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SGJennings
08-05-2009, 09:28 AM
How do I *accurately* measure the neck cut by a brand-spanking new reamer? Both the diameter and the length? For the purposes of neck turning and trim length.

Greg J.

Wilbur
08-06-2009, 09:40 PM
Two ways I can think of:

Measure the reamer.

Make a casting with cerrosafe.

___________________________

Try to resist making cases that precisely fit. It's dangerous and doesn't buy you anything.

alinwa
08-06-2009, 11:01 PM
Here's a linkie to a pic in post # 58 in thread "Al's 6X47L" http://www.benchrest.com/forums/attachment.php?attachmentid=7052&d=1233285377 which shows a tool I made for this. The tool is made by cutting a hunk out of the neck leaving the front (casemouth) ring alone and inserting a bullet backward.

If it's not intuitive I can 'splain it.

hth

al

SGJennings
08-07-2009, 09:04 AM
Thanks, guys. I appreciate it.

Wilbur: I'm glad you said that. The whole point that I'm trying to do is make dang sure that I have clearance.

Bob Kingsbury
08-07-2009, 11:46 AM
The length of a chamber as cut, can be determined, by making a brass plug.
The diameter should be very near the neck dia of the reamer. This would
be .261 in a .262 chamber. That diameter only for about .030-.040 long with
no real chamfer on the end, but not sharp. The remainder of the plug is turned to bullet dia and seated long in a case that has been shortened. Unlike
steel plugs made for this purpose, it wont hurt or scratch the chamber.It is
at times hard to sort these numbers out of a reamer print, and sometimes a
print is not available. As for dia., reamers can be measured(very gently) but that does not take everything into account. Pin guages can be made of brass,aluminum, or hardened steel. Soft steel can scratch, unless polished well.
or when turning necks , a case that shows a line around , at the bullet base
is every indication of what neck dia is. Benchrest chambers do not normally
have any taper to the neck, but many other calibers do. The 223 would be a good example. So neck dia can be kinda iffy.

SGJennings
08-07-2009, 12:16 PM
The reamer is to cut Mike Ezell's 30 Major, *except* that it's .332 instead of .330. Not relevant to this discussion, but it has .010 FB while Mike's which is based on the Robinett has zero FB.

It's a brand-spanking new reamer.

In fact, it hasn't even been delivered yet. It's in route via UPS. They say it's in Hodgkins, IL and has been there for over 12 hours. I don't know whether to be torqued because they're getting behind schedule or because their tracking is the pits.

wolf gray
08-07-2009, 03:08 PM
If they deliver it to you, not broken, not lost, not run over by the truck(I have received packages with tire tracks on them!) I would consider that you did good! Since it is a reamer in a small package they can probably throw it quite a ways, so you might get it a little quicker than a bigger package that they can't chunk as far :D

Best,
Dan Batko

"Where are we going and why am I in this basket?"

chillippr
08-07-2009, 03:21 PM
I assume (I know - that makes an ass out of you and me) that the chamber length of a properly headspaced chamber is the headspace allowance (very, very small) plus what the reamer print shows. I measure the chamber neck diameter with a small hole gauge and a micrometer which is the best I can do with the equipment I have.

alinwa
08-08-2009, 01:00 AM
I assume (I know - that makes an ass out of you and me) that the chamber length of a properly headspaced chamber is the headspace allowance (very, very small) plus what the reamer print shows. I measure the chamber neck diameter with a small hole gauge and a micrometer which is the best I can do with the equipment I have.

Chili......... it's thinking like this that'll get somebody hurt. IMO this method IS NOT safe.

Never assume.

Measure, or find someone who can.

al

Al Nyhus
08-08-2009, 08:01 AM
Here's a simple gizmo that can tell you both: it's a piece of alum. that is drilled and the piloted reamer run into for just a bit of the chamber length. Then, the outside is milled away...but not exactly in half...leave enough of the outer radius so the case neck so is well supported. This gives a visual for the neck length and allows a pin guage to be inserted into the neck for accurate neck diameter measurements.

Stan Ware makes these for me before he chambers a barrel with a new reamer we've never used before....just to make sure where we're at and to catch any 'tolerance' wander from what the print shows. Better to catch any issues on a piece of alum. than on a new barrel. 'ya know? ;)

Like Ronald Reagan said: "Trust, but verify." :D

Not the greatest of pics, but hope you get the idea. -Al

http://img.photobucket.com/albums/v467/tenxal/guage.jpg

chillippr
08-08-2009, 01:47 PM
Alinwa

We canít exist without assuming.

I assume that Dave Kiff is grinding my reamers within tolerance in accordance with the reamer prints he provides me and that he has a QC/QA system in place to assure that.

I assume that the premier benchrest gunsmiths that do my chambering are in fact capable of using these reamers to cut minimum sized chamber in my barrels.

I know that you can cut an oversized chamber with a reamer, but I do not think you can cut a chamber that is undersized with regard to any of the reamer diameter dimensions or the reamer neck length dimension.

My case lengths are always held .010 under the reamer print chamber length dimension. I believe holding case lengths under the chamber length is generally accepted procedure.

My case necks are always turned so that the loaded round neck diameter is at least .002 under the reamer print chamber neck dimension.
I believe holding loaded round neck diameter under the chamber neck diameter is generally accepted procedure.

Pin gauges are certainly superior to the small hole gauge/micrometer for measuring small bores, but I believe the small hole gauge/micrometer properly used will indicate if the neck diameter is significantly undersize due to an error in reamer grinding.

alinwa
08-08-2009, 01:59 PM
Alinwa

We canít exist without assuming.

------I assume that Dave Kiff is ........

------I assume that the premier benchrest gunsmiths .........
I know that you can cut an oversized chamber with a reamer, but I do not think you can cut a chamber that is undersized with regard to any of the reamer diameter dimensions or the reamer neck length dimension.

------- I believe holding case lengths under the chamber length is generally accepted procedure...........

-------I believe holding loaded round neck diameter under the chamber neck diameter is generally accepted procedure..................


-------I believe the small hole gauge/micrometer properly used will indicate if the neck diameter is significantly undersize due to an error in reamer grinding.................


Sorry Chillippr, we see this differently. :)

I don't assume and my "beliefs" must be verified by actual factual observation.

'course, this is just ME...... when I've got a controlled explosion detonating 8" from my right eyeball.

I also look both ways before crossing an intersection, twice or three times.

Nope, I don't assume.

al