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Old July 17, 2018, 09:54 AM   #1
jonnefudge
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Powder coating and pressure?

From what understand a jacketed bullet increases pressures compared to a hard cast. How is it with the powder coating? Does it have the same effects on pressure as a copper jacket? Is ther any difference from a regular hard cast?

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Old July 17, 2018, 12:17 PM   #2
Beagle333
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From our experiences, we do believe it is more slippery than a lubed bullet and therefore has less pressure. Chrony results show about a 30 fps slower bullet when fired with the same load, vs the same lubed bullet. This would lead us to think that the pressure was lower because it took less to keep the bullet moving and it didn't build up and push the bullet quite as fast. This was in .357 magnums.
If you powdercoat some and push them through a size die with a hand press, you'll really feel what I mean, even when sizing down .003-.004", they really just slide through there easily.
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Old July 19, 2018, 03:10 PM   #3
reddog81
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Treat them the same as regular lead. The powder coat jacket is completely different than a copper jacket.
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Old July 20, 2018, 08:35 AM   #4
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The powder coat is a plastic resin. It may seem hard to you, but under pressure, it flows easily—more easily than a typical cast bullet alloy—having a lower modulus of elasticity and lower viscosity. It behaves somewhat like a thick grease, but better in that it doesn't come off and lose lubricity. It's like Teflon coating in an aluminum pan verses melted butter in plain aluminum pan in that sense.

The lower velocity Beagle333 mentioned is strong evidence the start pressure needed to extrude the coated bullet into the rifling throat is lower than a conventionally lubricated bullet exhibits. That allows the bullet to get further down the barrel before pressure peaks. As a result, the pressure is peaking in a larger volume than when there is no coating, which lowers the peak value (same amount of gas in a bigger space) and with it, the peak acceleration value experienced by the bullet and hence the velocity loss. Shooting moly-coated jacketed bullet in a rifle also reduces velocity and requires that you use a little more powder to reach a particular velocity.
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