Datum Dial Ammunition Measurement System


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JimKirk
December 11, 2012, 07:43 PM
Walkalong... F. Guffy ... others

Another product to measure... "Datum"

http://www.forsterproducts.com/store.asp?pid=37195&catid=19938

Looks handy but has a price!!

Instructions: http://www.forsterproducts.com/client_images/catalog19938/pages/files/Datum_Dial_Instructions.pdf

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blarby
December 11, 2012, 07:45 PM
Looks like a precision mic, with a cylinder........

NeuseRvrRat
December 11, 2012, 07:48 PM
it's simply a comparator

JimKirk
December 11, 2012, 07:57 PM
Yep... That is why I said "Another"....

Walkalong
December 11, 2012, 07:59 PM
Cool.

cfullgraf
December 11, 2012, 09:59 PM
Looks like the same method used by the Sinclair Bump Gauge but with the ability to cover several different diameter.

Looks interesting.

fguffey
December 12, 2012, 01:57 AM
As I have said before, I make datums, I collect datums, I purchase datums. pricy? I did not see a price, when someone has something for sale the first thing I want to know is ‘HOW MUCH?’ They have no way to make a good enough sales pitch to keep my attention if I do not know the price.

I am making a 50 Cal chamber length gage and case length gage, it is not going to function as I first planed, check the length of any 50 Cal chamber from the bolt face to the shoulder (datum?) of the chamber and measure the length of the case length from the head of the case to its shoulder on fired cases, partial neck sized cases and full length sized cases, then measure new unfired ammo case length and the length of cases that have been sized and loaded.

What does a datum cost? Again, I was at the Dallas Market Hall Gun Show when I approached a table, I said “DATUMS”. The Dealer at the table said he did not have datums. The shopper ahead of me ask “WHERE?” The shopper behind me ask “What does a datum look like?” I make datums, they are free, understanding the function of the datum as in ‘measured from’ is a concept that does not come easy for reloaders to understand, as L Willis tools, Sinclair? Hornady case length gages/comparators prove, the tools are nice but not necessary.

A few months ago I visited a machine shop, they were eat up, I offered a suggestion, and they said something like if you are so smart etc., etc.. seems they had worked on something for 2 weeks, after I explained to them what they should have known they were finished in 15 minutes. Then I walked over and suggested to one of the machinist ‘what ever you are doing you are doing it the hard way’. He said they were the only shop in town that did “that work” because it was labor intensive, I explained to him I made a tool 35 years ago that would cut the time to do it correctly and in far less time. I informed them I gave the tool away, seems back then they did not have time to do it correctly the first time and always had time to do it over.



Jim Kirk, “Another product to measure... "Datum" I am not politically correct, I purchase datums, I use datums to measure the length of a case from the head of the case to its shoulder. I measure from the round hold/circle flat surface to the head of the case. I do not have a tool that measures datum unless it is a hole gage. I measure the length of a chamber from the bolt face to shoulder of the chamber, the tool I am making for the 50 Cal will have a datum/round hole the case shoulder will sit on at the the top of the tool, the measurement I make from the flat surface to the head of the case is not ‘the datum’ my reading will be the length of the case from the flat surface to the head of the case.

Head Space: I have chamber length gages, head space is the length of the chamber from the bolt face to the shoulder or the datum. I make chamber length gages.

I will mail the 50 Cal tools in a few days, there will be no mention of Sammie and his specifications, there will be no mention of head space, transfers, standards and verifying, that is a different matter.

F. Guffey

howlnmad
December 12, 2012, 03:20 AM
I like their idea but it's a bit pricey.

Dentite
December 12, 2012, 12:07 PM
The price is pretty clearly marked...$157 MSRP for the full kit with two "dials". Other options available to split up the full kit.

I'm using the Hornady bullet comparator for seating depth and it works for me. This looks nice but looks to be a bit more bulky on the calipers.

NeuseRvrRat
December 12, 2012, 04:32 PM
I'm using the Hornady bullet comparator for seating depth and it works for me.

you can also purchase inserts for that comparator that will measure off the shoulder. that's what i use.

Ken70
December 12, 2012, 05:09 PM
Only the Lee Modern Reloading, both editions, shows the datum dimension.Sierra, Lyman, Hornady, nothing. If you have a small metal lathe, you can make these gauges. That's what I do. I know the "experts" will go berserk, but I measure the datum line on my ammuntion and compare it to the spec. If it's within a .001" or so, that becomes my headspace gauge.



Forester is really proud of their stuff, if you know what I mean, and I think you do. I have their case trimmer, got it used at a gun show for a good price. Never would pay retail for it.

JimKirk
December 12, 2012, 08:06 PM
Thought you'd like that ...Frank ... !!

