I have just signed up to imgur so if the above photo does not show 4 shot flasks blame them not me.
Thank you to everyone who helped with photos to help me with my question about how a Sykes patent shot flask operates.
I now know the answer as I stuck in a “cheeky bid”, £2 over bottom estimate at the last Holts sale and it won!
The one on the left is a modern repro , the middle 2 are Sykes patent, and the right hand one is unnamed and the odd one out.
The Sykes (and copy) have a shot measure with a slanted leading edge like a coal scoop.
When pushed into the flask, it slides under the bottom of the shutter forcing it upwards against the spring so that the shutter raises allowing shot to fill the measure.
When the thumb catch is depressed and the measure withdrawn the shutter descends to retain the rest of the shot in the flask.
The 2 genuine Sykes flasks are Adjustable 1 1/2, 1 3/4 and 2 oz.
That is achieved by an inner sleeve withdrawn by the button under the thumb catch, the inner sleeve is rotated slightly to disengage a stud from the 1 1/2 setting (much like an adjustable powder flask) withdrawn and reset to the quantity desired.
The odd one on the right is marked 1 1/2 and has no retaining shutter.
The measure has a squared off end with a slight scallop on one side.
Presumably the measure is withdrawn with the flask held upright, and the the lip of the flask held against the scallop to carefully decant enough shot .