Longer headspace after resizing?

[gregj]

I recently starting reloading for my 223. Brass is PMC factory ammo that has been once fired in my AR. Dies are Hornady two die set. Press is LNL AP, but for sizing I use it like a single stage, only the resizing/decaping die is in it.

I have an RCBS Precision Mic, that I used to measure several once fired cases. Following the instructions, set up my die to bump the shoulder back .001-.002" from the fired case measurement. To achieve this the resizing die is screwed in about 1/4 turn more than where it just touches the shell plate when the ram is raised. Per Hornady, this is perfectly normal in order to do what I'm trying to do. The decapping pin is per spec, 3/16" below bottom of die.

My issue is if I measure several cases with the PM before and after resizing, the headspace seems to be quite a bit longer after resizing, additional .002 to .003", IIRC. I read somewhere if the plug on the decaping pin was too long into the case, it would tend to lengthen the case as it was pulled out. I made sure it was set per Hornady's spec, so I dont think that's the cause.

Could different consistencies in brass composition cause this?

 

[MtnCreek]

Are you talking about the overall length of the case increasing after sizing? If so, this is normal. .223 does not headspace off the case mouth. Do you have case trimming equipment? If not, you will likely find Lee's trimmer/case holder and a cordless drill make a good choice. Your reloading manual probably covers proper headspacing, you may want to re-read the first half of the manual (the part before the data).

 

[MEHavey]

For a gas gun, I would tend to ignore "fired-case" dimensions and do one of two things:

- Resize to SAAMI minimums each time, basing the measurement on the Prec Mic reading of a unfired commercial round.

- Strip the bolt of extractor/ejector and gradually increase the sizing bump on a case until the bolt just closes without feel. The PM measurement of that case is your new "headspace" zero. (I'd suggest doing this several times and taking the smallest number for headspace zero.) Adjust your sizing die to bump 0.002"+ beyond that.

 

[243winxb]

Shoulder & Neck move Forward on Full Length Sizing-Normal

My issue is if I measure several cases with the PM before and after resizing, the (Cartridge) headspace seems to be quite a bit longer after resizing, additional .002 to .003"

Its possible for the neck/shoulder to move back or become shorter on firing as the case body expands outward. When you FL size, the neck/shoulder moves forward again.

 

[USSR]

I have an RCBS Precision Mic, that I used to measure several once fired cases. Following the instructions, set up my die to bump the shoulder back .001-.002" from the fired case measurement. To achieve this the resizing die is screwed in about 1/4 turn more than where it just touches the shell plate when the ram is raised. Per Hornady, this is perfectly normal in order to do what I'm trying to do. The decapping pin is per spec, 3/16" below bottom of die.

My issue is if I measure several cases with the PM before and after resizing, the headspace seems to be quite a bit longer after resizing, additional .002 to .003", IIRC. I read somewhere if the plug on the decaping pin was too long into the case, it would tend to lengthen the case as it was pulled out. I made sure it was set per Hornady's spec, so I dont think that's the cause.

Case headspace is determined by how far your FL sizing die is screwed into your press. Forget the 1/4 turn "one size fits all" instructions. If you have too much headspace, you need to unscrew the die a bit more, and if you don't have enough headspace, then you need to screw the die in a bit more.

Don

 

[Walkalong]

Could different consistencies in brass composition cause this?

Absolutely. Soft brass will spring back less when the brass is pulled out of the sizer. Work hardened brass will spring back a good bit. Easily .003 difference.

I size .223 brass to fit a Wilson gauge. There is a little leeway there. Some can be shorter than others and all still pass the gauge.

 

[brickeyee]

Did you lube the inside of the case neck?

It does not take much, but some needs to be there.

 

[MtnCreek]

My issue is if I measure several cases with the PM before and after resizing, the headspace seems to be quite a bit longer after resizing, additional .002 to .003", IIRC. I read somewhere if the plug on the decaping pin was too long into the case, it would tend to lengthen the case as it was pulled out. I made sure it was set per Hornady's spec, so I dont think that's the cause.

