Usually i have the hammer cocked back and i lock the bolt back to put it together. Glad you figured out your problem. Like i said make sure you check out a few videos on how to take apart that lower action assembly to put your buffer in, or you will have parts flying all over the place. I liked the video by Arrowdogger. He has a few video stickies on Rimfirecentral.com. In the Marlin forum.