TK precision has moon clips for the GP100 that claim to headspace .40 correctly- could be an option

[2AinVA]

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[Bruno747]

Not quite sure how you head space a 40sw in a 10mm correctly with a moon clip. 10mm and 40 both head space on the case mouth. That would mean each round would have to have a stand with some sort of firing pin extension mechanism inside the cylinder behind the round to make up the difference between a cylinder cut for 40sw and one cut for 10mm.

Unlikely.

[Keiichi]

How the rounds headspace depends on the firearm and cartridge... As an example: my Glock 20 has reliably fired a couple thousand rounds of 10mm and several hundred rounds of .40 S&W. It's not possible for the .40 to headspace in the chamber, so they must be "headspacing" at the extractor (or in the pertinent case, moon clip) holding it in place for the striker (or hammer) to hit. This is also true for my MechTech upper for my G20 (100-ish rounds of Winchester white box .40 with no failures - besides coming out of the barrel subsonic and with a tendency to tumble).

If the moon clip held the .40 cartridge in position for the hammer to strike the primer, it would function without issue... the same way a .38 special functions in a .357 because it "headspaces" on the cartridge case lip.

[Ronin]

Not quite sure how you head space a 40sw in a 10mm correctly with a moon clip. 10mm and 40 both head space on the case mouth. That would mean each round would have to have a stand with some sort of firing pin extension mechanism inside the cylinder behind the round to make up the difference between a cylinder cut for 40sw and one cut for 10mm.

Unlikely.

There's enough of a variance between the rim thickness of .40 S&W vs 10mm rounds to create a gap that can lead to light strikes.  The solution is to use a thicker moon clip with the Ruger GP100 when shooting .40 S&W.  The ones from TK work as advertised, but they're expensive at $80 for 10.  Ranch Products makes moon clips for the S&W 646 that will also work for all varieties of the 10mm GP100s.  They only cost $9 for 10, so that's a significant savings.  And they work with both .40 and 10mm.

[2AinVA]

There's enough of a variance between the rim thickness of .40 S&W vs 10mm rounds to create a gap that can lead to light strikes.  The solution is to use a thicker moon clip with the Ruger GP100 when shooting .40 S&W.  The ones from TK work as advertised, but they're expensive at $80 for 10.  Ranch Products makes moon clips for the S&W 646 that will also work for all varieties of the 10mm GP100s.  They only cost $9 for 10, so that's a significant savings.  And they work with both .40 and 10mm.

Thanks for the link!


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[jamestap]

Not quite sure how you head space a 40sw in a 10mm correctly with a moon clip. 10mm and 40 both head space on the case mouth. That would mean each round would have to have a stand with some sort of firing pin extension mechanism inside the cylinder behind the round to make up the difference between a cylinder cut for 40sw and one cut for 10mm.

Unlikely.

There's enough of a variance between the rim thickness of .40 S&W vs 10mm rounds to create a gap that can lead to light strikes.  The solution is to use a thicker moon clip with the Ruger GP100 when shooting .40 S&W.  The ones from TK work as advertised, but they're expensive at $80 for 10.  Ranch Products makes moon clips for the S&W 646 that will also work for all varieties of the 10mm GP100s.  They only cost $9 for 10, so that's a significant savings.  And they work with both .40 and 10mm.

Damn, and I spent a fortune on those TK
custom, which requires their mooning tool cause they're tight as hell.

In reply to someone's question about how the .40s headspace: the thick moons essentially turn the .40 in to a rimmed round.

[RJM52]

I just bought a package also but since I already shoot revolvers in 9mm, .38 Super and .45 ACP I had the tools to both load and unload the clips....

They are of very high quality and don't think you will wear one out or damage it in "normal" use....

Gun runs slick with zero misfires....

The reason 10mms work with the factory clips is because the factory clip is not controlling the headspace, the ledge in the chamber is.  The only thing the clip is doing is facilitating ejection.  The clip is too thin to correctly hold the .40 for proper headspacing which is why there are so many misfires...

Bob