Not sure how long this will last, but right now you can download Gunsmithing by Roy E. Dunlap free for Amazon Kindle (can also download the Kindle app on your phone or PC).
http://www.amazon.com/Gunsmithing-Stackpole-Classic-Books-ebook/dp/B004BDORIS/
http://www.amazon.com/Gunsmithing-Stackpole-Classic-Books-ebook/dp/B004BDORIS/