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GM .54 Bore Size....................

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GM .54 Bore Size....................

Old 04-18-2007, 01:46 PM
Typical Buck
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Default GM .54 Bore Size....................

I talked to a ladytoday atGM about the.54 GM barrel measurements.She told me that the bore is between .540-.542" and the groove is between .560-.564".They recommend patches between .015-.018".Also a .535 ball for hunting.Do you have to double the patch dia. and add it to the ball size?Seems a little tight to me but I'm still learning.I have a .530 mold so I'm hoping it's not usless.A buddy gave me 50 or so .535 balls to try.I can't fathom getting a .020 patch down the pipe.Any ideas what to order or loads for this barrel.Our local gun store has squat for BP stuff so I'm mailorder only.............Got a wack of snow today so I'm not sure if it's worth going bear hunting today as planned? Thanx Harold
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Old 04-18-2007, 03:04 PM
Dominant Buck
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Default RE: GM .54 Bore Size....................

Remember when you figure the patch thickness you have to figure it twice since it wraps around both sides of the ball where it engages the barrel. So even with a .530 ball and .018 patch you have .530 + .018 + .018 = .566 which in a .560-.564 on the grove should still engage the rifling fine.
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Old 04-18-2007, 03:09 PM
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Default RE: GM .54 Bore Size....................

Just so you know, I have a .535 LEE mold that I casted two hundred roundball out of. They were so hard to load, I never made another batch. They did make dandy ammo for my wrist rocket sling shot thought. I use a .530 becauseI am not driving nothing down the barrel with a mallet. You should of seen my friend and I that day trying to load them .535 ball. We had to ram atree with the ramrod in order to seat the first one. The second one, I used a ball puller and removed. I bought the mold because some "expert" told me that was the size ball they shot. Try the ones you got. Loading these rifles should not be a major project.No I am not saying the person at GM is wrong, but try those .535 you got and then judge what is better.
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Old 04-18-2007, 03:53 PM
Typical Buck
Join Date: Jun 2006
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Default RE: GM .54 Bore Size....................

I favor using a 530 hornady RB and .017 pillow patch material in my 54 cal. barrel
I think I would start with the 530 dia: and go from there,I read a post that you have problems in buying pillow patch material from walmart in your location,I can if you like the next trip I make to walmart pickup 3 yards of the stuff and mail it to you if you like :
you can send me the funds later
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Old 04-18-2007, 05:28 PM
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Default RE: GM .54 Bore Size....................

It must also be remembered that you can't simply add the various measurements...patches compress to half their initial measured thickness when started into the bore
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