The blown primer indicates very high pressure, which is to be expected. However, my intuition suggests that the column of water would be approximately the same as a plugged barrel and cause failure of the receiver or a split barrel. I am surprised that the pressure can evacuate the water faster than it can increase to cause catastrophic failure.

Some of these super slow motion videos show some interesting things. Notice the barrel flex (you can see the front sight depress and torque).

I've seen a video like this of a FAL firing and the barrel was moving all over the place. I wonder if the AR15 is as bad. Suppose it is strictly due to barrel thickness or weapon design?

quote:

Originally posted by A7Dave:
Some of these super slow motion videos show some interesting things. Notice the barrel flex (you can see the front sight depress and torque).

I've seen a video like this of a FAL firing and the barrel was moving all over the place. I wonder if the AR15 is as bad. Suppose it is strictly due to barrel thickness or weapon design?

I saw a video of a AK47 and M16 firing in slow motion. The barrel was flexing so bad on the Ak and the cleaning rod dancing around so much I wondered why it didn't fall out of the rifle. The bolt went back every which way but straight. The M16 did nothing but vibrate.

I noticed that on the underwater video too that the front sight jumped around and looked to me that the barrel dipped down at one time.

I have seen a lot of videos of weapons being fired underwater. The one warning that is always given is to make sure the barrel is totally filled with water. That prevents the extreme pressure spike.
The most interesting video that I saw was taken at a Soldier of Fortune convention in Las Vegas, I think in the early 80's. A demonstration of firing numerous weapons underwater was conducted in the hotel swimming pool....apparently to the dismay of hte hotel manager. They fired a number of different weapons in the pool.
None the less, this was an interesting video to watch since most videos are shot in a pool. It was interesting to see how the tank exploded rather than just breaking. Thanks for posting the link Saeed!