0.604 inches http://www.wildfowlmag.com/tips_strategies/shotgun_062304/
.020
You can pretty much bet on full or modified, but the actual determination of choke is made by comparison the inside diameter of the muzzle to the inside diameter of the barrel before the bore. sales@countrygunsmith.net
The diameter of a 20 gauge full choke barrel typically measures around 0.615 inches (15.7 mm) at the muzzle. However, the exact diameter can vary slightly based on the manufacturer and specific design of the shotgun. Full choke constricts the bore more than other chokes, resulting in a tighter shot pattern.
bore diameter
The measure related to the diameter of the bore and the size of the shotgun shell is known as "gauge." The gauge is determined by the number of lead balls of the bore diameter that equal one pound; for example, a 12-gauge shotgun has a bore diameter that allows for 12 lead balls of that diameter to weigh one pound. The smaller the gauge number, the larger the bore size. This system is commonly used to classify shotguns and their corresponding ammunition.
To determine the choke of your Springfield Model 67 Series B .410 shotgun, you can start by examining the barrel for any markings that indicate the choke type, such as "full," "modified," or "improved cylinder." If there are no markings, you can use a choke gauge or a choke bore gauge specifically designed for shotguns. Alternatively, you can measure the diameter of the barrel at the muzzle and compare it to standard choke constrictions. If you're still unsure, consult a gunsmith or refer to the owner's manual for more detailed information.
'*' designates full choke (F). '*-' designates improved modified choke (IM). '**' designates modified choke (M). '**-' designates improved cylinder choke (IC). '**$' designates skeet (SK). '***' designates cylinder bore (CYL).
'*' designates full choke (F). '*-' designates improved modified choke (IM). '**' designates modified choke (M). '**-' designates improved cylinder choke (IC). '**$' designates skeet (SK). '***' designates cylinder bore (CYL).
25-100 usd
'*' designates full choke (F). '*-' designates improved modified choke (IM). '**' designates modified choke (M). '**-' designates improved cylinder choke (IC). '**$' designates skeet (SK). '***' designates cylinder bore (CYL).
'*' designates full choke (F). '*-' designates improved modified choke (IM). '**' designates modified choke (M). '**-' designates improved cylinder choke (IC). '**$' designates skeet (SK). '***' designates cylinder bore (CYL).
Generally the nominal diameter of cylinder bore is kept little smaller at cylinder head than at the bottom. The engine head will be generally heat and it tends to expand for these high temperatures. To prevent the bore diameter at head to exceed diameter at bottom,piston engine bore is ground with a slight choke.