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Old January 13, 2013, 10:54 PM   #9
Senior Member
Join Date: November 8, 2007
Posts: 2,001
A different view:

I recently purchased a Ruger Flattop revolver in .45 Colt with an extra .45 ACP cylinder. When I received it, the cylinder throats would not accept anything larger than a 0.450" (-) plug gauge. After shooting about 100 rounds of cheap Federal .45 ACP loads with thick-plated "TMJ" bullets, the cylinder throats will all accept a 0.451' (-) plug gauge. I did not (yet)measure the constriction of the barrel at the section threaded into the frame, which is notorious for being somewhat constricted by compression during assembly, but I would expect that to have widened somewhat, too.

Before I start working-up loads for accuraccy, I intend to have the constriction removed and the cylinder throats enlarged to 0.001" more than whatever the groove diameter is without the constriction.

Granted, that is a revolver, rather than an auto-loader. But, I would expect that there is some related wear on auto-loaders that could affect accuracy. There certainly is with respect to function with light loads, so for light target loads, you would probably want to make sure that the gun is smoothed-out before deciding how low you want to go before reliability becomes an issue. Also, some auto-loadeers will throw the first round outside the group because it is fed by hand-racking the slide, rather than by auto-feeding, and the lock-up is different between those two operations. That can also smooth-out with use.

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