Setting Headspace. Questions?

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baddarryl

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Hi. I am using "Top Grade Ammo" by Glen Zediker as my guide for reloading more consistent ammo. I am setting up a Forster Benchrest Die for my RRA LAR 15 in .223 using once fire LC brass. He suggests.004 less than measured using Headspace gauges for safe rounds.

My average over 10 cases is 1.463 with a low of 1.460 and high of 1.465. So less .004 from the average gives a target of 1.459. Does this seem good to you?

Also does this measurement change by using different cases? The reason I ask is I have brand new unfired Winchester cases that I am going to load for Hi Power rather than the LC for now anyway. I am going to resize that brass to match the once fired cases before I shoot it. Not really for the headspace as much as to fix the case mouths of the new brass. Thanks.
 
I would check that the head-to-shoulder length of the once-fired-in-your-gun brass isn't getting any of its height from a bend in the rim caused by extraction. One indicator is the height not measuring the same all the way around as you rotate the case on the caliper jaw. In that instance, the shortest result is closest to your chamber size. But if you are satisfied that the cases are not bent, the longest will be closest to matching your chamber headspace. You could take one and reload it a couple of times by neck sizing only and single loading and firing. That will tighten the measurement it takes off from the chamber.
 
Are you using this kind of tool?

https://www.natchezss.com/hornady-lock-n-load-headspace-gauge-with-5-bushings.html

If so, that is normally referred to as a CBTD measuring tool.

A headspace gage is normally this tool:

https://www.brownells.com/gunsmith-tools-supplies/measuring-tools/headspace-gauges/go-no-go-gauge-sets-prod26876.aspx

When a case fires, it expands to seal the chamber and then springs back. It you fire multiple times and only neck size, you can get close to true chamber size.

In an AR15, using a progressive press, I find 0.003-0.004” a good target as progressive presses can vary some in their sizing amount on rifle brass.

Die adjustment will vary some based on case hardness, not target dimensions.
 
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That gauge was originally invented by Stoney Point, who called it the Head Shoulders Gauge. Stoney Point later sold it to Hornady.

That gauge, like the RCBS Precision Mic, is what is called a take-off gauge. That is, it takes an indirect measurement of rimless bottleneck cartridge chamber headspace off a fireformed case. The limitation of that method is the brass is a little bit springy, and if the pressure is too modest the cases can come out several thousandths small and vary a bit from one to the next. If the pressure is high enough to produce sticky extraction in a bolt gun, the pressure is too high and the cases will spring out larger than the chamber upon extraction. But using neck-sizing-only for a few loads with a published maximum load, you will iron out most of the spring-back and get a pretty close-to-chamber-size measurement. If you do it with several cases, you can stop the neck sizing when they are all the same size or very close to that.

Also, a limitation of that gauge system is the aluminum inserts have an edge left slightly radiused by the bead blasting finishing process, so they don't exactly hit the SAAMI datum line around the shoulder and can be off a few thousandths. The way to calibrate one is to get an actual precision headspace gauge from Dave Manson or one of the other shops that specialize in gauges and reamers (don't buy the economical ones; I've had those turn out to be off by up to two thousandths) and apply the Hornady gauge to it to see how much error your insert's measurements have. Or, you can just ignore the error and collect measurements that only apply to your gun, which is fine as long as you don't assume they apply to other guns or you are not comparing them to measurements made by someone else with their uncalibrated copy of your insert, as they can also vary a few thousandths from one to the next.
 
Thanks again for the info, Unclenick. I should mention there IS, as well, a difference between the Stoney Point and Hornady bullet comparator inserts. I could not get an SP for my 6.5mm (.243) so I had to buy the Hornady set. If I insert and zero, e.g., the .25 caliber insert into the Stoney Point base, then replace it with the Hornady .25, the difference is 0.001" and requires re-zeroing.
 
Well I had a whole rant going on but thought better and erased it on CBTD or better known once as case or cartridge headspace . :rolleyes: either term still needs to be explained so why did we invent (CBTD) another one :confused:

The bent rim idea is not a bad idea to look for but I think a more important thing to be sure to do is make the measurements with the spent primer removed . Primers can have all kinds of deformations that can cause an inconsistent measurement so having them removed prior to measuring case headspace :p is always best .

IqHP8x.jpg
 
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Any time I read about a gas gun and trying to cut close to the dimensions I shudder.

I don't shoot one any more but I always pushed those shoulders back .005 from the max as a minimum and happy with .008 if it ranged up there.

I know an AR is extremely unlikely to fire out of battery, but you sure do not want a case that does not seat.

Gas gun issue is its really hard to test if the rounds are all going to chamber right.
 
If you have a minimum chamber on a Garand or an AR, what you find is it still shoots new commercial ammunition. That ammo is rarely more than -0.003" below chamber minimum dimensions, and more often -0.002" at the shoulder datum diameter. The reason that is adequate is the middle tolerance of the diameter of the new case is -0.005" below the middle chamber tolerance. Few cases are made at maximum. It's easy to forget resizing works on diameters as well as head-to-shoulder length. It is the reason that a gas gun that doesn't feed reloads reliably is often cured by the use of a small base die, which provides extra narrowing even if you don't move the shoulder back any further with it. Bottom line: check all your case and chamber dimensions and figure -0.002" on length combined with at least -0.003" on diameters will generally give you reliable feed.


