You might want to consider a charge like this one:
You are instructed that under the law of self-defense a person is justified in using force against another when and to the degree he reasonably believes the force is immediately necessary to protect himself against the other’s use or attempted use of unlawful force, [add as applicable] but not merely in response to verbal provocation alone, or if the defendant consented to the exact force used or attempted to be used by the other, or if the actor provoked the other’s use or attempted use of unlawful force. A person is justified in using deadly force against another when and to the degree he reasonably believes the force is immediately necessary to protect himself against the other’s use or attempted use of unlawful deadly force [or, to prevent the other’s imminent commission of ______________ (e.g., murder)].
“Reasonable belief” means a belief that would be held by an ordinary and prudent person in the same circumstances as the defendant.
“Unlawful” means criminal or tortuous or both and includes what would be criminal or tortuous but for a defense not amounting to justification or privilege.
Now, bearing in mind the foregoing definitions and instructions, if you believe from the evidence beyond a reasonable doubt that the defendant, in the county of Dallas and State of Texas, on or about the _____ day of ______, did then and there use deadly force in committing the offense of ________ as alleged in the indictment, but you further find from the evidence that, or have a reasonable doubt about whether, the defendant used force against _____________ only when and the degree the defendant reasonably believed the force was immediately necessary [either] to protect himself against the use or attempted use of unlawful deadly force by ________________, [or, to prevent the other’s imminent commission of ______________ (e.g., murder)], then you will find that the conduct of defendant was legally justified and will therefore acquit the defendant and say by your verdict “not guilty.” [and, if applicable] provided you recall that the use of force against another is not justified in response to verbal provocation alone [or, if the defendant consented to the exact force used or attempted to be used by the other] [or, if the actor provoked the other’s use or attempted use of unlawful force]. [Bold terms must be further defined or explained in the charge]
