Hornady Headspace Gauge

[PMA3]

I set the gauge up with the Body/Bushing on the lower caliper blade and then attached a Davidson base (sold by Sinclair as part of the Davidson comparator) to the top blade for a more uniform alignment of the case. I took five 7 mag fired cases and measured them...they measured 4.327"-4.328". I then took the next five cases in the box and neck sized them with a Wilson bushing die...they measured 4.328"-4.329". I know the Wilson die does not touch the shoulder or the body, just the neck. Why did the neck sizing INCREASE the case size? Shouldn't these cases measure the same as the fired cases since the shoulder wasn't bumped? Confused in PA.

 

[fguffey]

http://www.saami.org/PubResources/CC_Drawings/Rifle/7mm%20Remington%20Magnum.pdf

Nothing about the 7mm mag measures 4+ inches. I will assume you are using a comparator, when I use a comparator to compare case length from the mouth of the case to the case head or from the datum/shoulder to the head of the case I zero the gage and then compare the fired length with the sized length.

I do not measure case head space length, I measure case length from the datum to the case head. If your die does not touch the shoulder of the case and you are not bumping?

Neck sizing, when the neck is sized down the neck gets longer, when the expander ball is pulled through the neck the case neck gets shorter. I will assume you are measuring case length from the mouth of the case to the case head..

F. Guffey

 

[wrangler5]

For general reference, the Hornady headspace gauge with a 330 insert (for 223, among other cartridges) plus the hornady base/anvil, together measure 2.154 when attached to my Starrett dial caliper. So any case measurements I make are in addition to that. I'd guess that's where PMA3's numbers come from.

 

[bigedp51]

I'm going to pull a fguffey and use a feeler gauge trick with the Hornady cartridge case headspace gauge and get true headspace readings.

Below a Colt Field Headspace gauge.

Below the Colt gauge in the Hornady gauge reading actual cartridge headspace.

Fired case from my AR15

The same case with .003 shoulder bump.

So "WHAT" is the point of mixing Sinclair and Hornady body parts??? You just made a Frankengauge using mixed body parts.

All you have to do is spin the cartridge and let it self level.

 

[bigedp51]

Neck sizing, when the neck is sized down the neck gets longer, when the expander ball is pulled through the neck the case neck gets shorter. I will assume you are measuring case length from the mouth of the case to the case head..

F. Guffey

fguffey
Have someone in your house pull on your neck and see if it get shorter.

If you can't do that then ask Saddam Hussein's cat if his neck got shorter.

Below is a average run of the mill RCBS expander button used in a standard die, I don't care what type lube you put inside the neck. Pulling this expander button through the case neck is going to be like watching a Uniroyal Tiger Paw commercial and watching the expander ball "grip the road"!!!!! (meaning it will make the neck longer) :

Uniroyal tires Commercial
http://www.youtube.com/watch?v=BBOS_AS08Bc

 

[PMA3]

The Wilson die does not have an expander ball to screw up the neck that I just sized to the dimension I want; therefore, there should not be any stretching (elongating) of the case neck. The Davidson base is used so that the case alignment (from blade to blade) is the same for each measurement....no wiggle room for the case head to slide along the top caliper blade. If I bumped the shoulder back, I would expect to get a lower reading like the AR pics display (1.467 to 1.464). But since the die does not touch the body, bump the shoulder or expand the neck, the higher rather than the same measurements are baffling to me.

 

[Brians356]

PMA3,

Why did you ask if your measurement setup was kosher? Oh, wait ... you didn't ask that, did you?

Seriously, I, too, am curious how sizing the neck only (w/ no expander) could set the shoulder forward.

However, I am concerned that the observed change was only 0.001", which is kind of "down in the noise" when using a dial indicator with attachments at both ends of the case. Usually, I can get the indicator needle to move at least that much just by varying the squeeze pressure on the stack. If you'd said 2 or 3 thousandths, I'd be more impressed.

 

[PMA3]

brians356,

Good point. A +/- .001" could be the best reading to expect from the Hornady gauge, regardless how you secure the case head....and five cases are a small sample.

 

[Bart B.]

Re: Nylon Headspace Gauge

Here's some pictures of how to use a 30 cent nylon spacer with a digital caliper to measure your fired cases then after sizing them to see how much their shoulder gets set back. Meanwhile, if there's an Ace Hardware store nearby, stop by it then buy a 1/2 inch long nylon spacer with a 3/8ths inch inside diameter. Then buy or borrow a digital caliper; a "must have" tool for reloaders in my opinion.

You'll also want to use these labels on your die so you can change its height in the press very precise to control how much sizing the cases get.

http://s860.photobucket.com/user/jepp2/media/DieAdjustment-1.jpg.html

Note the last picture shows the case to have its shoulder set back .001 inch so it measures 2.047 inch. Perfect for best accuracy, feeding reliably and long case life.

Here's some drawings of the .30-06 case and chamber that may help you see where the measurements I got came from. Note the "headspace" dimension for the chamber drawing:

http://www.saami.org/PubResources/CC_Drawings/Rifle/30-06%20Springfield.pdf

Note also that the diameter of the reference point on both the chamber shoulder and case shoulder is .375 inch; same diameter as the hole in that nylon spacer. And after you full length size several cases, there'll be a small spread (few thousandths) across their headspace measurements. You may need to reset the die so the longest one is no longer than that of the fired case.

 

[tenring]

I have the Hornady comparator and Davidson base and nose pieces for each caliber. I prefer the Davidson. The nose piece fits very closely into the base lip, and reads consistent accuracy.

Also, best tool to measure headspace is the Redding Instant Indicator. Unfortunately, they are caliber specific.

