In recent years, much work has been done on attempting to scale multicast data transmissions to hundreds or thousands of receivers. In today's Grid environments, however, a typical application might involve bulk data transfer to just ten or twenty sites. Using multicast for this type of application can provide significant benefits including reduced load on the transmitter, an overall reduction in network traffic, and consequently shorter data transfer times. In this project, we are investigating how multicast can be exploited within such an environment without requiring major changes to applications or underlying networks. The approach taken is to modify TCP to support multicast transfers, and run this modified TCP engine over UDP as a userspace transport protocol. We describe the work to date on the design and implementation, and provide some early experimental results.