The right bore is machined to 0.750in and the left bore 0.729in.
To avoid the cost of Bismuth cartridges, is it safe to use steel shot in either of these guns?
I have been told that if the bores are opened to half choke they will be suitable for steel. Is this correct?
As both your Kestrel and Zabala shotguns are modern nitro-proved guns, they are safe to use with Standard Steel shot loads, providing they are in good mechanical condition.
The maximum pellet size permitted in Standard Steel loads is 3.25mm or British No.3 shot.
This can be used through any choke.
Some cartridges are designated High Performance Steel and these must only be used in guns which have been specially proofed to a pressure of at least 1,320 bar.
The marks will include the words Steel Shot and there will be a fleur-de-lys mark as well.
BASC has a good advice sheet on steel shot on its website in the research section.