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Old 03-11-2017, 08:57 PM
sjs sjs is offline
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Default Plug Gauges

I want to buy hard cast bullets for my 629-6 and I want to measure the cylinder throats first. Other than an unsatisfactory attempt to slug the barrel of my .357 revolver, I have not done this kind of measurement before. I have plug gauges for .427,.428, .429, .430 and .431 in my shopping cart for MSC. They are all "plus" pins.

Does this sound like enough different pins to cover the possibilities?

Should I get the "minus" pins as well?
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Old 03-11-2017, 09:14 PM
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That should cover anything that is not wildly out of spec. Just the + ones will be fine if you want to measure in .001 increments. If you want to measure in (approximately) .0005 increments, get the - ones too.
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Old 03-11-2017, 09:16 PM
Walter Rego Walter Rego is offline
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The set of plug gauges that I use are Minus .0003". That means that a .430" marked gauge actually measures .4297". In other words you want minus gauges because you couldn't stick a .430" gauge in a .430" hole. Being minus by .0003" is close enough for measuring cylinder throats. If you can slide a .430" gauge in a throat but not a .431" gauge, the actual throat is somewhere between to .4297 and .4306" and you can use .430 diameter bullets.
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Old 03-11-2017, 10:18 PM
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I would add .432 and .433 as I have used both in measuring S&W cylinder throats.
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Old 03-11-2017, 10:46 PM
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Buy 0.427 through 0.433, minus tolerance. Buy the least expensive grade they have, which will be more than sufficient for what you are doing. Handling and using lab-grade pin gauges is beyond the capabilities and interests of most gun hobbyists. No sense in paying the extra money for them. Remember, with pins you are just doing a "go" check of the entire feature based on the Taylor Principle of gauging, not measuring, which is a different thing - necessarily a lot more complicated, and requiring more expensive tools.

The older 44 Magnums, Model 29s, and Model 629s sometimes have exit bores that are even a bit bigger than 0.433 by a few tenths, but it's not really important because I have yet to see one with chamber dimensions that allow >0.433" bullets with US commercial brass. Most older 44s won't allow bullets much bigger than 0.432 or 0.4325. I've never seen a newer gun smaller than 0.428.
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Old 03-12-2017, 03:20 AM
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I agree with M29since14. My S&W 44's range from .428" to .432" throats.

Just go with the "minus" (they're .0002" under marked size) plugs; they're cheaper if I recall correctly too. The pin gages also help you spot out-of round throats too (I got one of those I need to ream.).

A few years ago I was going to order just a "few" pin gages, like you, but finally decided to buy a (discount) whole set & I was GLAD I DID !!

I've used it so many times on my various guns it's was well worth the extra money. Great to check the barrel's bore for uniformity too, among others.

They make a great backdrop too.

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Old 03-12-2017, 05:53 AM
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Where are you buying your plug gauge sets? Cost?
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Old 03-12-2017, 09:54 AM
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Here are a couple of examples from eBay.
SHARS 190pcs BRAND NEW M1 .061-.250 STEEL PIN GAGE SET MINUS (-0.0002") | eBay

SHARS 190pcs BRAND NEW M1 .061-.250 STEEL PIN GAGE SET MINUS (-0.0002") | eBay
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Old 03-12-2017, 10:26 AM
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An unsized soft lead slug or round ball drove through a disassembled cylinder is easy to measure. Set cylinder on hardwood block and use a flat face brass punch. Just like slugging a barrel and no rifling to worry about on cylinder.
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Old 03-12-2017, 06:03 PM
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Thanks much for the great info guys.
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