Friday, May 15, 2009

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.


James said...

LWRC vs. LSRCNot sure that you remember, but the M855 rounds that were deflected were shot by me after Nathan hit the disc with his LWRC, and it was turned halfway perpendicular to us at that point.

That being said, the 6.8x43mm Remington SPC was pretty impressive for being the only fully lead-core round that we shot. I'm sure the AXR wouldn't have as much penetration if it were shooting M193 or .223. I would be sold on 6.8 if rounds weren't one dollar a piece. Breaking that disc cost Nathan three bucks!

Anonymous said...

The MN 91/30 had some ridiculous penetration of that brake disc. Glad to see your story had a happy ending, I was little worried at first...

DC Houghton, esq. said...

Corrections have been made.

I agree. The 6.8 shows promise, but it is absurdly expensive. Reloading brings it down to about the cost of loading .308win match rounds (with expensive IMR 4064 powder and Sierra MatchKing bullets). The 6.5mm Grendel looks more impressive on paper. It flies flatter for longer ranges, so I hear. We need to get Nathan to buy a Saber Defense AR in 6.5 Grendel.

James said...

Nah, 6.8 and 6.5 both use a 5.56 lower, right? Well, i know 6.8 does.

We need to get him to buy a cheap .223 upper and a .22 conversion, so he can actually afford to shoot with us.