Long Shells in Short Chambers, Sherman Bell with technical assistance from Tom Armbrust in Finding Out for Myself Part V, Double Gun Journal, Winter 2001

The test barrel was a heavy Krieger barrel with piezo-electric transducer at 1 from the breech and an Oehler velocity gauge 2 5/16 from the breech.
Tests were performed:
1. 2 1/2 chamber with a 7/16 forcing cone British chamber (BC)
2. 2 1/2 chamber with a 1 1/4 forcing cone Modified British chamber (MBC)
3. 2 3/4 chamber with a 1 forcing cone American Chamber (AC)
Each load was tested in each chamber at least 5 times.
No significant change in velocity was noted between the 3 test chambers

Scroll down about 1/4 here for details
https://docs.google.com/document/d/1ZIo0y746UsSRZIgRuuxwAbZjSBHitO_EanvwLYc-kGA/edit

And with due respect to Bros. Bernoulli and Venturi wink
Shotguns: big tube/low pressure
Rifle: little tube/high pressure

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