This paper proposes a combined method of GCR Block Ack and Unsolicited Retry, which are standardized as IEEE 802.11aa GCR for audiovisual transmission, for lossless groupcast of binary data transmission over wireless LANs. Under bad wireless link conditions, the sender transmits each frame twice without acknowledgment as Unsolicited Retry. After the twice transmission, the sender enters the Block Ack sequence. To evaluate the effectiveness, we perform a computer simulation. We consider binary data transmission of about 40 MB and evaluate the wholly received time at all the receivers. The result shows that the proposed method can shorten the received time against the conventional Block Ack method.