Measuring headspace

General Firearms Reloading & Ammunition
1

I’m brand new to reloading, with the goal of making precision reloads 223 for my mk-12ish rifle. I’ve finished reading the ABC’s of reloading and have purchased a press, some dies, caliper and a few other things. Not quite enough equipment to start reloading.

I purchased a Hornady lock-n-load headspace comparator. It is the type that clamps onto a caliper on one of the jaws. Tonight I was setting up my Redding type S full length die, and I’ve been having difficulty getting precise measurements of headspace. Depending on how I hold the casing the numbers fluctuate by 1-2 thousandth, and there is a bit of fiddling to find the lowest value.

What method or tool do you use? I’m hoping there is a faster and more accurate tool.

Thanks for helping a noob.

2

The hornady tool works well, you need to rotate the case in the comparator to try and “square it up” in the comparator.

When I am setting up a die like you are, I will fire the case, neck size it only, reload it, then fire it again. This is the same process that I and others use when having custom dies made as well. The second firing will give you a truer read on your chamber dimensions. That said, you do not have to do this.

Simply use the lowest value reading you are getting from the comparator, then slowly adjust your seating die until you get the desired amount of shoulder bump. I have always been a huge believer in using shims with my seating dies to control shoulder bump (head space). Say you want a .003 bump, adjust your die, lock it down, only to find that somewhere along the line you ended up at .005? Just stick a .002 shim under it!

http://www.sinclairintl.com/reloading-equipment/reloading-dies/replacement-parts-amp-upgrades/skip-s-die-shim-kit-7-8-14--prod33197.aspx

EDIT: since you are loading for your mk-12 don’t take my advice on neck sizing then firing again, you need to FL size, my apologies, was thinking bolt gun

3

Do you have the expander ball still in the die? When you size the brass, the expander ball tends to stretch the shoulder a bit when sizing the neck on the upstroke of the press. However, when using the Hornady comparator, you do need to wiggle the case around to find a true reading. I usually measure the first 10 or so, then keep moving. I may measure 1 in 20 after that.

With that, .001-.002 is nothing for an auto-loader… it’s consistent enough.

4

Just squeezing hard on the calipers can cause a 0.001" variation in readings, The jaw can flex. The best Brown & Sharpe $200 calipers flex up to .0005", how much a $30 set of calipers flex, who knows.

5

I simply use a case gauge and take the average of at least 5 pieces. Brass with have different spring back so a few thousandths variation is totally normal. Plus, as OnyxZ mentioned, the expander ball pulling out will create all kinds of badness.

I took my expander ball out and went with a separate neck expander die. It’s an additional step, but you get less case trimming since it sizes on the down stroke. I think you get less neck runout too, but I never measured to confirm.

6

Thanks for the info everybody. It is really appreciated. It seems I have adequate tooling, I only need to get more practice taking measurements. I looked up wilson case gauge and watched a video. I might pick one up sometime as it gives a quick visual on where you are in relation to SAAMI specs.

I sized a few cases last night with and without the expander ball. I’ve read a few threads about people listing the problems with the expander. I will be looking into this next a little more carefully.

Masan - Thanks for the link. I didn’t know these existed and might be useful. I actually have a set of the redding competition shellholders. Last night when I wanted less shoulder bump, I just switched the shellholder out to a different size. It seemed to work.

Markm - I could FL resize without the expander ball, and then insert the expander ball to resize the neck on the down stroke, however I would only move the press enough to run the expander ball through the neck, and not enough to FL resize a second time. Would this work or is that bad? Alternatively, if I choose the correct bushing, do I need to expand the neck at all? I’m on a single stage press.

Thanks everyone! I will post pics sometime soon. I’m itching to get into this long range business and getting excited.

7

I’d spring for a neck expander die and a LNL conversion kit. This way you can jump back and forth between dies in 2 seconds. Your way might work, but it’s a bit of a pain to reassemble the die every time.

