Venting is most definitely the best first method of safety, but the flange needs to be there as your last line of defense. No matter how well you think you've vented it out, your still gonna see some coming down the left raceway.

Matt's on target here.

This shroud received favorable comments from HP White Labs during destructive testing of the M1999. They said it was the best safety feature they've seen on a Model 70 type action in recent years. The M1999 is vented both sides, but that didn't save the "gas block" from becoming shrapnel. The gold color is deposited molten brass. Not stuff you'd want in your face.

Rod, any idea what they had to do to get a failure like that?

The usual way to deliberately get a failure is to load a cartridge with Bullseye under a heavy bullet.

Go to www.dsarms.com and watch the slow motion video of them destructive testing an FN-FAL.

Very high pressure gas has flow characteristics virtually identical to liquid. Also, the gas is expanding quite rapidly, so the more places it can go away from the shooters face the better. You don't think those big horse troughs in the bottom of the m98 bolts are there for esthetics do you? And that is just for a pierced primer.

I had an old .22 that finally gave up the ghost on me when I was 13-14. I was shooting cans back in the woods on our farm. I remember pulling the trigger and in the tiny fraction of a second that you see something but don't even have time to think about it, I saw the tiniest whitish cloud around the front of the bolt and then it felt like my father had slapped me across the face (he did too, once or twice). I dropped the rifle and felt my face, my eyeglass lenses had been collapsed into my sockets making my eyes reflexively clench tight. It took a few moments sitting in the dirt, crying, wondering if I'd ever see again. I made it back to the house where my mom spent some time cleaning the bits and pieces of black stuff out of my face with a needle.

That took quite awhile to get over. After a few hours me and my dad went back and looked the rifle over. The extractor was gone and there was a little crack at the base, just above the rim, that extended about 1/4 of the way 'round the case.

I believe this failure occurred around 110,000psi. Cartridge was 30-06, loaded by HP White in a pressure gun and then in the test model. The action was undamaged, and showed no set-back. But the gas block, extractor ring, extractor, magazine box, follower, follower spring, and floorplate were casualties of war. When the case head failed, the gas came out on the extractor cut in the C-ring of the breech. Broke the claw off, but did not dismount the extractor until the ring was flame cut. Much of the gas went into the magazine box. The follower, which is stainless steel about a quarter inch thick, was bowed like a banana. The box was ballooned and the flooplate looked like likewise bowed. The spring failed at the lower elbow.



This was on the very first machined prototype action, which had more exposed case head than the current production units. I would be interested in running this test again, with a few production actions from major players thrown in to make it interesting. And maybe some custom ones too. All it takes is money.

So what exactly does the handloader have to do to get such an overload?

Chuck

Rod, in this picture:
http://www.montanarifleman.com/images/screenshots/actions2_lg.jpg
It shows that the Montana M1999 uses a similar filler piece as the Winchester Classic M70 in the left raceway. Are you using this to regulate the rearward travel of the bolt only or is it considered to be a gas block? The parts diagrams on the Winchester website designate the part as a gas block. In your destructive testing of the M1999 how well did this part fair and in your estimation would it have done anything to help protect a shooter from an overload, casehead separation, or pierced primer condition? Thanks, Dennis