Thats about 10 yards....I once heard it said that the pattern on cylinder spreads about an inch per yard...so at thirty yards its two and a half feet wide. Clearly full choke is much tighter. Shooting high pheasants, you might want 3/4 choke - but that would make a big mess of a close rabbit. I find 1/4 to a half is fine for general game - but avoid the really long shots. You might consider more for use in wildfowling for example.
BR I'm sure you know our chokes are rated differently over here. Do you know how they might compare? Ours are (from least choke to greatest) as follows:
- Cylinder Bore (no choke whatsoever and rarely ever used)
- Improved Cylinder (very little choke and usually used for close shots)
- Modified Choke (the standard choke on general purpose guns before the days of changable chokes and a good compromise for most shooting)
- Full Choke (once the greatest choke and used for long range shots such as dove, ducks geese, etc.)
- Extra Full Choke (a relatively recent choke size used for long range shooting with other than lead shot I believe)
- Rifled Chokes (intended exclusively for sabot rounds but occassinally used for rifled slugs as well) I know you don't have a practical use for slugs over there.
As asked; how do these correspond with your choke sizes?
Edit to add: The comment that modified was the standard choke before changable chokes is only partially true. It applied with single barrel guns. For doubles, usually the first barrel was modified and the second was full choke.