Recoil Lug
Most of the dedicated BR actions have a squared off tang that will function quite well as the recoil lug if bedded properly. Have done several Panda's this way for silhouette shooters with great success. Just finished a Swindlehurst smallbore silhouette rifle and used the squared off tang on that for a recoil lug as well. On rimfires, a recoil lug is probably not an absolute requirement, but the Anschutz 54 worldbeater come from the factory with one. If you have a recoil lug available on a rimfire, it allows clearancing the screws in the pillars so there is no chance of binding and no worries of the action shifting in the bedding. On a rimfire it does pretty much insure that reassembly will be correct every time.