I will tell you that nothing works better than a shot snake for hunting with a smoothbore. That being said, and having made several in the past, there are things you must know for the project to be a success. The leather used must be strong but not overly thick, it must also be flexible or it will fail right where the valve fits into the neck of the snake. But, if it’s too stretchy, it will soon either fail, or become so long it isn’t useful. The snake should not have a large capacity ( it will wear you down, and cause the snake to ultimately fail). The irish valve measures the truest, but there is always the threat of losing the measure ( I put a lanyard on mine). Also the seam on the snake must be welted, glued, and preferable saddle stitched, to deal with the weight of the shot bearing on it all the time. Good luck.
Hungry Horse