Got my brass prep and reloading heads set up for my xl650. Sized my first batch of brass, and have a question. I'm using a Hornady case comparetor to check

the finished brass size. Using factory PMC and AE for baseline measurements, I'm getting 1.4545 - 1.4565 brass length. After resizing my brass through a 1200b  

trim die and trimming to length, I'm getting 1.4545 - 1.4570 on 80% of the cases. This is the length I set up for. However, 20% of the cases are coming up short

around 1.4525 - 1.4535. When I put these cases into a JP case gauge, as close as I can tell, they are right at the minimum step on the gauge. Looks like my shortest case is

about .0020 shorter than factory loads. OK to load these shorter ones?

Better way to get an exact headspace measurement?

How much case length variance is normal for a progressive press set up with a 1200 size/trim die?

Cases are all PMC, clean, and lubed with DCL.

Might be elementary questions, but I'm just starting into rifle reloading, and I want to get it right.  THANKS!!

Trim length depends on headspace (with some trimmers). If your not actually resizing the case (the case headspace is less than your resizing die setup) then your trimmed brass will be shorter.

This means you will have some brass that was resized and trimmed, and some brass that was not resized but still trimmed.

I typically setup my trimmer so that brass that has the correct headspace will be trimmed to the correct level and once fire formed, the rest of the brass will slowly reach that point.

Minimum case length isn't that big of a deal, too long can be a huge deal! Just make adjustments to keep brass from being too long and don't worry about the shorter brass.

To check and see if what I'm telling you is correct, see if the brass with the shortest headspace also has the shortest case length (it definitely should).

2 measurements that you refer to that can be confused.

Brass trim length is what the total length is from end to end.

Headspace length is what you measure with your Hornady tool. Distance from base to datum point on shoulder. This is your headspace of the round.

Measure a fired round FROM YOUR RIFLE.  Adjust dies to make this measurement .003-.004" less for semi-auto, .001-.002" less for bolt.

It sounds like you might be bumping it too much. Measure a fired round, then a sized round, with your Hornady tool, difference is how much you are bumping the shoulder back.

As was posted short is not a problem but long is. I run into the same problem with my Dillon die. After sizing then running them through my WFT trimmer I get overall lengths all over the place. None are too long so I do not worry about the short ones.

Vince

Brass trim length is 1.750" for .223.

Hornady's Lock-N-Load, RCBS's micrometer headspace gage or Mo DeFina's micrometer headspace gage will give you case shoulder bump measurements in .001" increments.

Drop in gages, while better than nothing, pretty much suck.

You are trimming your cases way too much if you case length is only 1.425" to 1.435". Screw the trimmer up (CCW) to get a longer case length.

Thanks for all the replies so far. I need to get better at explaining my data. The 1.4545 measurements are from the shoulder of the brass to the base. The Hornady

Comparetor does not measure from the datum line, so it is just a reference number (according to Hornady). I did not list what my trim lengths were, but they are ~1.7520,

which I believe is good. Here's the part I guess I am confused on - The case headspaces on the shoulder, so if the case length is shorter, then the clearance

between the case base and the face of the bolt is increased, too much space here is bad? Too tight worse on an AR? I do not have a case that I can assurably say was

fired from my particular rifle, because when I go to the range I usually take a couple rifles, and my friends bring theirs, and I keep all the brass. Guess I need to go to the

range and make some empty brass. Thanks again for the replies. I enjoy the reloading part as much as shooting (well, almost...) and the more I learn the more fun I have...

The comparator does measure from the datum.

If you have inconsistent trim lengths and you want to ensure all your ammo will feed in all your rifles, you could bump your shoulder back to 1.450" (which should actually size all your brass). Since all the brass should be sized at this reduced headspace you should get much, much more consistent trim lengths.

Like was stated above, this is a know problem. I traded some brass with a friend and he was pissed my trim lengths were all over the place. I only size my headspace to 1.460" (perfect for my gun)  so a lot of the brass was never sized. Since I trim on a giraud (which trims based on headspace), the ones that were shorter end up getting trimmed shorter than the ones actually resized. In other words, the datum to case tip is always trimmed the same, but the datum to base length is different and thus your case length is different.

Like I said, I setup to size and trim max length and don't worry about the stuff under, they will get there after a firing or two.

As for fired cases, just take a bunch of brass that have headspace too large for your gun and make your own go/no go gauges to check your headspace. So size a case go 1.465", 1.464"...... 1.450" and use these gauges to test the headspace in all your rifles. They'll last forever. It's a bit more difficult in semiautos compared to bolt action, but it will clue you in without having to fire your rifle.

