Major Mental Blank!! Need help!

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Potashminer

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There is (or at least, was) a set of ground rods, in diameter increments of perhaps .001" that one used to measure the diameter of a hole - specifically, a five grooved bore could be measured by trying for a slide fit of one of those rods, to come up with a "bore diameter". I seem to recall them in sets - like .250" to .500" or some such, but for the life of me I can not remember what those sets were referred to, nor is google any help! Anyone remember??
 
I believe I have Deltronic Pins... I'll go and look...

I'm back... yes mine are made by Deltronic and available in every 10 thousands of an inch. Accurate to +.000040"/-.000000".

I bought them out of Seattle for about $15 each...

I have them for .22, 6mm, 6.5mm, 7mm, .30.
 
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I have this set, .251 to .500.
It was pretty heavy and the outfit selling it wouldn't ship to Canada.
I had it sent to my brother who was living in New Jersey at the time.
This was twenty years back.
 
I have made up several "plug" guages from old gun barrels (because many of them are free machining). Basically a tube about 8 or 9 inches long that goes up in steps of .002" with a groove separating each step. Put them in the muzzle and mark where they stop then mike the diameter. Handy for muzzle loaders of unknown caliber and barrels with odd numbers of grooves

cheers mooncoon
 
OP, there is another method to measure bores that is very accurate if care is taken.

Those rods are only good for measuring just inside the muzzle.

Here's what I use. I have a couple of boxes of cast lead bullets in different diameters that I use for this purpose.

I place the tip of a lead bullet over the bore and tap it gently until about a half inch or so is down inside. Then carefully tap it out with a cleaning rod and use a good micrometer to measure the obverse of the bore, which is what the lead insert will be.

Simple, cheap.

When you've finished, the lead bullet can go back to the melting pile.

There are also taper gauges available. The military used them to measure muzzle wear.

I had a set of taper gauges when I was still working for a living but ended up giving them to a young machinist as a graduation present. Mine were made by Starrett but I believe there are decent Chinese knock offs as well as Mitutoyo etc.
 
I hear you, Bearhunter. Have tried the lead cast thing - actually a slug. Have tried Cerrosafe casting. However, it is the bore diameter I am looking for, not the groove diameter - actually to specify the size of the pilot for a reamer, so the area ahead of the existing chamber is where I am trying to measure bore diameter. Was thinking a slip fit pin gauge would be as close as I can get for bore diameter.
The rifle was discussed here 6 months ago, had a different owner then - a BSA Model "D" or "E" nominally in "270 Win", but appears to have a .270"-ish bore with .282" grooves. That groove size appears correct only for the defunct 276 Enfield, but who knows with British barrel makers? I am seriously considering reaming the chamber to 280 Rem, despite reservations from Canadian PTG rep, but would need a .270"-ish live pilot for a live pilot 280 Rem reamer, since the standard .275" pilot on the 280 Rem reamer on hand is too big to fit and I don't know any tool makers who can or would grind down that rigid pilot. PTG appears to list live pilots in .0002" increments. Either way, I need to come up with a dimension... My original post was because I simply could not remember what those "pin gauges" were called - easy enough to find on Internet now that I know what they are called.
 
For measuring just ahead of the chamber as you described is best done with a 'set' of pins that are in ten thousands of an inch, A pin set in 1 thou graduations is useless for this purpose.
 
Thanx for the clarification OP and GT.

I see where you're coming from now.

I'm lucky enough to be blessed with a "down inside gauge" Which I do use on occasion. At my last job, I was able to cherry pick the machine/tool shop for a lifetime supply of tooling for my lathes/milling machine and work shop. One of the gauges is a two legged affair mounted to a dial gauge. It has about a 6 inch reach down inside to measure small cylinder blocks/valve blocks etc. The biggest problem I have with it is that I have to pull the barrel to use it. Mind you about the only time I need it is if I'm going to be recutting an existing chamber.

Lots of different ways to do this but I can certainly see what you want to do and why.

Thanx again
 
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