The price is right there... $157 ... too pricey ... but it looks nice...

Forster's term:

Datum
A reference plane, point or diameter that provides a base for
measurements and calculations.

fguffey
December 13, 2012, 01:48 AM
Jim Kirk, thank you for the link, I am not commercially oriented, there are enough forum members trying to help other reloaders spend their money, they do not need me chiming in. As you said “NICE” I agree, but not necessary. The tool I made and gave to a friend in a machine shop doubled as a case length gage.

“Datum
A reference plane, point or diameter that provides a base for
measurements and calculations” and I collect datums, I make datums, I purchase datums for years, never once did someone ask “Is there something about a datum I need to know or do not know?

For years reloaders posted a drawing with an arrow pointing to ‘the datum line’, to all that made sense, the drawing is still in use today as if to say ‘that is all you need to know., and that is the point, if a reloader understands “THE DATUM”, WHY CAN’T THEY MAKE A FEW OF OF THESE TOOLS OUT OF (almost) NOTHING!.

F. Guffey

JimKirk
December 13, 2012, 08:02 AM
I make my Datum measurement tools out of hex nuts ... I usually measure through a few to find more uniform ones... works just like any of the other devise as it measures a datum....

I take the hex nut and drill the correct hole size ... zero out the caliper just like the instructions for the Forster devise ...

i posted what Forster's terms were for "Datum" ... for a simple explanation ...

kelbro
December 13, 2012, 08:21 AM
I can use a lot of spent cartridges to determine where the datum is for $157 :)

fguffey
December 13, 2012, 10:24 AM
“Only the Lee Modern Reloading, both editions, shows the datum dimension.Sierra, Lyman, Hornady, nothing. If you have a small metal lathe, you can make these gauges. That's what I do. I know the "experts" will go berserk, but I measure the datum line on my ammunition and compare it to the spec. If it's within a .001" or so, that becomes my headspace gauge”

I never know who I am allowed to disagree with:

I collect datums, I purchase datums, I make datums, I purchased two boxes of what appeared to be junk and miscellaneous parts, old parts at the Big Town gun show in Mesquite, TX, 40 lbs. $20.00, every old part in the boxes had a hole in it, attached to the holes were dies, case holders for case trimmers, etc.. to make the deal worth while there was a RCBS collet bullet with a 30 cal. collet ‘stuck’ in it. AND! There were Lee dies, to save weight I started sorting/separating the Lee dies in an attempt give them back (for free) The dealer would not allow returns??? He claimed he threw the Lee dies in with the deal?

Point? A lathe is not necessary, R. Lee’s book on modern reloading is a source of information for the diameter of the hole to be drilled in a flat surface, SAMMI is the original source. The datum/hole for the 308 W is .400 in diameter, the datum/hole for the 30/06 is .375 (3/8”). Again, I am not politically correct, I can use the .400 datum/hole for both the 308 W and 30/06, it is much easier to find the .3/8”/.375 hole than the .400” hole, I do not insist the diameter of the hole match Lee and SAMMI references. I make DATUMS, my chambers, my cases, All I have to keep up with is the index .000’.

A lathe is not necessary, nice but not necessary, the diameter of the hole? Not necessary to match LEE/SAMMI specifications unless the owner of the hole wants to compare the length of the case/chamber with LEE/SAMMI specifications.

Short cut: Fire formers chamber a case of unknown length and then pull the trigger, the case when ejected becomes a transfer as in transferring the chamber dimensions/length to the datum based gage. Had the fire former measured the length of the case before firing from the head of the case to the datum? then compared the length of the fired case with the minimum length/full length sized case they would know the effect the chamber had on the case when fired, This works for all but those that have cases that jump back, snap back or spring back, hammering my cases causes them to loose their memory, my cases have little to no recall as to what they were before being hammered from the inside out.

F. Guffey

fguffey
December 13, 2012, 10:41 AM
“I make my Datum measurement tools out of hex nuts ...” As we have agreed on before (Unclenick), a hole/datum with a radius drops the ‘plane’ (measured from surface) below the hole, back to LEE/SAMMI, the diameter of the hole/datum can be between the diameter of the shoulder between the shoulder/neck juncture and the case body/shoulder juncture, the diameter does not have to be ‘ACCORDING TO LEE?SAMMI’ again, I make them up.

Good affordable datums, a wire gage index plate, a bolt diameter gage plate, metric and standard, metal/plastic, and as indicated a reloader can have one for $150.00+- that is made in the form of a turret. I have fixtures for drills, in-line, triangle, flip dividers in handy carrying case, square and round, again, there is no shortages of datums around here. Again, this stuff does not drive me to the curb.

F. Guffey

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