Headspacing issue with 5.56 and Redding National Match dies

[cwsanfor]

I am about to load my first 5.56 rounds and have a case headspacing question.

The cases are from LC M885 fired once in my SIG556. The equipment includes a Lee Turret (Hornady LNL AP and Lee Classic SS available but not being used), Redding National Match Die Set, Hornady Comparator, Giraud Trimmer, and L. E. Wilson case gauge.

I deprimed and tumbled the brass, swaged it in a Dillon D-600 SuperSwage, debarred and uniformed the flash holes and primer pockets, lubed with Imperial Sixing Wax, and sized in the Redding die, measuring the before and after comparator lengths of each case (see ). I then trimmed each case to 1.7523 in the Giraud.

I had previously set up the die to touch the shell plate, then about 1/8th further turn down. The press deflects slightly when I pull the lever, so I have some cam over.

I measured each of 107 cases with the Hornady Comparator, and got an average of 0.0029" shoulder pushback using the Redding Competition Shell Holder (0.006""). Thought I was GTG. Then I got an L. E. Wilson Gauge and all of the case bases I checked protrude slightly (about a rim's width) above the high step of the gauge.

At this point I figure the SIG556 must have larger than usual chamber headspace, and that I need more than .003" shoulder pushback to be within SAAMI spec, so I take some previously sized brass, put in the Redding Shell Holders 004", 002" and the standard Lee shell holder, increasing the shoulder pushback with each one. None of these resizings caused the case to properly fit the Wilson gauge: it seems I still did not push the shoulders back enough to be within SAAMI standards.

Not sure where to go from here. Options that come to mind include:

1) Lower the Redding sizing die, then see if case sized it it will clear the case gauge,

2) Try the Lee Dies until I can figure out how to set the Reddings,

3) Ignore the case gauge, load and fire these rounds and see what happens,

4) Ignore the SAAMI spec and assume the SIG556 has a very long headspace (same as 3),

5) Something else.

Thanks in advance.

Edited July 26, 2012 by cwsanfor

[DyNo!]

I cut the bottom of my dies to make them shorter and to allow deeper adjustment.

Although headspacing IS important, you probably won't die if it's just a little over.

I segregate into three batches during my final case gage check.

Ready to Shoot

Practice Ammo (Slightly over headspace specs go here and I shoot them all first. I've never had an issue.)

Dangerous/Pull

Edited July 26, 2012 by DyNo!

[Powder Finger]

What tool was used to measure the cases?

Did you make sure to remove the primer before initial measurement?

[cwsanfor]

What tool was used to measure the cases?

Did you make sure to remove the primer before initial measurement?

To measure the cases I used the Hornady Comparator with 330 insert, anvil base, and a Mitutoyo 500-195-20 Digimatic micrometer.

Yes, the cases were deprimed, tumbled in a stainless steel pin tumbler, swaged, flash hole deburred and uniformed, and lubed with a very light application of Redding/Imperial Sizing Die Wax before sizing.

[Graham Smith]

I may be completely off base here, but I think you're making this too complicated.

Everything you are using is for .223 which has a lot tighter tolerances than the 5.56 chamber on your rifle. I think that you are trying to take cases that have been fired formed to your 5.56 and trying to fit them back down to .223 specs. If the cases fit in a .223 gage, they will fit in your 5.56 with some room to spare.

[cwsanfor]

I may be completely off base here, but I think you're making this too complicated.

Everything you are using is for .223 which has a lot tighter tolerances than the 5.56 chamber on your rifle. I think that you are trying to take cases that have been fired formed to your 5.56 and trying to fit them back down to .223 specs. If the cases fit in a .223 gage, they will fit in your 5.56 with some room to spare.

I am sure you are correct. It's just that moving from straight-walled pistol loading to rifles and considering 60,000 psi going off a few inches from my nose makes me very attentive, and I'm trying to do this correctly at the beginning so I can build from there. Based on what I'm hearing at this and several other fora, I also agree with you that I am doing .223 things to a 5.56, and also mixing tools, like the Hornady Comparator and the Wilson case gauge. I think such tool mixing will yield what appear at first glance to be anomalies. I'm going to see if this brass chambers, then load a few, see if they magazine, chamber, and eject, check for setback, and light them up Saturday.

[justmike]

After cleaning and depriming I measure a fired case from MY AR then full length size till the shoulder is pushed back .004". Then trim to 1.750".

[Graham Smith]

I'm going to see if this brass chambers, then load a few, see if they magazine, chamber, and eject, check for setback, and light them up Saturday.

