First thank you for your service.
Second - just be honest with her.
I'm lucky enough to have my own budget for firearms and ammo that is completely separate from the family budget (although sometimes I end up using my firearms budget to supplement the family budget when the wife wants to use money from the family budget for something like say a spur of the moment family camping trip - essentially my firearms budget is paying for that). That means that most of the time I am free to purchase firearms and ammo as I see fit that I can afford. Now I'm not a rich guy by any means and that means I'm NOT buying new guns every day, week, month or even every 6 months but when I do decide I can afford another gun (and NOT cut into ammunition for shooting) I can just go out and buy said gun without consulting the wife first.
I maintain this firearms and ammo budget by doing something else that I love as a side business. That pays for itself and makes enough of a profit that it can fund my shooting expenses.
In your case since you don't have that luxury you should just be up front and honest with the wife. I've found out, after a failed marriage and finally meeting my current wife who is my gift from God, that honesty and truthfulness is the ONLY way to go in a marriage. Granted sometimes you have to lie to your wife because you're trying to hide a present from her etc. Those lies though eventually come to light and since they were there to hide something she would ultimately enjoy they're not what I'd consider bad for the marriage. Basically don't start lying to her now. Trust me when I say I know from personal experience that something like that will just start you on a slippery slope.
This is who we are, what we do.