53 g in a month is good weight gain at that size. If your snake is eating every 4-5 days, it will grow well even if your prey items are a bit undersized. One other recommendation on weighing. Don't do it too often. There are a lot of micro-fluctuations in an overall macro-growth curve. As long as they are eating relatively regularly and nothing else is going on, I would say to wait at least a month between weighings (if not longer).