The pilot stated that his landing to runway 36L was firm but not hard enough to “break anything”. He did not perceive that there was any side loading. The pilot applied brakes and felt the airplane pull to the right, so he steered the airplane to the grass on the right. The pilot stated that the right main landing gear collapsed, and the right wing hit the ground. An onsite examination revealed that the airplane struck a runway sign as it departed the runway to the right. Three separate tracks, consistent with both main and the nose landing gear, extended from the side of the runway and terminated at the airplane. The airplane sustained substantial damage to the right wing. After the airplane was lifted the right main landing gear extended and the downlock was found to be broken. A postaccident examination of the downlock and right main landing gear revealed no anomalies that would have precluded normal operations. At the time of the landing wind was 300° at 7 knots with gusts to 19 knots.