Headspace variations once fired FL sized brass.

[DenverDave]

I recently got a Hornady headspace gauge and measured the HS of about 40x pieces of once fired brass that's been FL sized.

Now I made a rookie mistake by not sorting the brass fired from 2 different rifles. Due to this I expected to see two distinct different HS measurements, one from each gun or due to the FL sizing the HS would be more than less the same. Instead my measurements range from 1.515 to 1.565. The most frequent measurements being 1.530 (16/50) and 1.515 (10/40) with the rest equity distributed between 1.535 and 1.550 except for a couple outliers measuring 1.560/65.

All the brass is once fired Hornady.

I am trying to make sense of these results, determine if I have my FL die set up wrong, and how to best use this brass (will the different HS effect accuracy?)

 

[Sheldon N]

Can you double check your measurements? Headspace should not be varying by that much... 1.515 to 1.565 is 50 thousandths difference. Your goal should be to have the sized brass be within 2 thousandths of the fired brass.

Are you transposing a decimal place?

Brass should be segregated between rifles, and it's quite possible that you'll need different die settings between rifles. Example: Gun A gives fired brass measuring 1.563, you adjust the die to size the brass to measure 1.561. Gun B gives sized brass that measures 1.559, you size brass to 1.557. Make sure to take all measurements with the primers removed, they will give you false readings.

 

[JCCinOhio]

I'm still an apprentice reloader at best, but two things I've noticed/deduced.. Experts please tell me if I ate too much lead paint..

1) Different pressures (I assume) from different loads (say 55gr vs 65gr) can cause the brass to not grow to it's full extent. To get good readings I measure cases that were near max with a heavy bullet. These are usually more consistent and give a better idea of what I feel is my true headspace.

2) Dirty cases and/or a dirty chamber can also cause cases to stick to the chamber when in a more fluid state. This will cause them to not grow as much as they would otherwise.

So, you may try working a load up to a decently hot round with a heavy bullet for that caliber, and making sure your ammo and chamber are clean.

 

[918v]

Use an inverted .40 S&W case instead of the problematic gauge to measure HS.

 

[GhengisAhn175]

If you're using a Hornady die did you lock spindle down hard or did it move?

did you clean your cases prior to sizing?

what lube did you use?

did you lube the inside of the neck?

what was chamber A's fired spec and what was chamber B's fired spec?

 

[elfster1234]

I keep brass with that one particular rifle... as the brass is fire formed for the rifle's particular headspace. do not mix up your brass with other rifles IMO... put the rifle the ammo is used for right on your info card...

as for getting a consistent bump on your brass #1. keep brass with that particular rifle #2. clean sizing dies after each use #3.) get an even coat of case lube on the brass... if you're not using imperial case wax = then you should.... ill put the smallest dab of wax in the palm of my hand, spray that hand with lube, spray down brass, then work the brass with that hand... don't over do the lube #4.) the key to consistent bumping of the brass is consistent pressure "of how you run your handle / ram"...

 

[DenverDave]

Thank you all for your advice. I went through the brass again and have determined that I had false reading due to the brass being primered (noob mistake). Cleaned/sized another batch of once fired cases and got far more consistent readings, within .002.

In doing some research on headspace I found a few sources that said the Hornady HS tool functions as a comparator not a gauge because it measures from a different datum line than the SAAMI specs. Can anyone speak to this?

 

[spife7980]

It's not an exact measurement of your chamber. If you could document where your datum line was so that it would be possible to others to repeat it then you would be a bit more exact. On top of that the brass expands to fill the chamber and at that point if it's what we mere measuring it would be exact, but the brass shrinks a little. So it's not an exact replica of the chamber. And also piece of equipment to piece of equipment you might not get the same measurement. Mine may read .491 and yours could read .492.

But it will give you a consistent reading and a constant for you to use in sizing your brass. So it's not real world exact but it is correct relative to what you are doing in your own personal particular situation.

 

[FLIGHT762]

Thank you all for your advice. I went through the brass again and have determined that I had false reading due to the brass being primered (noob mistake). Cleaned/sized another batch of once fired cases and got far more consistent readings, within .002.

In doing some research on headspace I found a few sources that said the Hornady HS tool functions as a comparator not a gauge because it measures from a different datum line than the SAAMI specs. Can anyone speak to this?

The reason it measures from a different datum is that there is a chamfer on the edge of the .400 insert. This chamfer can vary form .010"-.020". I have two .400" inserts. One measures 1.611" on a 1.630" Go gauge indicating it has a .019" chamfer. The other insert measures 1.622" on a 1.630" Go gauge indicating a .008" chamfer.

The Hornady tool is a comparator, not a true headspace gauge. You can measure your insert with a 1.630" Go gauge and see what it reads if you want to know what 1.630" SAAMI minimum measures.

It can be explained here. In the video, but be aware, he keeps saying hundredths when he means thousandths.

 

[elfster1234]

Thank you all for your advice. I went through the brass again and have determined that I had false reading due to the brass being primered (noob mistake). Cleaned/sized another batch of once fired cases and got far more consistent readings, within .002.

In doing some research on headspace I found a few sources that said the Hornady HS tool functions as a comparator not a gauge because it measures from a different datum line than the SAAMI specs. Can anyone speak to this?

They are not a true "headspace gauge " and are more of a "bump guage" that should only be used as a reference of how much you're bumping the shoulder of that brass back from fire formed brass.... make note that even if your friend owns the very same tools and measures one of your pieces of fireformed brass that his measurement will most likely be a tad bit different (but close).... all the tool is doing is showing you when sizing the brass that you have actually moved the shoulder or not... super important to decap all your brass for potential cratered primers which will throw off your measurement when using bump gauges and especially for the resizing process itself.

 

[Deleted member 10043]

You can measure a case that is primed properly.

 

[_Windrider_]

You can measure a case that is primed properly.

An Unfired primer right? If you are measuring a fired case you should remove that primer no?

 

[spife7980]

An Unfired primer right? If you are measuring a fired case you should remove that primer no?

You can measure a fired primer just fine... provided it isnt proud of the case face.
That means primer flow/cratering would have to be reseated/pushed flat. But it is sooo much easier to just run them through a $15 universal decapping die and not have to worry about anything of the sort.

 

[_Windrider_]

You can measure a fired primer just fine... provided it isnt proud of the case face.
That means primer flow/cratering would have to be reseated/pushed flat. But it is sooo much easier to just run them through a $15 universal decapping die and not have to worry about anything of the sort.

That's kind of what I was always taught so I just wanted to clarify.