Hi, this is one of the first 3rd generation Colt SAA. The two extra cylinders are one in .45 Colt with cylinder bushing and the other is a .45 ACP cylinder that I fitted to this revolver. The original early 3rd generation .45 Colt cylinders used a pressed in base pin cylinder bushing.
This is one of my most favorite revolvers. There are a lot of 1873 clones, but you've got to love the pony.
Regards,
Richard