Good question. AFAIK Freedom Arms is the only one. Maybe its way easier to do in a revolver or bolt action rifle than auto that has a bolt (like a Ruger MkII or 10/22) .... shouldnt be but I don't know.Because rimfires going back to the civil war are more prone to misfires because of uneven primer compound in the rim why don't more firearms companies make dual firing pins in their products?