I personally hate bushing dies. I’ve messed with them quite a bit on .308, and hate them. Not sure about .223, but in .308 you have to have a bushing for each kind of brass. Thin necks won’t size the same as thicker because you’re working off the outer diameter. Example… If you set up the die/bushing to work with Lapua, if you switch to WIN/Hornady thin neck brass, the bullet just drops into the case. Plus you get the dreaded donut issue. And I could never get consistent neck straightness no matter what. I tried floating the bushing, tightening it etc. Complete pain in the ass.

8

P2000

Buy a Forster .223 full length resizing die, the Forster die produces the least amount of neck runout when sizing.

Below I ordered the Forster spindle and expander assembly for my RCBS .223 dies.

The Forster spindle and expander “float” and self center in the case neck, under the spindle lock nut is a thick rubber washer which allows the spindle to move. The case neck is still inside the neck of the die when the expander enters the case neck. This centers the expander with the neck of the die and the expander can not be pulled off center and increase neck runout. You will need to lube the inside of the case necks with graphite or regular case lube and the necks will not stretch.

With the Hornady cartridge headspace gauge all you need to do is spin the case while you close the jaws of the vernier calipers. This centers the case in the in the bottom jaw of the calipers for uniform readings.

Below measuring a new unfired Federal M193 cartridge.

Below a Colt 5.56 Field headspace gauge 1.4736

And below is the Field gauge in my “calibrated” Hornady Headspace Gauge.

To calibrate the gauge all I had to do was loosen the set screw between the silver and red halves of the Hornady gauge and insert a .011 feeler gauge and tighten the set screw. Meaning the gauge was reading .011 short so I opened the gap between the two parts .011 and now the gauge reads exact headspace.

Below a fired unresized case in the gauge.

Below the same case after full length resizing with .003 shoulder bump.

I do not use the shims under the dies lockring, I use Redding competition shell holders, this allows me to adjust the cartridge headspace or shoulder bump by just changing the shell holder and not touch the die.

Below on the right is a standard RCBS shell holder and on the left is a competition shell holder that is .004 taller than the RCBS shell holder. Meaning .004 “less” shoulder bump, there are five shell holders in this set and each one is .002 taller than the next one. This allows me to have the press cam over for more uniform case headspace lengths when sizing and also removes any slop from the press.

My Wilson case gauges are semiretired and I use my Hornady gauge for most of my case measuring needs.

9

The redding competition shellholders accomplish the same thing as shims. Good piece of kit, but cost more $ and not as versatile (.308 shellholder doesn’t help with .223 for example). I think the OP said he had these, so no reason to purchase shims. I usually offer the shim idea because it is so inexpensive and versatile.

Also OP, if you try your method of reinserting the xpander ball, watch how much the decapping pin rotates (wobbles) as you screw the stem in and out, you will see why we chuck those things in the scrap pile. Bigedp51 mentions a good alternative, the floated stem from the forster die. Basically, you would need to decide if you want another sizing die that still expands the neck on the upstroke (more trimming) or an expander mandrel die that sizes the neck on the downstroke (less trimming). Either choice is a good one, the forster die is a one step process, the way markm and I do it is two step.

Don’t worry about SAAMI specs too much, instead focus on what your fired brass is telling you. Good Luck!

10

masan

I have a set of the shims and they do not do the same thing as the Redding competition shell holders. When you use the shims you raise the die away from the shell holder. When the die makes hard contact with the shell holder (press cam over) all the slop and play is removed from the sizing operation. Meaning the press is removed from the sizing equation and the case shoulder to base measurement is more constant with less brass springback. (Case headspace length)

I still use the Rockchucker press I bought in 1973 and presses will have slop depending on their age or the quality of the press. Again I have and used the shims but stop using them in favor of the competition shell holders. Another advantage of the competition shell holders is once the die is set up and producing sized cases with minimum runout the die does not have to be moved or touched to adjust shoulder bump.

I also have the Sinclair expander die and mandrels and the mandrel “floats” inside the die and can increase neck runout depending on neck uniformity. The Forster die supports the case neck on the down stroke of the ram and the case neck stays aligned and centered with the neck of the die. Meaning no induced runout from the expander and straighter cases in “one” single operation. The Lyman type M die is optional depending on your seating die in a aid to start the bullet straighter in the case neck if seating increases neck runout.

