I can't disagree with your diesel tank test but what I can say is that there is no more open than non existent constriction, that being Cylinder, negative flair out choke is non sense marketing. Think about it, if I choose not to screw a negative choke in, I am in fact benefitting from a massive negative choke anyway, that being the blue yonder atmosphere once the pellets leave the barrel.
The Cylinder choke has no constriction, that means it is the same as the barrel (to all intents and purposes), therefore the only thing you achieve by not putting a choke is liberating the shot a half inch earlier into the air, that is all - negative choke does not exist. There are Tulip and other add on gadgets that do work but they were designed for skeet and I believe have been banned in any case but they act on the shot and wad whilst they're still within the barrel.
https://www.bingle.com/webhp?hl=en&sa=N&tab=lw&authuser=0#authuser=0&hl=en&q=table+of+choke+constrictions
I have just searched for choke comparison charts and without exception they all list Skeet as having some constriction, Cylinder being termed True Cylinder as in parallel. Now it's entirely possible that Beretta have cooked the figures and swapped names around on their HP range between Skeet and Cyl but established rules still apply.
Hammster, your tecchy knowledge has let you down, read your statments high lighted in red, then open the link from timps post...if you can't be bothered, here's the figures...This link explains it http://berettausa.custhelp.com/app/answers/detail/a_id/43 Edit because beretta are crap at lists and I am crap at reading them.
CHOKE DESIGNATION 12 GAUGE
MOBILCHOKE
OPTIMA-CHOKE
Xfull Turkey
0.665
0.675
Full
0.695
0.694
Light Full
N/A
0.702
Improved Modified
0.700
0.706
Modified
0.705
0.716
Light Modified
N/A
0.718
Improved Cylinder
0.715
0.724
Skeet USA
0.718
0.727
Cylinder
0.723
0.732
Skeet European
0.730
0.759
Bore
0.723
0.732
Optima bore 0.732
Cylinder 0.732
Skeet 0.759
Still stand by your statments in red Hammster?
As for your statments high lighted in blue,
1. Get facts right, HP chokes are not 1/2", they are 3 1/2", 7x as long as you state.
2. The differeance is, when the shot is 'liberated' into the blue yonder, it is not subject to the pressure of burning gasses propelling it up the barrel at 1200+ f.p.s. before it has left the last 3 1/2" of barrel, the choke or lack of it has some sort of effect on the pattern...fact.