There are specific differences between 802.3at and 802.3af and they are not compatible. Here is a quick read:
http://blog.antaira.com/poe-802-3at-vs-802-3af/The R710 specifically requires: •802.3af power mode option allowing to leverage legacy PoE switches and to easily deploy
https://www.ruckuswireless.com/products/access-points/zoneflex-indoor/zoneflex-r710The ability for you to use the r710 on your 300 depends if it is capable of supplying 802.3af Please note the very last sentence.
Power over Ethernet: Cisco 300 Series Switches are available with up to 48 PoE ports of Fast Ethernet or Gigabit Ethernet connectivity. This capability simplifies advanced technology deployments such as IP telephony, wireless, and IP surveillance by allowing you to connect and power network endpoints over a single Ethernet cable. With no need to install separate power supplies for IP phones or wireless access points, you can take advantage of advanced communications technologies more quickly, and at a lower cost.
Some models support both IEEE 802.3af PoE and IEEE 802.3at PoE+ while others support IEEE 802.3af PoE onlyhttp://www.cisco.com/c/en/us/products/collateral/switches/small-business-smart-switches/data_sheet_c...