Comparator tools for measuring at the ogive and the shoulder datum line

Jasbo said:

I use Sinclair for Headspace and Hornady; for Stoney Point style measure of maximum CBTO and to setup seating dies for CBTO. Good points made regarding Hornady aluminum bushings! You must use the same bushing for all CBTO measurements to have meaningful comparisons.

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I have a second set that I put on the other anvil when measuring, for lack of a more accurate term, "bearing surface". ALWAYS keep them separate. Have both sets marked as a set so I don't get components swapped between the two sets.

Jasbo said:

I use Sinclair for Headspace and Hornady; for Stoney Point style measure of maximum CBTO and to setup seating dies for CBTO. Good points made regarding Hornady aluminum bushings! You must use the same bushing for all CBTO measurements to have meaningful comparisons.

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That is all CBTO measurements of the same caliber bullet correct?

tribb said:

That is all CBTO measurements of the same caliber bullet correct?

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Roger that.

Tiny Tim said:

This is the kind of precision needed to make them interchangeable, and most would be unwilling to pay the price for that level of precision, especially for multiple inserts.

Sounds like you've given this some thought. Great ideas!

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I might spent a little time thinking about it, but this is the sort of problem that is part of my job.

K.E.C. said:

Check out Creedmore Sports. Com.
One gauge does most common calibers.
Been using for a few years.

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I have a "nut" like that, do not recall where I bought it. I find that the edge break performed on those holes is uneven and makes or allows the assembly being measured to wobble in the calipers.

ntsqd said:

I might spent a little time thinking about it, but this is the sort of problem that is part of my job.


I have a "nut" like that, do not recall where I bought it. I find that the edge break performed on those holes is uneven and makes or allows the assembly being measured to wobble in the calipers.

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Well thank goodness a "Nut" doesn't make Creedmore Sports tools.

Never met him, wouldn't know.

I take a piece of the barrel cutoff, chuck it in the lathe, face it off on both ends, run the reamer in enough to get a full shoulder. I use them as a gauge to check that bullets aren't too long and as a gage to measure case length to the shoulder. I have one for each rifle that I chamber

I have the area 419 set up and there adjustable shell holder set up
Not cheap but there are accurate

I have three. The Hornady is referenced to the datum point only. Basically, a 008 chamfer and a cylinder. I use a go gauge with length embossed on its side. Knowing that, and then measuring after zeroing calipers gave me the 008 aluminum gauge chamfer to extract absolute values vs SAAMI specs. I think Short Action Customs makes the better of my three because they have a taper to match the spec of your brass' shoulder, but I …think.. has a much-needed rounding at neck/shoulder interface. They were snotty to me on the phone; not answering any general questions about basic design info. In fact, one of the most rude conversations I've ever had with a manufacturer; maybe I caught the guy on the wrong day. That being said, they're great comparators. The third is my LE Wilson headspace gauge and LE Wilson case micrometer. It fails where the other two are consistent. I believe its failure is due to the abrupt edge in machining at shoulder/neck interface. With my unfired brass, up to 003 shorter than desired headspace, all measures accurately between all 3 gauges. Once the brass is fired and deprimed, The Hornady and SAC show mild 002 headspace growth, whereas the expensive LE Wilson shows 007 growth, because there is some deformation at the shoulder/neck interface which interferes with their abrupt junction. The full length resizing die cannot resize once fired brass yet, because it is still too short for my desired final brass headspace. I suspect that when resizing after 2 or 3 firings, the LE Wilson will measure fine. I like the feel of their case micrometer gauge.

Lots of good info here…ChrisinKY nailed it though. Great spot to over spend.

The measurement doesn't matter as long as it's consistent. I have two Hornady sets and make sure to keep them separated and a nut. I never really liked the nut and use the Hornady. If the hole isn't square there is only one way to ensure consistency and that's making sure you put the insert in the same every time. You can see where the set screw engages and make it engage at the same spot every time you switch it.

I get a new barrel I make a dummy round, that is thrown in the die box and my notes. Everything from that day forward is based upon that dummy. So if I switch calipers or comparators, I can go back to the dummy to establish my baseline.

ntsqd said:

I have the Hornady kit, less than impressed. I've given some thought to making my own insert bushings. The holes would be reamed and then honed to a specific size and the faces would be exactly square to the hole centerline with no edge break unless I can figure out how to precisely and consistently create a .005" radius that is economical to do.
I doubt that I'd make them from aluminum. 17-4 PH or lightly hardened A2 would be my initial choices for metal.

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If you figure out how to machine that radius, and end up with some free time, I'd be interested in purchasing a set of finely-machined bushings.

I've been using a hex style comparator for many years now that I bought from Sinclair! I see Brownells is selling it for $24.99. I wouldn't reload without it!
I have a folder in my computer with comparator measurements for every rifle I own using every different bullet I shoot in each rifle. I normally measure a number bullets because the ogive tends to somewhat vary on each bullet up to .002 to .003 thousands and I keep all those measurements then use the average to know where the bullet would touch the lands. If I buy a new box of that bullet, I take their measurements all over again because it'll be a different lot!
I used the Sinclair OAL Gauge (mybe it was a Stony Point Gauge, I don't really remember) along with their modified cases to measure the comparator length but eventually broke the OAL Guage -- and when Hornady bought the rights to make it, I bought their Hornady Lock-N-Load OAL Gauge --which is the same gauge!

tribb said:

This is all new to me have a 4 decimal Mito. To work with. Use the Hornady or Stony point system or the Forster system shown in Midway USA. I have a picture here . Click on it for better look thanks Tribb

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I checked out your Forester Datum Dial Ammunition Measurement system and it certainly looks interesting, especially because of the ability to measure the datum line of shoulder stretch on a case! It looks like I'll have to put it on my wish list but for now I'll stick with the Sinclair Hex gauge because of the expense of the Forester system. But thanks for posting another tool of which I wasn't aware -- but is now in my future for my reloading bench!

One trick I have used is to chamfer the aluminum inserts made by Hornady with your case neck chamfering tool.
It makes them a lot more consistent.