Has anyone seen this?

alinwa said:
Well, generally 1/10 inch of depth equals a thou of taper in my chambers so for myself, I like the gage engagement to be essentially equal between chambers. When I get a variance of say .050 in depth I can "assume" that there's at least a half-thou (5 tenths) difference....but definitely A DIFFERENCE.....
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OK, I made a quick [approx] .200” datum gauge. I pulled two barrels from my barreled actions. I measured HS, the approx midway body point and the approx .200 point. The gauges don’t sit perfect in the tapered chamber so I understand there is error. I ran the measurements twice to get a better average. The mid point gauge had about a .005” depth difference between the two random chambers. HS was about .0005” (may or may not have been intentional, these chambers were for different actions). The .200” point had maybe .002” depth difference. I’m no math magician, but it’s looking to me like the chambers are pretty close to “identical”. I’m pretty confident that brass from these two barreled actions would easily interchange.

This test is certainly not scientific, and I still will not guarantee a .00025” dimension on anything. I will say that I feel my chambers are as dimensionally accurate as any. You turn knobs, and there’s nothing wrong with that. I have servos instead of knobs. The work is the same.
 

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Rubicon Prec. said:
OK, I made a quick [approx] .200” datum gauge. I pulled two barrels from my barreled actions. I measured HS, the approx midway body point and the approx .200 point. The gauges don’t sit perfect in the tapered chamber so I understand there is error. I ran the measurements twice to get a better average. The mid point gauge had about a .005” depth difference between the two random chambers. HS was about .0005” (may or may not have been intentional, these chambers were for different actions). The .200” point had maybe .002” depth difference. I’m no math magician, but it’s looking to me like the chambers are pretty close to “identical”. I’m pretty confident that brass from these two barreled actions would easily interchange.

This test is certainly not scientific, and I still will not guarantee a .00025” dimension on anything. I will say that I feel my chambers are as dimensionally accurate as any. You turn knobs, and there’s nothing wrong with that. I have servos instead of knobs. The work is the same.
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so does the .200 diameter measure match the written reamer diameter dimension?
 
I take that back. I had a .030" chamfer on the front of this gauge and I didn't program any tool nose compensation. I just flipped the gauge around so the "head" side went in first and measured the total thickness of the gauge.

The gauge is so short, it is very hard to get it to drop in square. Because of this, the depth mic measurements varied the a bit, but it looks like it's about .009" of where it should be compared to the HS measurement. What's that? Maybe +/- a tenth in diameter variance from the print? It's certainly close enough that I'd call it "on size".
 
I know one barrel maker that has to hold chamber tolerances, now I don't know what those tolerances are, in 10 different places using gage balls. They've been doing it for years for this customer.
 
I had not looked at this before today. I think, if I wanted to do this (and I don't), I would just do a chamber insert with a short thread at the base (set in with a pin wrench). Should accomplish the same thing. Regards, Bill
 
Bill that sounds like a simple method but it makes me wonder if you'd end up with excessive case web expansion? I'm recalling Gene Beggs work with indexing barrels and using a bushing with a differential thread to accomplish the indexing. As I recall Gene had issues with excessive case web expansion resulting in sticky/clicky cases. Back then Jerry Stiller was around and he provided some insight into the problem. The issue was reduced hoop strength caused by the small but present stacked clearances in the tenon and bushing. I think (???) this issue caused Gene to ultimately abandon the differential thread bushing idea. Maybe a tightly fitted insert would avoid this but maybe not???
 
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Dave Tooley said:
We all know written VS actually measured in a metrology lab are two different animals.
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AFAIK a metrology lab uses exactly the same optical comparator Kiff uses. I know everyone here loves to bash David Kiff and PTG but I'm not "everyone" and all of my Kiff reamers cut right on. EVEN THOSE that have been sent out to various gunsmiths who bashed them claiming they "only cut on one flute" and "were over-sized" and "chattered" and "Kiff can't get his numbers right twice't in a row"......

I've got 5 6BR reamers and 8 WSM reamers alone, a number of which have been vilified by different people but which FOR ME do exacting and completely repeatable work.

I'll shut up now as urinating contests aren't my bowl of jello.....


Wsnyder, I completely agree with you. And I've done "home testing" using large and small tenon Savages chambered in 300WSM, 338RUM and 338Lapua that prove to me (I'm not a metrology lab) that tenon expansion is a thing.....and that furthermore IMO the "second sleeve" or containment of the receiver ring does nothing to support the tenon. It is my opinion that a stack of sleeves does not in any way approximate the hoop strength of a solid cylinder of steel.
 
Dave Tooley said:
I thought we were talking about cutting Identical chambers? Guess I was misinformed.
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The problem is is...... I live in my own head :)

In twenty+ years of discussing the problem of the making identical chambers, and in 15yrs of NOT GETTING identical chambers from various people, there's been a lot of reasons advanced. A lot of excuses.......

A large preponderance of my discussions since I've solved the conundrum for myself have revolved around "Gordy Rods" and "pushers VS floaters" and etc etc..... all geared at the same thing. Cutting identical chambers.

I now have no problem making identical chambers, but it's certainly neither quick nor easy. Nor do I see a way it can be done quickly and easily. Nor do I have a poor understanding of either metrology or modern machining practices.

I've never had repeatable work done by anyone using CNC equipment. Just excuses.

As far as bashing PTG, it's just fashionable on this and the other "accuracy" shooting board. I'm sticking up for PTG as a matter of habit. ;)
 
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