158gr JSP Expansion

158gr JSP Expansion
July 22, 2020 Sierra Bullets

158gr JSP Expansion

By Philip Mahin

Well, this is the last expansion test I’ll be doing using the 357 Magnum, but it has been an interesting adventure. My earlier test using our 158gr JHC gave a result that I thought was ideally suited for the 357 Magnum cartridge in a revolver. You can review that HERE for yourself if you wish. What I thought would be a close comparison turned out to be a whale of a difference in this bullet compared to our JHC. Let me explain. Our #8340 158gr JSP Sports Master bullet turned out to be a lot tougher than I thought it should have been and I wouldn’t hesitate to use this one through a bone structure if I needed to. The impact velocity was at 1,400fps, from a maximum charge in my revolver. It was found in the 9th jug, so it gave +48” of penetration through my test medium. The nose profile bulged a little and it weighs 149.52 grains, so it did loose a little of the lead nose somewhere.

I couldn’t push it any faster because of pressure signs but a rifle using a longer barrel could give a faster velocity from less pressure. From a rifle, the 357 Magnum has the possibility of pushing it to 1,800fps and from a trajectory perspective, that means it will slow down to a 1,550fps impact velocity at 50 yards. An awful lot of whitetail have been taken within that distance so I wouldn’t hesitate to use it for such. In my mind, this bullet was made for rifle velocities and I hope to be able to test my theory someday. If you will, possibly consider this for younger shooters as a good way for them to enter the world of fair game hunting as it could produce very little recoil. When I say very little recoil, I mean just slightly more than a 223Rem cartridge shooting our 65gr SBT GameKing if the firearms weigh the same. That would be pleasant shooting even for me.

The guys in the R&D department here heard of my project and offered their expertise. They had an expansion test using this bullet into calibrated ballistics gel and the results were just as I would have expected. From a rifle offering a muzzle velocity at 1,860fps and having an impact distance of 50yds, the impact velocity should be just shy of 1,600fps. This bullet shown here has an average expansion of 0.740” and weighs 149.1 grains. It also gave 14.25” of penetration, but a secondary test at a 70fps slower impact gave 2.5” more penetration with a very similar bullet performance. That is the equivalent of taking a 75yd shot instead and I wouldn’t hesitate to use this in my personal hunts.

I want to give a shout out to Mark and Tommy for all their help with my update, I truly appreciate their efforts. Remember to be kind to one another. In a world full of craziness, a simple word or act of kindness can go a long way. Who knows, your one simple act may be as contagious as a plague. Till next time, have fun shooting and be safe.

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