Maybe my experience can help shed a little light on this subject. Several years back I purchased a used, 15" .357 Maximum barrel for my Encore stamped "Coyote Guns". I started working up loads for it, and once I got to moderate loads, the action would open when I fired. The first time it happened I knew that something funny had occurred. I didn't move, just took in the details of what everything looked like. It looked normal - action was closed, resting on my shooting bags, right hand still wrapped around the grip. But I KNEW something funky had happened. I looked down at my lap and, lo and behold, there was a fired .357 Maximum case lying in my lap! I thought, "What the hell?!?!?" Then I opened my gun. Sure enough, chamber was empty. What had happened is the frame opened when I fired, the snap of the action opening ejected the case, then snapped back shut. Of course I quit shooting and went to the shop to figure out what the hell had happened. I got out my feeler gauges and measured headspace. IIRC, headspace on that barrel was .014". Light was easily visible between the breech face and the barrel face. I got online and started doing some research. I knew from previous experience that the headspace varies from barrel to barrel based on the placement of the lug and hinge pin hole. I also found out that Coyote Guns was no longer in business, partly because his Encore barrels had excessive headspace issues due to misplacement of the barrel lug, which affects how far the locking lugs enter into the locking lug recess in the frame. I tried various solutions to keep the frame closed on firing and finally succeeded by carefully stoning the locking lugs so they were square on the end and had more purchase on the recess area and I installed a muzzle break to reduce the recoil and stress on the frame. If my barrel would have been a .300 Win Mag, with the recoil and pressures involved, combined with the much larger case head on the breech face, I can completely see exactly what happened to Brian. The frame, due to excess headspace, came open upon firing because the locking lugs did not fully engage in the locking lug recess. The recoil, being restricted by his shoulder, had enough leverage due to the long barrel and recoil force that the stock snapped in the grip when it came open, and then snapped back shut. All of this happened in a split second. I would bet a large sum of money that the fired case could be found somewhere within 30 feet of where he fired, straight behind him.
Brian - I'm sorry for your experience and the loss of your sight. Headspace issues have been known with these guns for years. Mike Bellm dedicates an entire page on his website and a specific tool for measuring headspace and setting resizing dies for the TC Contenders and Encores. But Mike's stuff is for OCD reloaders like me and intended to solve fail-to-fire issues and extend brass life - not to resolve inherent safety issues if the barrels have excess headspace.
Even on a break action gun, you cannot evaluate headspace with a feeler gauge. That will only tell you if a gun is on face, it tells you nothing about the condition of the chamber. You could have a barrel that is perfectly on face wit a chamber cut WAY too deep, and thus headpace is excessive.
