Hornady Cartridge headspace gauges

John Kielly

John Kielly

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I am confused.

I recently bought a set of these ex-Stoney Point gauges as my recent .308 W chambers have been a tad tighter than my gunsmith set them up over the last 5-6 years. It's not an issue - it just takes a bit more fiddling to squeeze down all the old brass.

Anyway, as it happened, I decided to christen a few boxes of new Lapua that I've had lying around, for special matches, as you do. Anyway, gauging them before & after firing with the recommended .400" insert, I find that the buggers measure .005-6" longer before firing than after. I haven't got around to trying them with a different insert - the next size smaller would go over the neck & measure somewhat further up the shoulder - but this defies what I expected from loads that are not in any way squibs, (I'm tossing 208 Hornadys at around 2710 fps). The problem is that this gauge doesn't seem to give me any guidance about what bump I need to set my body dies to.

Any suggestions or solutions?

John :confused:
 
Good morning John!

Don't get too excited over what the differences in the "head clearance" is between new and fired brass. The shoulders may or may not be EXACTLY right, so the placement of a .400" bushing may locate a bit differently.

An quick and dirty way to determine the head clearance, place a piece of Plastigage on the case head, chamber it, then measure the gage. I'd start with the .001"-.003" (Green) and then the .002"-.006"(Red) if necessary. Plastic gage is available at most auto part supply stores.

You could cut shims for a GO - NO GO type measurement, but the Plastigage is quicker and just as accurate.

Bill
 
Bill hit it right on. Virgin brass is not concentric or perfectly round in the shoulder. Evidence of this is when you neck turn it down to the shoulder and it cuts more on one side or further down than the other. Your headspace gauge will not accurately measure brass until it has been staightened and blown out to the full size of your chamber after the first firing. This will give the shoulder a more uniform angle and diameter to measure on.
 
John ...

John Kielly said:
I am confused.

I recently bought a set of these ex-Stoney Point gauges as my recent .308 W chambers have been a tad tighter than my gunsmith set them up over the last 5-6 years. It's not an issue - it just takes a bit more fiddling to squeeze down all the old brass.

Anyway, as it happened, I decided to christen a few boxes of new Lapua that I've had lying around, for special matches, as you do. Anyway, gauging them before & after firing with the recommended .400" insert, I find that the buggers measure .005-6" longer before firing than after. I haven't got around to trying them with a different insert - the next size smaller would go over the neck & measure somewhat further up the shoulder - but this defies what I expected from loads that are not in any way squibs, (I'm tossing 208 Hornadys at around 2710 fps). The problem is that this gauge doesn't seem to give me any guidance about what bump I need to set my body dies to.

Any suggestions or solutions?

John :confused:
Click to expand...

When I neck up my Lapua 220 Russian brass using a K&M neck expander for my 6PPC AND when I neck up my Lapua 6mmBR brass for my 30BR they always measure LESS than their original length. Also, when I further fireform them, they again measure LESS than the after expanded length. This is normal when necking up with an expander and/or after fireforming.

New subject.

I also use the #400 insert for the .308 Winchester I have. I measure from the shoulder to the head of the case after deprimeing but before full length sizing. I then set my F/L die so I push the should back .002" [from that earlier measurement] or as close as I can get to that figure. I always use the same #400 insert for that purpose since it was designed for that size cartridge. I use the same insert for consistency in all my .308 Win measurements. Hope this helps. :)
 
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I think these tools are actually named incorrectly... they should be called cartridge head clearance gauges...

Head space is something set by the gunsmith when the barrel and action are assembled. It is measured/checked using fixed steel gauges. (go, no go, field)

Head clearance is what you measure when you measure fired and unfired cases.

Terminology is important but often ignored by manufacturers.
 
Thanks, folks.

I'm kind of happy that you've convinced me that I'm not crazy. I might reconsider what I said about my gunsmith's dies, too. Maybe these days he's just cutting with a die that has a tad different shoulder angle than before.

John
 
Terminology

Dennis .........

I thought about using the name Cartridge Shoulder Clearance Gauge instead for our "Digital Headspace Gauge", but the marketing guru said to go with a similar name to what Hornady is using.

I like the idea of comparing handloads to a fireformed case (at the shoulder), because your fired case is like a casting of YOUR chamber. The measured "difference" is displayed showing which way (and how far) to set your die height accurately. The ideal setting is -.001" to .002" for a bolt gun, and -.003" for gas guns.

- Innovative Technologies
 
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