How are guys measuring their "on size" chambers

[Shawnba67]

I can easily measure runnout on my own work, but I see the terms on size semi frequently. I know inside micrometers exist, but how can a guy accurately measure the inside diameters of a chamber and at the correct depths ect? Is this where cerrosafe IS the answet? That .200 line is hard to find, and I cant just look for the right number along the taper, because its a taper and the right number will be somewhere but if its not at .200 then Im offsize!
Thanks

 

[Larryh128]

I can't answer that and I'm not sure that many can or would attempt to, kinda like saying a barrel only has .0001 runout from end to end. I can guarantee you that it isn't being measured. I can tell you that you will never get an accurate/exact measurement on cerrosafe because it shrinks slightly. It's meant to identify an unknown chamber etc.

 

[Danny1788]

I just go off fired brass..... not close to what your asking.

 

[RWO]

Cerrosafe works provided you take your measurements according to the directions. It does shrink initially to allow withdrawal of the cast but then expands to exactly chamber size at 60 min. after cooling. See https://www.brownells.com/userdocs/learn/076-200-446_Cerrosafe.pdf

RWO

 

[DaveTooley]

Gage balls
A specified size ball at a specified depth.
Short of a CMM machine it's the only way us shade tree guys can do it.
I sometimes get prints that have a measurement for HS using a ball making contact with the shoulder.
And no I won't do all the trig for you.

 

[butchlambert]

I can easily measure runnout on my own work, but I see the terms on size semi frequently. I know inside micrometers exist, but how can a guy accurately measure the inside diameters of a chamber and at the correct depths ect? Is this where cerrosafe IS the answet? That .200 line is hard to find, and I cant just look for the right number along the taper, because its a taper and the right number will be somewhere but if its not at .200 then Im offsize!
Thanks

Is there a reason or are you having a problem?

 

[Shawnba67]

Removed errant remnant post left in on accident. Shawn

Is there a reason or are you having a problem?

No problems that i know of. Was just wondering how it is people ensure that thier chambers are really to the reamers spec. and not oversize. That means theres either a way to measure it, or its all smoke and hocus pocus. Was just curious.

 

[tobnpr]

^^^
This...exactly what I thought when I read the post...Why, unless a problem is suspected?
A chamber reamer is a form tool, assuming it was ground to the correct dimensions and if allowed proper "float" to follow the bore (with a properly fitted bushing) it will not cut out-of-round or oversize chambers.

 

[butchlambert]

I've never learned how to cut an oval chamber. I have a custom chamber reamer that I spec'ed to build a proper die. You might find that a tight chamber will make it hard to full length size your brass. A lot of ways to handle that, but a spec'ed under size die reamer works for me.

 

[Shawnba67]

^^^
This...exactly what I thought when I read the post...Why, unless a problem is suspected?
A chamber reamer is a form tool, assuming it was ground to the correct dimensions and if allowed proper "float" to follow the bore (with a properly fitted bushing) it will not cut out-of-round or oversize chambers.

How could you prove it?

 

[Someoldguy]

It's rather difficult to measure chamber dimensions to say, ".0001". Mr Tooley provided an example of the best method to measure chamber length available that I am aware of. As for diameters, there are a few different things one can do depending on what diameters are in question. Measuring after chambering before removal from the fixturing is the easiest way. Cerrosafe castings will provide the greatest number of measurement points in one casting that I am aware of after the machining process provided the directions are followed as mentioned above. The amount of precision is arguable, but probably no more than the change in measurements you'll likely see from holding the mic in your hand for 20 min or so while measuring.
And as Mr Lambert stated above, unless there is a suspected problem you are attempting to locate, none of this painstaking measuring really matters anyway. IMHO.

 

[tobnpr]

How could you prove it?

Excellent question...
I don't.
This is why, I don't buy used reamers....
Who, in their right mind, would buy this:
https://www.ebay.com/itm/Chambering...=true&nordt=true&rt=nc&_trksid=p2047675.l2557

I don't buy used (might, from a trusted source), will rent from 4D when needed, but otherwise every reamer in the drawers is laser engraved Manson, JGS, or PTG (though not so confident in the last one lately). You're trusting the quality of the chamber to the reamer- precisely because there's no way for most of us to "check" one to be sure it's ground to the correct dimensions. Shoving anything less down the bore of a $300-$500 barrel blank would be foolhardy.

 

[GenePoole]

Gage balls
A specified size ball at a specified depth.
Short of a CMM machine it's the only way us shade tree guys can do it.
I sometimes get prints that have a measurement for HS using a ball making contact with the shoulder.
And no I won't do all the trig for you.

Luckily, you only have to do the trig once, then just plug in the numbers. I did it here:

http://forum.accurateshooter.com/threads/go-gauge-alternative.3942012/page-2#post-37124103

 

[Intheshop]

I run a small hole gage in to check neck dimensions. With "touch" it'll also show any out of roundness,but that is a rarity.... on a rifle chamber,IME. Just wanted to point out the difference in gage pins and a small hole gage.

Anyway, that's an aluminum,2018? arrow and a wrap or so of electrical tape to get it perfectly snug on the knurled gage handle. Just way faster than chamber casting. And is a "check system" to go along with measuring before/after case dimensions. It's useful in cast shooting as we change bullet diameter,pretty much,"at will"...... but I've learned that you need to understand that while we may get lucky running __" of clearance,if you can learn to predict,why this much clearance "works" beforehand, all the better.

 

[TAJ45]

From shop set up/QC work checking experience, i found this an interesting exercise of "how would i do it?"
First thought would be a ball of known (here's the kicker) -appropriate dimension- dropped into the bbl then distance measured with a depth mic. This would at least give a tangency point from face of bbl + half of ball dia.
Yes, ya needs ta do sum trig. After all we be shhooters majoring in triggernometry, eh?
);
From my apprentice days, it seems the harder i pushed a reamer, the better chance of it cutting out of round or oversize. But being many, many moons ago - I could be mistaken.

 

[DaveTooley]

Gage balls are used to measure diameter also. I know on 50 cal P&V barrels the end user requires measurements in I think 10 places using gage balls.