psi), or almost down to 2,75 inch pressure value."
"When the long-coned figures are in, we see a drop of only 220 psi, to 8545 psi at one inch but again, a nice fall-off of 800 psi to 5500 psi at the forcing cone."
"The much-anticipated data with the long forcing cone was a pleasant surprise. The breech pressure returned to 6385 psi, virtually identical to the longer chamber figure. At the front of the chamber the number is 4700 psi, which is even lower than in the long chamber".
But, having re-read the article I must now keep in my memory bank (don't know for how long it will stay) Mr. Bell's last remark:
"But I might have the forcing cones lengthened, assuming the barrel wall thickness will allow it. I wouldn't bother for the slight pressure benefit but as a fussy handloader, I hate it when my hulls have that nose-cone shape. I have no proof, but I think patterns will be better when the shot charge has a smother, unrestricted ride into the bores".
I other words I am leaving my Manufrance Idéal as is and shall continue to shoot 67 mm CIP shells from it galore.
And thank you for making me re-read the article and mend my ways.
JC(Alway Learning)
