I take it you refer to "disc set strikers" ?I dont think I have ever seen a Holland with them,at least not one made by them ,as to guns made for them may be a different matter . Gas vents went out of style when gas tight cases became the norm as they were no longer needed. I'm no sure weather Kensal is on the same track on this ,as a lot of top grade guns were made with disc set strikers . Although I have seen some of the repair type work he refers to . Done before the days of modern welding.