Calipers and Tools In General

[Fotheringill]

I know I am preaching to the choir, but just some thoughts on possibilities.

I was getting various measurements on final OD after loading a bullet with my micrometer.

With calipers, it was more or less =/- .05 thousandths.

For whatever reason, I then used my calipers the get an ID on the Redding bushings I use. They seem to be consistently measuring about .002 narrower than what was marked on the dies.

My first thought was that it was me.
Second thought was that Redding mismarked the bushing dies.
Third thought was that the ID measurement with the calipers was inaccurate.
A shooting pal (machinist) offered to bring the calipers to work to do accurate testing on both the OD and ID features of the calipers.

These were cheap General 6" steel calipers.
Good news- OD was spot on.
Bad news- ID was short by 2 1/2 thousandths.

Previously, I had only used the OD feature to measure base to ogive, without any problems.

Moral of the story- buy better tools for accurate readings.
Lesson Learned.

 

[AJC]

And knockoff tools are huge.

 

[powderbrake]

You can not accurately measure small hole ID's with a caliper because the touch of the inside measuring tips do not exactly lie on the centerline. You should use a Small Hole Gage and an OD micrometer. It takes a bit of "feel" to get good readings, but it should be OK on the ID of a neck bushing.

I would use a micrometer on the loaded OD.

I have never measured the ID of my bushings, I have assumed they are correct. I may be wrong, but as part of setting the neck tension, I let the target tell me the answers.

Pic of small hole gage from Ebay



Mitutoyo makes good instruments that are not as expensive as Starrett. A good digital caliper and a good 1" OD Micrometer are good investments. I am still using the Starrett 1" mic I bought when I started my first engineering job in 1960.

The small hole gages can be cheaper, unless you need to use them a lot.

I use a Mitotoyo 500-171-20, the current version is 500-196-30. here is a link to one on amazon. https://www.amazon.com/dp/B00WMKUUAQ/?tag=accuratescom-20

Here is a 1" mitotoyo micrometer https://www.amazon.com/dp/B00WMLEA6K/?tag=accuratescom-20

They may be at a different price level elsewhere but this is to show a very good quality tool that will last a lifetime.