There are some breeding methods that a game fowl breeder can choose in his breeding program like the in-breeding, line-breeding, cross-breeding, and out-crossing. These breeding methods are being used by fighting cocks breeder in order to produced superior battle cock that can win in any big time derby like world slasher cup, candelaria, bakbakan, rambulan, digma-an and other major derbies. But for me, I like to breed and fight them pure. For example, pure kelso, pure claret, pure butcher, and pure round heads are being fight in the derby without cross-breeding them to any bloodline. The reason why I like purebred because, by being pure, I believe that they are superior to others.
To produce a pure breed of game fowl or fighting cocks, you need a pure brood cock and brood hen, for example their bloodline is both butcher. Breed them together to produce a pure butcher bloodline offspring. Select the best offspring according to your purpose, for example if you want to let them fight in the derby select the best and condition or train them properly in preparation for the battle. If your purpose is to preserve the bloodline then keep them for breeding purpose.
You can use the in-breeding method and line-breeding method to produce pure breed. In-breeding means mating of full-brother to his full-sister or vice-versa. Line breeding means mating of brood cock to his pullets or mating of brood hens to her stags. You can also maintain or preserve the bloodline or families of your game fowl by mating the offspring of the full sister and full brother (cousin). In that way, you can produced a pure breed of fighting cocks that can be used as battle cocks or breeding materials.