 

[Brians356]

Also, best tool to measure headspace is the Redding Instant Indicator. Unfortunately, they are caliber specific.

Yeah, those are nice. But at $90 per cartridge (plus a dial indicator), I can make do with my old Stoney Point gear, for everything. I use the bullet comparator with the .375" insert for checking relative shoulder movements.

Incidentally, I never knew until just today that the datum line for many of the .473" base cases is located by the same .375" diameter on the shoulder. I had only chosen the .375" insert because it was about the right fit on the shoulders, but it turns out that wherever it falls is pretty much where the datum line is for my 6mm Rem, 270 Rem, and 30-06.

 

[/VH]

PMA3,

I don't have an answer but I am curious; how much are you reducing the neck diameter from the fired diameter and what kind of lube are you using, if any? I am kind of thinking brians356 may be right about "lost in the noise".


brians356,

You mentioned a 270 Rem, is that made off of a RUM or RSM or something else? I have not heard of it, sounds interesting.

 

[PMA3]

Bart - Thanks for the very informative pictures and innovative procedure to measure head space. The Davidson base and Hornady gauge do the same thing but at a higher price. I do have a good pair of digital and dial calipers (Mitutoyo) that I use and I always measure ALL my cases first, then select the longest one.
tenring - Nice to see someone else uses the Davidson comparator system. Works great for the AOL measurements
to make sure your seating die is setting the bullet exactly where you want it to be in relation to the lands.
/VH - I use the Forster graphite kit with the 3 brushes and mica in the bottom and run the neck over the .30 cal brush into the mica. My cases are neck turned to .0125", fired case is .313", loaded round is .309", neck sized with a .305 bushing gives me .002" tension.

 

[/VH]

PMA3,

For clarification, because I may very well be wrong; you have described .002" neck tension being achieved by using a .004" smaller bushing than your loaded neck diameter. I have always understood .002" neck tension to be a condition where the sized neck diameter (not the bushing) measures .002" less than loaded neck diameter and is, at least in my experience, generally achieved by using a bushing that is .002" to .003" smaller than loaded nk. dia. This may be exactly what you are describing as well and if so; assuming that your .305" bushing actually measures very close to that dimension, there may be some serious spring in your brass.

I have, at times, had issues with getting varying measurements when measuring shoulder bump and neck diameter of sized brass as well and while I think some of it was due to the lost in the noise of my ability to measure issue mentioned by brians356 above, I have also noticed by the feel when seating bullets and re-measuring shoulder bump a day to a week or two after sizing, a difference in dimensions or seating force from freshly sized brass. I am convinced that some brass can continue to spring back for quite some time. This may be part of what you are experiencing.

 

[Brians356]

brians356,

You mentioned a 270 Rem

I wish I could call that a "typo", let's just call it geriatric brain cell attrition.

 

[PMA3]

/VH,

Spring back is definitely an issue. When I run the fired case (.313") in the Wilson die containing a .305" bushing, the newly sized neck diameter is .307", not .305". Besides spring back, the true bushing size could be different than stamped. This gun is used for long range varminting and I load volume at one time, trying to maintain constant parameters for all loaded rounds. For target guns, I anneal every time and load 2-3 days before the match, trying again to control as many parameters as possible....a different technique but the same principle.

 

[Brians356]

I have also noticed by the feel when seating bullets and re-measuring shoulder bump a day to a week or two after sizing, a difference in dimensions or seating force from freshly sized brass. I am convinced that some brass can continue to spring back for quite some time.

You are correct. I wish I could recall the article I read on this or another accuracy site, but the chap stated that residual spring-back is demonstrable. And it is plausible when you think about it - why should brass complete 100% of its spring-back inside one second?

It might not be enough to easily measure dimensionally (say a few ten thousandths - could be a lot more) but it should be fairly noticeable in neck tension and seating force. (I have a set of precision pin gauges in .001" increments, I should be able to detect it using those - if one size is a snug fit after sizing the neck, it will be apparent later if the neck relaxes a tiny bit.)

I'll see if I can find the article.

 

[Brians356]

I'm going to pull a fguffey and use a feeler gauge trick with the Hornady cartridge case headspace gauge and get true headspace readings.

Below the Colt gauge in the Hornady gauge reading actual cartridge headspace.

Question:

That Hornady comparator bushing (the silver part): Will it fit in my old Stoney Point body (which has been changed to red color by Hornady)? I.e. have the part dimensions changed at all?

Brian

 

[Brians356]

Also, best tool to measure headspace is the Redding Instant Indicator. Unfortunately, they are caliber specific.

Yeah, those are nice. But at $90 per cartridge (plus a dial indicator), I can make do with my old Stoney Point gear, for everything. I use the bullet comparator with the .375" insert for checking relative shoulder movements.

Incidentally, I never knew until just today that the datum line for many of the .473" base cases is located by the same .375" diameter on the shoulder. I had only chosen the .375" insert because it was about the right fit on the shoulders, but it turns out that wherever it falls is pretty much where the datum line is for my 6mm Rem, 270 Rem, and 30-06.

Correction: The Stoney Point / Hornady bullet comparator bushing marked "37" is for .375" bullets, but the lands in a barrel are smaller than nominal bullet diameter, and sure enough, the "37" bushing's hole is actually only .365". So when using it on the shoulder of a case it does not contact the shoulder near the SAAMI datum line, but farther towards the neck.

Nevertheles, it works fine for detecting relative setback of the shoulder (before/after bumping) but it is not even in the ballpark for headspace measurements.

The Hornady Headspace Bushing marked "375" should be used for "headspace measurements" (still inexact using a caliper and bushing, but close) or any spacer with a 3/8" (.375") hole, as suggested by Bart B.