Unless I'm reading this wrong, I think gregj is talking about case length, not headspace.

 

[USSR]

Unless I'm reading this wrong, I think gregj is talking about case length, not headspace.

He's measuring with the RCBS Precision Mic, which measures case headspace.

Don

 

[MtnCreek]

He's measuring with the RCBS Precision Mic, which measures case headspace.

Don

Roger That! I'm Wrong!

 

[ranger335v]

"He's measuring with the RCBS Precision Mic, which measures case headspace."

Just as a techical matter in a technical activity, cases don't have "headspace". The Mic (and the other simular function tools) measures head-to-shoulder length and that's all. And it typically measures about 3 thou variation in the same box, both when fired and resized. Headspace is only in the chamber and it doesn't vary at all.

 

[USSR]

ranger,

Tell that to Sinclair and some of the other retailers of precision reloading equipment who list case/cartridge headspace tools. While you are technically correct, chamber headspace is based on the assumption that the ammo being fed into the chamber is factory ammo with the SAAMI dimensions that manufacturers follow. Once guys start resizing brass to various dimensions, headspace changes can be induced by the varying case dimensions. After all, to paraphrase Boots Obermeyer: headspace is essentially the relationship between the case dimensions and the chamber dimensions.

Don

 

[gamestalker]

Headspace is a measurement of the space between the case head and the bolt face, and with a .223 case it is controlled at the shoulder. If your necking your brass rather than FL sizing headspace becomes less an issue with more than once fired brass, but still a critical area of functional firearm physics.

 

[Sport45]

Did you lube the inside of the case neck?

It does not take much, but some needs to be there.

This^^

As the expanding button is being pulled back up through the neck it is stretching the case.

 

[USSR]

Headspace is a measurement of the space between the case head and the bolt face...

No, headspace with bottlenecked, nonbelted cartridges is defined as the distance between the bolt face and the datum point of the shoulder. Chamber headspace guages measure that, not the distance between the case head and the bolt face. Having the correct amount of space between the case head and bolt face is the end result, but it is not defined or measured as the head space measurement.

Don

 

[Walkalong]

headspace is essentially the relationship between the case dimensions and the chamber dimensions.

Having the correct amount of space between the case head and bolt face is the end result, but it is not defined or measured as the head space measurement

Yep


"Headspace" discussions always tie folks up in knots.

I like to refer to "mechanical" headspace, which is what is machined into the chamber. (As Don aptly described)

I also like to refer to "working" headspace, which is the actual amount of wiggle room the case has after sizing and chambering in any one chamber.

We can do nothing about the "mechanical" headspace since it is machined into the gun by the maker.

We can control "working" headspace using our press and sizer.

So, for me, headspace is fluid, despite the fact that technically headspace is a set figure (+ or - tolerances) machined in to the action/bolt relationship

AC

 

[MEHavey]

'Chamber' headspace & 'cartridge' headspace was all I ever needed to clarify the situation.

 

[ranger335v]

"ranger, Tell that to Sinclair and some of the other retailers of precision reloading equipment who list case/cartridge headspace tools."

I don't have to, they know it. But, the term "headspace" has gotten so muddled and misused it has virtually lost any real meaning and that's not helpful.

The actual meaning of headspace is the space for the chambered cartridge to fit, no matter how the chamber is cut. So, only manufactors and gunsmiths need be concerned about headspace, per se. Once the chamber is cut the headspace is fixed in time and space, unless it changes due to wear or abuse.

Reloaders such as Gregj have a whole different thing to deal with in cases, that's why he asked how to best use his Mic tool. Seems anytime headspace is mentioned someone will immediately leap in with verbal contortions to describe how and where it's measured, as if that has anything at all to do with what a reloader can or should do about it. Fact is, no matter what the "spec" is, the ONLY thing a reloader can do is stive to make HIS cases fit HIS chamber, no matter what the actual headspace is; that's one of the major advantages a reloader has over factory ammo.