The most helpful thing I did when I was starting to load rifle was to make up a bunch of dummy rounds. No primers, no powder. You can mark the cases in critical points with a magic marker and see if some point on the case or bullet is rubbing.

[Old3GNR]

I use a JP case gauge. If it fits, its good and I use standard Redding dies. No bad things happened with over 10,000 rounds loaded except for the occasional primer falling out during firing. I use a hand tool for priming, if it seats too easy, discard the brass. Don't over think this. One issue I've had is the bullet sticking in the throat. I use copper solvent regularly in this area.

[cwsanfor]

Thanks, gentlemen, for your feedback. The bolt closed, and all ten test rounds fired without a problem. After firing, the shoulders were pushed out an average of 0.0012", so my die setting of 0.0029" shoulder setback seems appropriate. I suppose I could reduce it a hair, but this seems fine for now.

I am not sure the Wilson Gauge is useful to me since I an not loading to my particular barrel, not to .223 Remington SAAMI standards, so it goes back to Midway, and I'll continue with the Hornady Comparator.

[bgary]

I am not sure the Wilson Gauge is useful to me since I an not loading to my particular barrel, not to .223 Remington SAAMI standards, so it goes back to Midway, and I'll continue with the Hornady Comparator.

No, you still want to have a case-gauge. The comparator only tells you lengths... a case-gauge tells you whether your cases are within spec at mouth, shoulder, datum, body and rim. There are *lots* of ways a round can pass a comparator test, and fail to fit a case-gauge.

$.02

[cwsanfor]

I am not sure the Wilson Gauge is useful to me since I an not loading to my particular barrel, not to .223 Remington SAAMI standards, so it goes back to Midway, and I'll continue with the Hornady Comparator.

No, you still want to have a case-gauge. The comparator only tells you lengths... a case-gauge tells you whether your cases are within spec at mouth, shoulder, datum, body and rim. There are *lots* of ways a round can pass a comparator test, and fail to fit a case-gauge.

$.02

Interesting. I still am not sure what causes this round to protrude above the top step of the Wilson gauge. Should I try a Dillon gauge, or some other brand, or one that is 5.56 rather than .223? I think this round is correct for this gun, but I can't see the value of using a gauge that says it is not. Am I making any sense?

[bgary]

I still am not sure what causes this round to protrude above the top step of the Wilson gauge. Should I try a Dillon gauge, or some other brand, or one that is 5.56 rather than .223? I think this round is correct for this gun, but I can't see the value of using a gauge that says it is not. Am I making any sense?

First, understand that the difference(s) between 5.56 and .223-Rem are not about the external case dimensions. For all practical purposes, the cases are identical.

The relevant differences are in the *chamber* of the rifle the round is being fired through, and in the pressure rating of the ammunition. A .223 chamber has less freebore length (leade) and a sharper throat angle. A 5.56 round is rated for 20% higher pressure (60k CUP vs 50k CUP). The combination of these means that a 5.56 round fired in a .223 chamber may produce over-pressure... NOT because the case is different, but because the chamber is different.

With that knowledge, case-prep for 5.56 and 2.23 is effectively identical. And case-gauges are effectively identical (I don't even know that Wilson makes a 5.56-specific gauge, I'd be very surprised).

What the gauge does for you is tell you whether the relevant relationships (base-to-datum and datum-to-casemouth) are right. The "datum" (an imaginary point on the shoulder) determines both how far the cartridge can go into the chamber (affecting things like bullet-jump), and it affects how much headspace there will be between a chambered round and the closed bolt. You can "check" the location of the datam with a comparator, but a case-gauge tells you, at a glance, whether all the relationships are right.

Starting with sizing

-- a case on which the case-head sticks out past the upper shelf needs to have the shoulder pushed back.

-- a case on which the case-head drops in past the lower shelf has been over-sized (too much headspace)

AFTER sizing appropriately,

-- a case on which the case-MOUTH sticks out past the upper shelf needs to be trimmed (over-length)

And, if a case won't drop into the gauge cleanly, it should be tossed (or reprocessed). Either it is out of round, or the web is stretched, or the rim is deformed, or... in some other way, it is not ready to stick in a chamber. The ideal situation is that you drop a case into the gauge, it falls in with a "plonk", the case-head is just below the upper step at one end, the case-mouth is just below the upper step at the other end, and it falls out freely when you tip it out.

