Is the evidence I found enough to get a change in custody?

If I understand your question correctly, your ex has physical custody of your child ( presumably pursuant to a court order) and you went through your ex's cell phone and found text message material that you copied / took pictures of and now you want to file an application with the court seeking a change in the custody plan to give you primary physical custody of your child and the "change" is that you now have information suggesting that your ex is in possession of illegal drugs and illegal or illegally obtained weapons.  For the moment, let’s put aside how you obtained this information and let’s put aside what a judge would do with this information if presented to him, what has changed in your life to warrant a change in physical custody of the child? A prior order or agreement gave him physical custody of your child. Either you and your ex agreed at the time that it was best for your child or a court found that it was best for your child that he has physical custody and now you want that changed - what has changed in your life to support the conclusion that you would now be the better primary custodial parent? Simply saying that he is doing something illegal does not mean that you automatically win or are deemed the better parent. My suggestion is that you sit down with an experienced family law attorney and review the prior court order / agreement and your new information to discuss your options.