In my post above about rechambering, I forgot to mention one more key factor:
When a cylinder is faced off on the rear surface, it will obviously be shorter than it originally was. This fact means there is usually some "slop"- forward-aft motion of the cyl when the cylinder is open because it can move rearward an unusual amount before contacting the frame lug. The frame lug is the little "retainer" at the bottom rear corner of the frame window. This would be another indication that such conversions are not factory.

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Regards,
Lee Jarrett