Our subscription program is a little different then most people are use to. You add the AMOUNT you want to spend each month and that buys a certain number of ROUNDS for each caliber and grade combination. We currently allow a $1 increment for your subscriptions so you can match the amount you want to pay with the current price of the caliber. Keep in mind that prices do change and you will want to add a buffer to adjust for this.
Here's an example: You want to buy a box rifle ammo in a particular caliber every month. Today that ammo sells for $0.48 per round which is $9.60 per box of 20 rounds. In order to get one full box in your inventory each month you'll need to set your subscription for this particular caliber to $10. This will buy 20.8 rounds. Now if the prices change to $0.51 per round you're $10 will only buy 19.6 rounds which leaves you 0.4 rounds short of a full box. (Now if this is over a two month period you'll have 40.4 rounds which is two full boxes).