Edit: I misspoke in my previous post, all brass will be trimmed if it trims based on headspace. I updated the post.

Don't size too small.

Don't trim too short.

The variation you report is perfectly normal.  There isn't really any point in chasing it.  If you're seeing stuff that's 0.005" or more out, then I'd start looking at your case lube and how it's applied.  Even that, on the short side, would be fine to fire; your cases just aren't going to hold up as long.



As far as a more precise measurement--three digits is plenty (e.g. 1.454").  Four (e.g. 1.4545") isn't meaningful.  Even if the caliper was at some point honestly calibrated to that, all bets are off with the introduction of Hornady's bushing.  Plus we're measuring something that is soft and was tossed around on the ground.  Chamber headspace is sometimes measured to four digits, but that's with a calibrated hardened steel gage under closely controlled conditions and is still more art than science.  

About the only time it's worth measuring 4 digits yourself is when slugging bores/cylinders.






 


Set the shoulder on the brass fired from your rifle back by 0.002" on average (or set the die per mfr instructions and check against factory ammo if you don't have brass fired from your rifle).

Hornady doesn't guarantee measurement from the true datum line using their tool. But by always using the same collet you establish your own datum line . . . which is why Hornady calls it a "reference point".

Are you absolutely certain those short cases weren't short before resizing? The shoulder cannot*** be bumped up (ie made longer to the shoulder) during resizing . . . it can only be done by firing in your chamber. Pretty sure those cases were that short before you started.

Why did some cases fail to lengthen when fired in your chamber? Not enough pressure to do that. Why not enough pressure? Beyond my knowledge. But I do know it happens all the time.

Yes they are as safe to fire a second time as they were the first time.

*** actually it can be pulled up a couple thousandths as you remove the expander ball when withdrawing the case from the sizing die. While that can contribute to tiny variations in shoulder height, it is irrelevant to our purposes here.

There is some confusion on the terms that you are using:

Case length = length measured from case mouth to base of case. The whole thing.  Before or after trimming, same method.  Measured with bare calipers.

Headspace measurement =  measurement from base up to datum (reference point) on the shoulder.  Your Hornady gauge measures this.

Your ideal headspace setting (set by sizing dies) would be a few thousands shorter than after it was fired.  If it is too loose it shortens case life.  If it is way too loose, it might not even go off.  Too tight and it won't chamber at all.

You have the unique ability to change both of these measurements in the same die.  You have two adjustments to worry about.  The height of the die above the cartridge base (sets headspace) and the height of the cutter head (sets case length).  After carefully setting both of those you can make short work of processing brass.

To get this setup ideally, you would use a case fired in the rifle you plan to shoot this ammo in.  If you want to make it work in all rifles, use the factory ammo as a reference point to set up your die.

And yes, only 3 significant digits are required.  Enjoy!

OP- First off, I have no problem distinguishing between your references to headspace and to overall length. And, with the rapid trim, press variations affect both simultaneously.

Brass will spring back after sizing by a small amount. Some people size twice in progressives, once slightly larger then a second tome to fine-tune. I also bump the handle up then back down slightly when processing brass- I think it helps clean up the cut edge of the case mouth as well.

Additionally, one problem with progressive presses is small variations in length also occur with variations in brass population. Toolhead and shellplate loading varies based on whether brass is being sized or not, and on a 1050, the swager affects this as well. I test sized several groups and the first and last pieces were where the largest variation was seen,

On my old 650's I last experimented with a sizing die in station 1 to pre-size and knock out the primer, and sizer/trim die in station 3. I had to make a short pin to fit under the blue vacuum adapter (manifold). could also have notched the manifold halves, also. IIRC I then used a Lee sizing die in station 5 with the die body set high and the decapper set low so that the decapper/expander opened the case mouth up and also helped shear any burrs left inside the mouth edge.

I am still working on this concept, and now have 1050's. Am doing similar to the die setup mentioned above- Now the first die is a Lee universal decap die. The last die is a Lee universal decap die body with a .223 expander. Adjust the die body of both down to slightly preload against the shellplate.  This forces the loading between shellplate and toolhead to be consitent and eliminated a lot of the variations I saw otherwise.

I am going to put powder die bodies in unused positions on each side of the RT-1200 as well, I will probably have to cut them down to fit under the vacuum adapter.

I use a chamber gauge to force the Hornaday comparator to give me real numbers- I insert a 1.630 308 chamber gauge, and rotate the dial to read that number. Digital gauge would require some creativity. You could also try zeroing on a known piece of brass/new factory ammo then readings will be a + or minus indication from that reference.