Thus any mention of a "datum" line is not only useless, it actually clouds the issue and leaves the poor guy with no idea of what he should do about it! And what he should do, dear hearts, is to FL size all bottle neck cartridges from the head to the shoulder so his cases are a snug but not tight chamber fit; datums - and belts or rims - be damped.

 

[gregj]

Case headspace is determined by how far your FL sizing die is screwed into your press. Forget the 1/4 turn "one size fits all" instructions. If you have too much headspace, you need to unscrew the die a bit more, and if you don't have enough headspace, then you need to screw the die in a bit more.

This is exactly what I described as doing. The "one size fits all" instructions from Honady state to lock the die down when it touches the shell plate. I called Hornady's support folks, described what I was trying to do, and they recommended to screw the die down more, but to not go beyond 3/4 of a turn. The resulting 1/4 turn past shell plat/die meeting point, results in a fairly decent feeling camming over effect. Hornady support said this was normal, but they would machine off .005" off the bottom of the die if I wanted, as that should eliminate the camming over feeling.

No, headspace with bottlenecked, nonbelted cartridges is defined as the distance between the bolt face and the datum point of the shoulder. Chamber headspace guages measure that, not the distance between the case head and the bolt face. Having the correct amount of space between the case head and bolt face is the end result, but it is not defined or measured as the head space measurement.

Sorry, not been around to clear up any confusion from my post. Yes, this exactly what I am measuring. I am useing FL Hornady sizing die. All my research indicated for gas guns, fired cases should be bumped back a small amount to minimized the working of the brass, which not only affords a better chamber fit for MY gun (rather than just sizing to SAAMI spec), and should make the brass last longer. This is what I'm trying to do.

Did you lube the inside of the case neck?

It does not take much, but some needs to be there.

Indirectly, yes, as I put Imperial sizing wax on my hands and lube each case. I can visably see excess lub on the mouth of each case. But I have not taken a lube brush to each case. I did try spraying the case mouths with Hornady One Shot, and that did not seem to have any effect. I will try the lube brush and more closely monitor the results next time.

 

[gregj]

Ranger:

Fact is, no matter what the "spec" is, the ONLY thing a reloader can do is stive to make HIS cases fit HIS chamber, no matter what the actual headspace is; that's one of the major advantages a reloader has over factory ammo.

This is exactly what I am trying to accomplish, using tools that my research pointed me to as being adequate for the task at hand.

Thus any mention of a "datum" line is not only useless, it actually clouds the issue and leaves the poor guy with no idea of what he should do about it! And what he should do, dear hearts, is to FL size all bottle neck cartridges from the head to the shoulder so his cases are a snug but not tight chamber fit; datums - and belts or rims - be damped.

Ok now, I' not that much of a noob! I work in IT, so I am technically savvy, as well as mechanically inclined. I've not been reloading as long as others here, but long enough to know which end the bullit goes into. I didnt want to get into a mags vs clips view of what I posted, so I do strive to use the correct terms, and those that are used by my various tools (the RCBS PM instructions (which BTW suxs rocks)), and my manuals. But I'm always learning something new here.

Thanks for all the input.

 

[Walkalong]

'Chamber' headspace & 'cartridge' headspace was all I ever needed to clarify the situation.

I like that. One being static (machined into the gun and, as ranger335v posted, "fixed in time and space, unless it changes due to wear or abuse.), and the other being fluid. (The case's relationship to the chamber, or how much we push the shoulder here or there.)

I am only interested in "working" headspace, as I defined it earlier, whether technically correct or not. That is what can get us into trouble, or keep us out of trouble.

Sounds like gregj gets it, so it's all good.

 

[ranger335v]

"Ok now, I' not that much of a noob! I work in IT, so I am technically savvy, as well as mechanically inclined. I've not been reloading as long as others here, but long enough to know which end the bullit goes into."

Well, okay, all youse guys look the same on the web. Anyway, it wasn't a shot AT you, just a broad observation for whatever it's worth to anyone following the thread. Web debates on "headspace" descend into deeper holes than 'magazines' vs. 'clips' and the less some know about the meaning of either, the deeper & louder the hole gets!

Good luck!