$.02

Oh, and BTW, unless you are trying to do long-range precision stuff (for which 5.56 isn't probably the right round anyway), don't sweat the 10-thousandths (0.000x"). Most of us measure to the nearest thousandth, and in practice plus-or-minus a couple of thousandths doesn't hurt anything. e.g., after sizing I trim cases to 1.752", but anything with +/- .003" of that is still well within the chamber spec.

[Religious Shooter]

Thanks, gentlemen, for your feedback. The bolt closed, and all ten test rounds fired without a problem. After firing, the shoulders were pushed out an average of 0.0012", so my die setting of 0.0029" shoulder setback seems appropriate. I suppose I could reduce it a hair, but this seems fine for now.

.0029-.0012= .0017" of set back for a semi-auto is on the edge of reliability. I'd personally push back the shoulders at least .003" back in a semi. So I would push it back to 0.004".

But experience is the best teacher. Load up and fire 100-200 rounds and see if that .0029 setting with the .0017" set back works for you. Maybe they will be 100%. Maybe they won't. I'd recommend that you see what that load does when the gun is hot and dirty.

[cwsanfor]

Thanks, gentlemen, for your feedback. The bolt closed, and all ten test rounds fired without a problem. After firing, the shoulders were pushed out an average of 0.0012", so my die setting of 0.0029" shoulder setback seems appropriate. I suppose I could reduce it a hair, but this seems fine for now.

.0029-.0012= .0017" of set back for a semi-auto is on the edge of reliability. I'd personally push back the shoulders at least .003" back in a semi. So I would push it back to 0.004".

But experience is the best teacher. Load up and fire 100-200 rounds and see if that .0029 setting with the .0017" set back works for you. Maybe they will be 100%. Maybe they won't. I'd recommend that you see what that load does when the gun is hot and dirty.

Religious Shooter,

We apparently share two interests .

Let be sure I understand you. For the first reloading of this LC M885 brass, my average shoulder setback was 0.0029". After firing, I measured the shoulder location again with the comparator, and found that the shoulder was advanced 0.0012" during firing.

I was thinking the 0.0029" setback was near the generous end of the 0.002-0.003" range I usually see cited for gas piston guns like this SIG556. Are you saying I should dial in a larger setback? Sorry for all the dumb questions, I am new at rifle loading.

[Religious Shooter]

IMHO it needs to be set back just a tad more.

When you see the recommended .002-.003" set-back range, that figure is applied to the fired brass from your gun. Not from SAAMI zero. Some gun's headspace may deviate from SAAMI due to use. That's why you need to set the headspace to the particular gun that you are shooting.

So take all the fired brass from you gun... measure them... then use that measurement as the "zero" and set-back the shoulder .002-.003".

But saying that your current setting may work. I use the RCBS MIC and for factory new ammo and I measured an average of:

Federal XM193 -2.3

American Eagle AE223 -1.9

Winchester Q3131A -1.4

Wolf 62 FMJ -4.5

PMC 55 FMJBT -2.9

Your setting of .0029" is the same as -2.9.

[cwsanfor]

IMHO it needs to be set back just a tad more.

When you see the recommended .002-.003" set-back range, that figure is applied to the fired brass from your gun. Not from SAAMI zero. Some gun's headspace may deviate from SAAMI due to use. That's why you need to set the headspace to the particular gun that you are shooting.

So take all the fired brass from you gun... measure them... then use that measurement as the "zero" and set-back the shoulder .002-.003".

But saying that your current setting may work. I use the RCBS MIC and for factory new ammo and I measured an average of:

Federal XM193 -2.3

American Eagle AE223 -1.9

Winchester Q3131A -1.4

Wolf 62 FMJ -4.5

PMC 55 FMJBT -2.9

Your setting of .0029" is the same as -2.9.

Got it. That's what I did, took the comparator measurement from the brass I just fired, and set the sizing die/shell holder to produce a 0.0026" shoulder setback from there, shown here.

[usmc0326]

I was thinking the 0.0029" setback was near the generous end of the 0.002-0.003" range I usually see cited for gas piston guns like this SIG556. Are you saying I should dial in a larger setback? Sorry for all the dumb questions, I am new at rifle loading.

So it sounds like you might need to check the case OAL after the cases get trimmed. After the cases get sized they need to be trimmed. That or your using standard dies when you may be needing to use small base dies. Take a cleaned deprimed/ sized case into the case gauge. Then trim it, recheck and do this throughout your loading process to figure out where the case is getting improperly sized. The M855 brass that I have used is very long after firing. I had to double check the saami spec for case length the first time I trimmed them because I thought they were way to short.

Edited August 22, 2012 by usmc0326