Bottom line, the Forster full length die will produce the least amount of runout without turning the case necks, and if you turn the necks it will be even less.

11

When I said that the shims accomplish the same thing I was referring to adjusting shoulder bump.

As for cam over removing all play from the resizing process, you are correct in that the shell holder contacting the die removes any chance that the die will move away from the ram as the press itself stretches as the brass is sized because the brass is no longer pushing up on the die, the ram/shell holder is.

I believe that cam over is absolutely needed if you are forming brass into a new cartridge or if you are sizing for a semi automatic that is especially hard on brass (m14 for example).

I have never experienced head space variences beyond half a thou on brass that I have FL sized in a die set up with a shim, be it from a bolt gun or an AR. A 3 thousandths shim is less play than you will find between the case and shell holder (I can get a 7 thou feeler gauge between my no.3 shell holder and a piece of Lapua .243 brass). This is on a Redding T7.

A quote from Sierra about squaring dies (something vital for all reloading dies): “Due to the many calls and letters regarding the accuracy tip “Squaring Your Dies” in the last issue of “The X-RING”, a bit of explanation is required. As pointed out by our callers, often times a properly adjusted die will not touch the shell holder, even when full-length resizing. In these cases, a machined spacer some .040” to .050" thick (like a flat washer) placed between the die and shell holder will allow you to apply pressure to the bottom of the die."

Link to the quote from Sierra : http://www.sierrabullets.com/resources/x-ring-newsletter/index.cfm/xid/2/Accuracy-Loading-Tip-Squaring-Your-Dies-cont/#loadtip

The spacer mentioned is for squaring the die to the press/ram. As for the part about “often times a properly adjusted die will not touch the shell holder” seems to make my point.

As for runout, what is the difference between the Forster spindle floating on a rubber washer and the sinclair mandrel floating on a rubber o-ring?

I ran 100 pieces of virgin Lapua 6BR brass over a .243 mandrel last night, because virgin Lapua brass has super tight necks. I loaded that brass this morning. My sinclair gauge is showing >.001 runout measured below the ogive. Granted, using my hand seater and arbor press will eliminate nearly all runout on its own, but if the mandrel had been imparting any runout on the case necks then there should be some indication of it in the loaded ammunition.

OP, like I said before, the Redding shell holders or the shims will allow you to adjust your shoulder bump (head space) and since you have the Reddings you are golden. You can accomplish the same thing with the lock ring on your sizing die, just takes some patience and trial/error. In regards to needing to expand the neck, standard FL sizing dies size the neck small, so that when you pull the expander ball out of the case the neck gets sized to the proper dimensions. So, if you remove the expander ball from your current FL sizing die you will need some way to expand the necks to the proper dimension. Neck busing dies allow you to control the amount of neck tension you have but work best if used with neck turned brass. Like markm said, they suck for mixed brass and are ho hum for unturned necks. The forster spindle will work well for you, as will the sinclair, though I would definitely try using your Redding Type S FL sizing die as is, with the expander ball in it. The type S dies are very well made. As Onyxz said, 1-2 thou is acceptable to brass coming out of an auto, they are much harder on brass that a bolt gun.

12

In the Forster die the case neck is still centered inside the neck of the die and supported when the expander enters the case neck. Meaning the Forster expander can not pull the necks off center during the down stroke of the ram.

The Sinclair mandrel floats and is not self centering (even though they say it is) and is not supporting the case neck, on top of this it was designed for opening up the necks before turning. And this is why you have two mandrel sizes, one to expand the case neck and a smaller one to turn the case necks on.

So again the mandrel floats in the expander die, the case floats in the shell holder and the case neck is not supported. If the case necks are not turned the thin side of the neck will expand more and induce “MORE” neck runout.

The expander die is used on new cases to uniform the necks before fire forming because they do not want to go to the trouble of lubing the case and full length resize these new cases. If a full length die was used the entire case is supported and aligned inside the die. If you measure neck runout using a full length die with the expander removed the case will have near zero runout. It is the act of expanding the case necks and seating bullets that induces and increases neck runout

Complete Precision Case Prep
Preparing Cases for Long-Range Accuracy
http://www.accurateshooter.com/technical-articles/reloading/complete-precision-case-prep/

If you notice below my RCBS die has a Lee lock ring with its rubber o-ring, this allows the die to float and self center in the press threads. This turns my 42 year old Rockchucker press into a Forster Co-Ax press for a fraction of the cost.

