380 sizing question

  • Last Post 04 May 2017
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zhughes posted this 03 May 2017

Hi all, have a question around diameters. I have a 9mm that slugs at .355. My 380 slugs at what appears to be .354, which seems odd, but ok.

Question is, would it be safe to shoot .357 cast in a barrel that tight? What's driving the question is I have only cast for 9mm and want to start casting for 380ACP. I've been loading unsized to date but would like to start sizing to help with bullet seating consistency... And I would love to only have to buy one sizer for both calibers.

Thanks! Zach

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onondaga posted this 03 May 2017


Make a 380 dummy load with the Un-sized bullet you have and test chamber the dummy. The answer is a helpful first test. If it won't chamber you can be sure it NEEDS to be sized. If it chambers, load some up for test firing.

Cast bullet fit is more relevant to chamber fit than to barrel slug measurements. The largest diameter bullet that will easily chamber is the best cast bullet fit regardless of the bore slug measurement.



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BigMan54 posted this 03 May 2017


I actually use the barrel assemblies, of my auto-loading handguns as  chamber checkers. If it fits, it shoots. But I do size 9mm at .356, seems to function & shoot best in my different 9mm handguns.  A happy medium.

Long time Caster/Reloader, Getting back into it after almost 10yrs. Life Member NRA 40+yrs, Life S.A.S.S. #375. Does this mean a description of me as a fumble-fingered knuckle-draggin' baboon. I also drool in my sleep. I firmly believe that true happiness is a warm gun. Did I mention how much I HATE auto-correct on this blasted tablet.

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zhughes posted this 04 May 2017

I read a couple other places online that you had to worry about size on the 380 because it was so small and pressure can build quick with oversized bullets. Could they have been referring to jacketed instead?

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Ed Harris posted this 04 May 2017

FWIW I size bullets to .357 in all of my .380 and 9mm pistols, except for those which need .358!

NEVER seen a 9mm or .380 with chamber throat so tight that it needed .356 other than a min. SAAMI pressure barrel.

NATO and CIP spec barrels as in all European pistols will be fine with .357.

I DO size .358 for my two Beretta M1934 .380s, both Ruger LCPs and my friends who load for several Beretta 92s all size theirs to .358.

I used to have a Browning GP Competition which needed .357 and my friend Dennis Carlini sizes .357 for his SIG P210 and I do also for two SIG P230s.

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

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zhughes posted this 04 May 2017

Thanks Ed. Glad to hear someone else with a success story on this topic.

Got the .357 sizer ordered!


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