Measuring Finished Chamber Dimensions

[LVLAaron]

confirm you do not have an oversized back end

phrasing

 

[Jud96]

Thank you guys for the information and input.

I do measure my reamers to record their actual dimensions, because I have had reamers I ordered and took for granted they were right but actually were .001-.0015 over.

I think I’m going to get a 3 point bore mic and some pin gauges in .0005 increments to check the base diameter on my finished chambers. I just want to make sure my setup is working, and I like to inspect all of my work for peace of mind.

 

[LVLAaron]

How are we accurately measuring a tapered bore?

 

[Jud96]

How are we accurately measuring a tapered bore?

That’s my main question. I don’t have much experience measuring bores with as much taper as a chamber, so that’s why I was curious what others were doing.

 

[DaveTooley]

This rabbit hole can get deep and expensive. SAAMI tolerance on say the Creedmoor case is +.002" on diameter. The .200" line is .4714". I would get three gage pins. One .4710", one .4725", and one .4735".
Make up stops to go them so you can set the depth. Example; Rem 700 with a counterbore, set the stop at .200"
Then if the .4735" goes in I want to listen to the call to the reamer maker.

You could ask for an inspection report on every reamer you buy. I have one that goes out into the millionths.

 

[Tim Singleton]

In Daves example if you have a a chamber that a .4735 to .474 gauge will go into the 200 line your setup maybe allowing some wobble

 

[DaveTooley]

How are we accurately measuring a tapered bore?

gage balls are the best way.
Or your very own CMM

 

[Alex Wheeler]

Your .2-1.2" inside mic is fine. Eyeball .050" into the chamber and that will give you close to the .2" diameter. If your less then .0005" over spec on the print your fine, as most reamers are at least .0003 fat. If you hold the reamer you know its good when you cant just pull it out without a twist.

 

[tobnpr]

Cast the chamber and measure it at whatever datums float your boat.
It's not complicated.

 

[Alan Warner]

gage balls are the best way.
Or your very own CMM

Dave,
If I was to invest in the styli for my renishaw for our cmm, each inspection would be at least 150.00 for a good while
For a rifle chamber, g age pins at known depth and math is close enough

 

[LVLAaron]

I like the “wiggle the reamer” method. If I’m going to measure I want exact datums and locations… otherwise the number is wrong. I know we can get “close enough” but if close enough is good enough so is wigging the reamer? Assuming the reamer is correct-enough.

 

[FireMedic]

That rigid reamer holder craze has lots of chambers running big!

 

[Sniperhandle]

The pusher is the most accurate way to get a tight chamber, Either use a Bald Eagle or make one like Dave Tooley's.

 

[liljoe]

I was watching a video from a very well known engine builder and he made the statement "If you can't measure it, you can't fix it".
Joe

 

[Tim Singleton]

Dave's method tightened me up!

 

[jackieschmidt]

I was watching a video from a very well known engine builder and he made the statement "If you can't measure it, you can't fix it".
Joe

True.
As a Machinist, I have to figure out ways to measure a lot of things. Sometimes laying on a 20’ scaffold on my back under a boat sitting on a drydock..

I measure both inside and outside tapers all the time. The difference is, they are quite large, with plenty of room to get exact points of measurement. Often the smaller things get, the more difficult it can become.

A lot of machine work, especially manual machine, requires a lot of common sense and figuring out things. That’s part of the Trade.

 

[Skedaddle Shooter]

This has been a very interesting thread with an experienced smiths and machinists contributing. I am at the beginning of the learning curve when it comes to running a lathe. My question as a beginner is: If you have measured the reamer and are confident it is sized within tolerance and it is a piloted reamer with a bushing that fits correctly, wouldn’t you just need to measure the diameter of the chamber at the .200 line with a gauge pin to detect if the reamer was inserted concentric with the bore in a stable setup? If the gauge pin hits the number at the called out dimension at the .200 line doesn’t that tell you the chamber was cut to size and not oversized as long as the pilot keeps the front of the reamer centered and snug?

 

[ELR LVR]

I rely on the barrel setup ( most important ) and pushing the reamer to minimize any influence on the reamer. Myself and many customers have moved brass from one barrel to another with minimal sizing, which confirms my methods.

^^^This
push the back of the reamer and allow it float to be able to constanty center itself with the bore
and stay centered without any outside influence to push it off center

 

[LVLAaron]

This has been a very interesting thread with an experienced smiths and machinists contributing. I am at the beginning of the learning curve when it comes to running a lathe. My question as a beginner is: If you have measured the reamer and are confident it is sized within tolerance and it is a piloted reamer with a bushing that fits correctly, wouldn’t you just need to measure the diameter of the chamber at the .200 line with a gauge pin to detect if the reamer was inserted concentric with the bore in a stable setup? If the gauge pin hits the number at the called out dimension at the .200 line doesn’t that tell you the chamber was cut to size and not oversized as long as the pilot keeps the front of the reamer centered and snug?

How do you accurately determine where the .200 line is? And how do you measure it?


To answer some of your questions with other data... Some chambers are oval. Some are octagon shaped. If they're oversized they're probably an odd shape. How would you measure those?

Just some food for thought.

 

[ELR LVR]

Thanks Jackie. My goal is to have a setup that makes good chambers, but I want to check every chamber to make sure they’re on size and correct. I have snap gauges, but prefer an inside mic.

I think I’ll just do some playing and see what I like best. I just thought I’d see what others are doing.

Thanks

You could also use a Tubing/Ball Mic
Most of us that turns necks own one
1. Measure outside to outside of the tenon threads with a standard MIC to find Tenon O.D.
2. Measure inside of chamber to OD of tenon threads with Ball Mic then multiply by 2
and subtract this number from the Total OD of the Tenon
=
The resulting number would be your chamber ID