Broke-disc Mountain

James, Nathan, and I got together and did an experiment with penetration. Wait. Let me try that again. We all got our guns together and saw how much of a brake disc (from a late 90s Tercel I believe) they could get through. James took the pictures, so they're good this time. All rounds were fired from about 25 yards out. Family picture below:

Long guns (from left--BOLD= James', plain italics=mine): DPMS Sportical, FN TPS, Benelli Nova, AXR, Mosin-Nagant 91/30, LWRC M6A2 (center--belongs to Nathan)
Handguns: M&P 9, Steyr M9A1, Beretta U22, TTC (center)

First up was the TTC pistol, firing a 7.62x25mm full metal jacket, which weighs in at 86 grains and moves at between 1390 and 1500fps (Most manufacturers claim 1390fps, while some UNCONFIRMED posts on the interwebs have the velocity at an ear-splitting 1500fps). Results below:
You can see that it penetrated the first layer of steel, and shattered on the second layer. That's pretty impressive for a handgun. A 9x19mm will only shatter on the first surface (we tried). The 7.62x25mm round has a higher muzzle velocity and a smaller cross-section, so it follows that it would penetrate better than most other pistol cartridges.

Next up was Nathan's (VERY nice) LWRC M6A2 chambered in 6.8mm SPC (a.k.a. 6.8mm Remington). He fired a volley of three and hit the hub area, which is only one layer thick. Of course it went through like a hot knife through marshmallows. Then James shot with his AXR chambered for 5.56x45mm, and I followed up with my beloved Mosin-Nagant 91/30 chambered in the ancient 7.62x54R. The AXR had some trouble penetrating the tougher bits of the disc, but performed admirably. The 91/30 didn't realize there was a brake disc hanging on the fence post, and continued on. If you own a house on the opposite side of the planet, there may be a 7.62x54R bullet hole through it, as I believe that round may be able to penetrate the entire Earth. Labeled picture below:
A third whack with the MN 91/30 resulted in the brake disc splitting in two. Here I am holding it, and trying to look super badass.

No, my arms aren't 18" long and my head isn't quite that large. It was a funny angle. I'm sticking with that story.

I think one lesson we can learn is to NEVER count C&R guns out, as the two senior citizens of the group performed very well. Second, the 5.56mm round displayed some irregularities, as two rounds appeared to have been at least partially deflected (they impacted at a very shallow angle), while several others shredded the meatier section of the disc. I think angle of attack has a lot to do with the 5.56's ability to penetrate hard surfaces. The 6.8SPC probably relies on its greater mass and sectional density to hack through the metal. I wish Nathan would have put a round through the rim (which is twice as thick) and see how it fared. The 91/30 proved once again that bigger+faster=better. That said, if I had to carry a weapon all day long, I'd prefer the AXR or M6A2 for their lighter weight, and not being as long as a bus. Of course, the 91/30 remains a very useful and tremendously powerful rifle.

All in all, our experimentation with penetration was a great deal of fun, and I hope we do it again some time. After all, it is legal in Iowa.