O-Rings on Dies May Reduce Run-Out
http://www.accurateshooter.com/technical-articles/reloading/o-rings-on-dies-may-reduce-run-out/

13

Thanks for all the info everyone. I’m trying to digest it all.

It seems I have 2 options, please correct me if I’m wrong on anything:

Option 1: Get a Forster FL resizing die.
Pros: 1 step solution
Cons: I have to lube the inside of necks. Neck sizes on the upstroke which may require more trimming

Option 2: Remove expander and bushing from my Type S FL die, and use it to bump shoulder. Then use a neck expander die (or Lee collet?) as a second step.
Pros: less trimming. No lube inside cases
Cons:2 step process

What about neck tension? I read that I don’t want to crimp my 77gr SMK’s, which was one reason I went for the Type S die with bushings. I realize some of you Dillon users do a light crimp, but I’d like to avoid crimping all together because that is another step on my single stage press.
I hear I can polish a neck expander or lee collet if needed to produce more neck tension. Can this be done with the Forster FL die as well?
Thank you!

14

P2000, I would suggest using your Redding Die as is first, see if the results it gives you are acceptable for you. If not, option 1 would likely be the easiest solution. You will be lubing the inside of your case necks regardless of what you do (short of turning necks and getting a custom FL die from Harrels or Whidden).

As for crimp, I ran 77 smk’s for a long time using a standard rcbs FL sizing die with the expander still in it, no crimp. That ammuntion would shoot under 0.25 MOA through this gun: https://www.m4carbine.net/showthread.php?135825-Not-my-first-build-but-likely-my-best

Some guys here do run a light crimp on their SMKs, and I think that the light crimp gives them a more consistent neck tension that ultimately outweighs any deformation to bullet.

Again, try what you have before you spend more $. As you can see, there are a lot of different approaches to the same goal. What works best for some may not work as well for others.

All of this talk about runout, neck tension, and things like neck turning, bullet sorting, meplat trimming and pointing that you may read about are all geared towards squeezing out every last little bit of potential accuracy. With a basic FL sizing die, a seating die, and the other basic components for handloading you can produce ammunition for your rifle that will surpass 99% of factory offerings (once you get the hang of things).

15

This is some good advice. Thanks. I will give my Type S a try and then go from there. I will probably end up trying other methods discussed in this thread as well to see where I end up.

In regards to lubing necks, I was thinking that with the Lee Collet die it is not needed. That appeals to me. I’d rather set up an extra die than have to lube 100 necks and get that dry lube powder stuff everywhere.

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16

P2000

You have a AR15 rifle with a chamber .002 larger in diameter than a standard SAAMI .223 chamber and its not a bench rest rifle. You also have a bushing die designed to resize cases with turned necks, and without turning the neck all your doing is pushing the neck defects to the inside of the neck. A bushing die should not size a case neck down more than .005 small than its fired expanded size or you will induce neck runout. And if you are not turning the necks of your cases you have the wrong type die so I have a few questions.

  1. Do you have a neck thickness gauge?
  2. Do you have a runout gauge?
  3. What made you buy a bushing die for a AR15 rifle?
  4. Do you have a tight custom chambered AR15 rifle?

Two-Step Sizing and Case Neck Concentricity
by: Germán A. Salazar
http://riflemansjournal.blogspot.com/2010/04/reloading-two-step-sizing-and.html

“This article’s title refers to two-step sizing, a term that may not be familiar to all, so an explanation is in order. When sizing with bushing dies, such as the Redding Competition and Type S dies, it is well known that a neck diameter reduction of more than 0.005” should be accomplished in two steps, with each step sizing the neck down no more than 0.005" and preferably less (see October 2009 article about neck tension). This two-step procedure not only minimizes sizing die induced concentricity deterioration, but it also yields a finished neck diameter equivalent to the bushing’s nominal size. It is often found that when using a single bushing to size more than 0.005", the finished neck diameter is smaller than the bushing’s nominal size. Those are the basic reasons for two-step sizing."

