Gages For Cylinder Throats?

[alamogunr]

A couple of issues back, Brian Pearce had an article in Handloader on cast boolets for revolvers. One of the pictures illustrated the use of what I would call a plug gage to measure the throats of the cylinder. I have always used an adjustable ball end gage and a micrometer to measure throats. How do these "plug" gages work? Are they tapered with a mark at the point that they measure the marked dimension, or cylindrical and work sort of like a go or no-go gage? Is my method sufficient? Should I at least have some method of checking my method for accuracy?

I looked in the MSC catalog and found gages but no description of how they worked. I'm sure most who use that catalog know what they want. There were many sizes and with a reasonable tolerance, they weren't overly expensive if you didn't need a bucketful of them. Any help would be appreciated.

John

[BD]

I use pin guages from MSC. These are just cylinders machined to a specific diameter, and they're not very expensive.
You drop the relevant size into the chamber from the rear and measure how how far in it will go. This tells you how deep the chamber is bored. A smaller one tells you at what point the throat taper hits that diameter. In a "good" cylinder all of the throats will be about the same. The guage which will pass all the way through should be within .001 of being the same in all of the chambers. IMHO three pin guages, (one throat exit diameter, one mid throat taper diameter, one just under chamber diameter) and a range rod will tell the story on a revolver pretty accurately.
BD

[fourarmed]

I have a set that goes from .250" to .500" by thousandths. I got them from ENCO. They have two sets. Mine has tolerance of +0 to -.0002 I believe. They also have one with zero to plus something. I figure if one of mine will pass through a clean, dry chamber mouth, it is within a few tenths of the pin diameter. Faster than an expandable. The set cost about $60 plus shipping. If you do much revolver work, they are very nice to have.

[alamogunr]

I have a set that goes from .250" to .500" by thousandths. I got them from ENCO. They have two sets. Mine has tolerance of +0 to -.0002 I believe. They also have one with zero to plus something. I figure if one of mine will pass through a clean, dry chamber mouth, it is within a few tenths of the pin diameter. Faster than an expandable. The set cost about $60 plus shipping. If you do much revolver work, they are very nice to have.

Is this the one?

Enco
.251 - .500 - .0002 ECONOMY PLUG GAGE SET
Type: Minus
Class: ZZ
Minimum Measuring Range (Decimal Inch): .2510"
Maximum Measuring Range (Decimal Inch): .5000"
Tolerance: +.0000",-.0002"
Number of Pieces: 250

Model #616-8131
Low Price: $62.68 ea $59.49 ea

[454PB]

I always use a lead slug to check chamber throats in my revolvers, but I find it interesting that I arrive at the same measurement by using a vernier caliper. It requires applying a steady pressure on the thumb wheel and turning the jaws within the throat as it is being measured, but is amazingly accurate.

[targetshootr]

I have Manson reamers for 44 and 45 cal which you can get with pilots that are round cylinders about 1/2" long in various widths. Might be what Pearce was referring to since I'm sure he has reamers. Handloader is my favorite magazine.

[fourarmed]

Alamo, that is the very set.

[Aldeer]

Elsewhere Pearce wrote that he used a plug gauge set from Grizzly Industrial. I got a set from them, about $65 if I remember correctly.

[Buckshot]

.............Pin gages are pretty neat to use. If the hole to be measured is only a couple tenths larger, the pin gage can be a real snug fit. Also the hole to be measured may NOT be really round. With the pin gage in place, hold the cylinder (or whatever) up to a bright light and try to see if there is any light passing the gage at any point. Many holes bear a striking resemblance to a 4 leaf clover :-)

For more exact measurements, nothing beats a soft lead slug driven through the hole (it will show only the smallest ID) and then miked. Use a light touch on the mike as the lead is soft and the curved surface the anvils contact is (in geometric theory) only a molecule wide. Lets just say, it's easy to put a slight flat on it.

................Buckshot

[GLL]

John:

Take a look at on-line industrial auctions. I picked up this nice Meyer "minus" set for under $25 because someone had spilled marking dye on a couple of the pins. It washed right off with acetone ! :)

If you only need a few, Meyer sells inndividual replacement pin gauges.

Jerry

http://www.fototime.com/6B38557F6AEEE8D/standard.jpg

[alamogunr]

John:

Take a look at on-line industrial auctions. I picked up this nice Meyer "minus" set for under $25 because someone had spilled marking dye on a couple of the pins. It washed right off with acetone ! :)

If you only need a few, Meyer sells inndividual replacement pin gauges.

Jerry

http://www.fototime.com/6B38557F6AEEE8D/standard.jpg

I've been looking the last hour or so. What would be the disadvantage of a "plus" set?

[uscra112]

I've used "pin" or "plug" gages for many years, but I've never seen the need for a complete set. Like my drill sets - only a few ever get used, and the rest just sit there.

You can buy individual pins from MSC or www.jlindustrial.com. Buy one that is exactly on the nominal dimension, one a tenth or two big, and one a tenth or two small. Just those three should be enough to let you determine what your throats actually are. If they want honing out, the small gage will tell you when you're close, and the nominal gage will tell you when you're there. I can recall a helicopter landing gear leg we made in the shop I worked at years ago, which had a very tight tolerance for a particular bore (not big - about 1" diameter") We couldn't get the machines to bore it or ream it well enough, so I took to reaming it about a thou undersize, then honing it out with a brake-cylinder hone. Using a series of pin gages to check my progress, I could nail the dimension to within .0001" every time.

In the auto plants where I do a lot of my work, they still use pin gages quite a lot. They always have them set in handles, but that isn't necessary - it's just convenient. They'll have a "go" gage in one end of the handle, and a "no-go" in the opposite end.