IqHP8x.jpg
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The label is correct. The kit allows you to use a fired cartridge to gauge chamber headspace.:p;)


Cdoc42,

I think Hornady expanded the line. The way Stoney Point did it was they made both blank inserts available for turning on a lathe or, being a small company, would make you a custom size for a fee. They also offered the service of drilling out and threading one of your rifle's fired cases to become a custom gauge adapter for your chamber. I believe Hornady still offers that latter service, but don't know if the pandemic crunch has interfered as it has with a lot of custom work. Incidentally, I also don't know if Hornady actually makes the tool or if Stoney Point still makes them for Hornady on an OEM basis.

For bullet inserts, I've pretty much switched to the Sinclair inserts, which are made to mimic a throat shape better than the aluminum Hornady inserts do. They contact the bullet further down at or close to where it bullet will actually engage the rifling. In using both on the same bullets, I've measured slightly lower variation in readings with the Sinclair. Mind you, the extreme spread in the difference is only a couple of thousandths, which is no big deal if you aren't trying for a super-small bullet jump, but the shape does seem to make it easier to center the bullet and get a repeatable reading.
 
I have always heard that if you are bumping the shoulder .001 to .002 is about where you want to be.

With that said that was always in relations to precision bolt guns.

For my AR's reloading I bought a LE Wilson headspace gauge. I know I can measure the shoulder, but I just resize until it hits the MIN line on the gauge with the RCBS small base dies.

I know this is not ideal for accuracy. However seeing as my brass and ammo sometimes goes through several different guns my goal is reliability and to be similar to really good factory ammo. Consistently sized brass, consistent powder charges. small SD and ES
 
For me it is a simple matter. I set the head space on my rifles when I replace the barrels using a GO gage and then shim it with masking tape to use as a NO GO gage. When setting up my dies I simply use the comparator and the GO gage. That way I get a .002 - .003 shoulder setback. I get well into the teens on my brass and primer pockets always give out first. Pretty sure you could do the same with a factory rifle using a GO gage shimmed with masking tape to find your chamber depth.
 
I suppose its pointless now to mention that headspace is the measurement of the gun, not the case...

Early metallic cartridges had rims. Headspace was the measurement of the space in the barrel where the case head, including the rim had to fit. Still is with rimmed cases.

With rimless cases, headspace is the distance in the gun from the boltface to what ever point in the chamber stops the case. Can be a datum point on the shoulder, or could be the "ledge" at the chamber mouth used for straight (shoulderless) cases.

It always amazes me that the precision used for measuring guns and ammo isn't as rigidly adhered to when it comes to using the terms for those measurements...
A minor point it seems...but a valid one, I think.
 
I suppose its pointless now to mention that headspace is the measurement of the gun, not the case..
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Purely technically that is true and if we were making barrels and putting them on guns that has relevance (like Houndawg I do so and use his same method)

Realistically a fired case is an ugly form of headspace gauge.

You can't separate the two as they are both involved in the equation.

After all, what is head space for? Yep, its to accept a case that has been sized to and X standard.

A car without tires is not a functional car. A gun without a cartridge is a decoration.

Tech Head space exists for the purpose of accepting a cartridge that fires reliably.

Headspace does not exist in a vacuum (granted some people do have vacumous space in their head)
 
A car without tires is not a functional car. A gun without a cartridge is a decoration.
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Not if you live in a state that the ninth circuit court of appeals has jurisdiction over . . They have concluded that a firearm with ammo close by meaning not in the gun or magazine not in the gun . That still constitutes a functioning firearm . It’s is/was the rationale for and how we got for a short time unloaded open carry here in CA . It is also how some anti-gun states plan to force gun owners to keep their guns and ammo separate in the home because the precedent has been set that a unloaded firearm is just as functional as a loaded firearm for self defense.

EDIT

OP said:
Setting Headspace. Questions?
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Lets expand on the idea that the question was improperly asked in the title . What would be a better way to ask it while keeping it simple ?

Maybe

"Setting head clearance question ? "

" How to size a case for proper head clearance ? "

" How do I find and achieve proper head clearance "

" What the hell is head clearance " :D

How would you/we want the question we all know is being asked - asked ?

I ask because as RC20 rightly points even the CBTD measurement has no relevance without a specific headspace measurement to compare it to . When you use the term head clearance it incorporates both the CBTD and the rifles headspace measurements so you can come up with the proper head clearance when sizing your case ???
 
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Not if you live in a state that the ninth circuit court of appeals has jurisdiction over . .
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Let me re-phrase that, how about a car without an engine? Hopefully this does not get into an EPA issue (grin). Or our solar system without planets (and us and no head-space (pun) either.

The point is they are so interrelated as to become realist synonymous.

As has been noted, measuring a case is only relevant to that chamber and tool. I have two 270 inserts that disagree by a LOT.

Basics of finding the lands, moving back using the same tool holds for that person and his setup.

The concept is the same, specifics situation varies.

I do like to get Ogive from reloaders as it lets me know what ball park I am in.

My 6.5 x 47 specs out lower than listed but I have found ref to others that have an Ogive reading in the same area with the same mfg and model of bullet.
 
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