Bottom line, you need a one piece full length die and not a bushing die, and in my opinion the best die would be the Forster die with the high mounted expander.

Also your cases get longer when resizing because the brass has nowhere else to go but up and into the neck when full length resized and very little of the neck length increase is due to the expander button.

I have eight different .223/5.56 dies and I can tell you the best and simplest die for your AR15 is the Forster die or a die equipped with the Forster spindle and expander unit. And if you do not have a custom tight neck chamber you need a bushing die like you need another hole in your head. Too much of what the benchrest shooters do has filtered down to people with standard off the shelf factory rifles. And if you do not have a custom chambered rifle you are wasting your time and money buying equipment trying to make it shoot like one.

17

Anyone who tells you with absolute certainty TO or NOT TO crimp is an imbecile. People do it both ways with great success.

If you don’t want to crimp, you probably need to anneal to get consistent neck tension. Sinister, here, found that annealing was the most critical factor in accuracy in his process where he didn’t crimp.

Annealing, in my opinion is a much bigger ass ache than crimping… however, I do anneal and skip the crimp for .308 and 300 WM. .223 is way too much volume to be annealing for me.

18

Bigedp51,

Thanks for all the info and the article link. You have been very helpful. I didn’t realize these caveats to using the bushing die. I didn’t know about the donuts either.

Once they come off of backorder, I’m going to pick up a Forster die like you recommend. Knowing me, I will probably tinker around a bit as well. I’m learning here.
To answer your questions,

  1. Do you have a neck thickness gauge? No, and I don’t plan on turning necks either.
  2. Do you have a runout gauge? Not yet but I do plan on getting one eventually as a way of checking and improving my process.
  3. What made you buy a bushing die for a AR15 rifle? I should have done more asking around here first. I was trying to use a system which produced consistent and accurate neck tension.
  4. Do you have a tight custom chambered AR15 rifle? It’s a Centurion Mk12 barrel. I do know the headspacing is tighter than my SR-15 and BCM BFH. (I made some casings progressively smaller and smaller. One which will not chamber in the Mk-12 will drop into the SR-15 like a hotdog thrown down a hallway.

MarkM - that is good to know about annealing and neck tension. Sounds like a PITA. Thank you

19

P2000

If you full length resize a case with the spindle and expander removed the case will have its lowest runout readings. When you add the expander button and bullet seating to this the runout can increase.

Below is a full length resized Remington case using the dies expander and it has approximately .004 neck variance. This .004 will show up as neck runout if you check the case after sizing.

If you do not have a neck thickness gauge you will not know if the expander button is pulling the necks off center or if you have variances in neck thickness.

If the neck has this much thickness variations the case body will also and warp when fired because the case will expand on the thin side of the case more.

And even if you turn the neck of the case the bullet will not be aligned with the axis of the bore. A neck thickness gauge is a diagnostic tool even if you do not plan to turn the case necks.

The Military conceders anything with .003 or less runout as match grade ammo. And having gauges keeps you from scratching your head and asking why your group size is bigger and wondering if its you or your reloads.

Cases like the Remington above are shot out of my iron sighted AR15 carbine as blasting ammo. The better more uniform cases are fired in my AR15 A2 HBAR and .223 bolt action.

Below shooting zombies with low grade blasting ammo.

Below shooting zombies at 300 yards using your best reloads and scoring the most points.

And if you do not want to make the best possible accurate ammunition then you better make friends with the zombies.:wink:

Sorry, its Sunday night and “The Walking Dead” is on tonight.

20

Thanks again Bigedp51. Don’t give any spoilers on The Walking Dead. I have to wait for Netflix to see the episodes.

You have a fine collection of diagrams. These would have been helpful in my reloading book. Now I realize a neck thickness gage will be in my future.

For now, I’m content buying blasting ammo vs rolling my own. I’m only getting into this obsession for some more accurate loads. I’ve got a steel plate that I want to shoot at 600-1000 yards out in the desert. But I’m sure that someday I will be reloading all of my 223 ammo.