I assume that you are talking about replica cap & ball pistols being converted to fire metallic cartridges. I hear good things about Uberti and Ruger cap & ball pistols. Most of these just require replacing the cylinder and having the fitting done by a gunsmith. If you want a more extravagant conversion you can have a loading gate installed and ejector rod installed in your replica. Make sure to always use a steel frame replica (no brass frames) and follow the cylinder manufacturers recommendations for the loads. Most of these cylinders are rated for blackpowder or black powder equivalent cartridges. You can also purchase these replicas with the conversion completed. Here are a couple of links that might help you.
Oh ok, No problem.
I strongly suggest that you do not attempt to convert any "blank firing gun" to fire actual ammunition of any kind. Any attempt to do so is extremely unsafe and has the potential to cause great bodily harm or death the shooter and by standards. These "blank firing" guns are designed to fire blank ammunition alone. These "blank firing" guns lack the structural integrity needed to contain the pressures associated with real ammunition. These replica blank guns are made of low strength alloy metals and other light weight materials. The chamber and barrel pressures alone would be more than enough to cause one of these blank guns explode! Not only that, but the frames, slides, springs and other parts would not be able to withstand the recoil and other forces created by firing actual ammunition. A project like this would most certainly end up being hazardous to you health. I hope this answered your question. Have a great day!!
There are no blank firing guns made to handle the pressure created by firing real ammo and modifying one to do so is dangerous. Just because some one did it, does not mean it was safe to do. I do NOT recommend trying to convert any blank gun. There are many grades of steel and the barrels on blank guns are not made with a high quality product. You can injure yourself and any bystanders. Buy a gun made to shoot modern ammo if you want to shoot modern ammo.