6.5 Creedmoor brass keeps getting shorter??

I’m heading to the range now, I’ll measure the cases when I get back, before and after resizing.

I measure my cases before and after resizing,for length.

I don’t have a set of go-nogo gauges, but is it possible to get an idea of headspace, using tape?

And if I have to much headspace,could I screw the barrel in ,using a dummy round? Lol
 
View attachment 379519I just measured two cases ,before and after.

As you can see, not much has changed ,except for neck tension.
Maybe I should have meantioned that I was doing load development as well.
So maybe now that I’m content with the load I’m looking for , they’ll stop shrinking?? Lol
Should I leave them all as is , being different lengths?
Or should I trim them all to the shortest length case?
 
Measure a resized case from the case mouth to the base of the case and write it down.

Next put a fired spent primer in the primer pocket of your resized case with just your fingers. Then chamber the case letting the bolt face seat the primer and extract.

Now measure the case again from the case mouth to the base of the primer and write it down.

Now subtract the first case measurement from the second and this is your head clearance. Meaning how much shorter the case is vs the actual chamber headspace.

Normally your head clearence is how far the shoulder was bumped back by the die. And the case should be .001 to .002 shorter than actual chamber headspace for a bolt action.

HK76WCp.jpg
 
View attachment 379567View attachment 379566
bigedp51 said:
Measure a resized case from the case mouth to the base of the case and write it down.

Next put a fired spent primer in the primer pocket of your resized case with just your fingers. Then chamber the case letting the bolt face seat the primer and extract.

Now measure the case again from the case mouth to the base of the primer and write it down.

Now subtract the first case measurement from the second and this is your head clearance. Meaning how much shorter the case is vs the actual chamber headspace.

Normally your head clearence is how far the shoulder was bumped back by the die. And the case should be .001 to .002 shorter than actual chamber headspace for a bolt action.

HK76WCp.jpg
Click to expand...
 
I'm not sure what you mean by your above posting, how far does the primer protrude using the method I posted.

I do not need your chambers headspace, I want to know how far you are bumping the case shoulder back during sizing. Meaning what is the cartridge headspace vs the chambers headspace and why the case length isn't getting longer. The amount the primer protrudes is how far the shoulder was actually pushed back during sizing.

If you have the proper amount of shoulder bump your die could be on the plus side in diameter and simply not squeezing the case enough to make it grow in length.
 
Sorry the pictures are showing two different things.
The first set of pictures show a sized case 1.905, then with the primer after closing the bolt it’s 1.914. So it’s .009

The picture with the tape is a completely different issue.
 
Call me lucky.. I got a chance to fire 20 rounds from my 6.5 CM yesterday too.

My chamber is what I'll call "normal", i.e. brass behaves as I would expect it to.

I know 10 of my cases were slightly above 1.910" when I started (new brass that had been deburred, sized, and measured) As I recall, most were 1.912", with a few at 1.913"-1.914". None were longer than that.

I also know that from head to shoulder datum was between 1.556" and 1.558" on every case, that got measured too.

This is what happens when I have idle time during a pandemic, I stretch out the little jobs to make them last ☺

The other 10 were 8x fired, freshly annealed brass that had plenty of chances to fireform to my chamber. Also within 1.910" and 1.914" overall. If it had been 1.915" it would have been trimmed.

I trim at 1.915", not 1.920". It doesn't need to be done, it's just the way I do things.

I know which cases were new, and which were 8x fired, they were both marked.

I'll measure the cases before I do anything to them, and at each step til they're ready to load again.

If nothing else, it'll give the OP some insight into what another member is seeing with the same brass he's using, which is Lapua small primer 6.5 CM brass.

My load is a 123 gr Sierra Match King over H4350, at 2850 fps. It's a moderate load by most standards. The cases stretch slowly, they almost never fully form to the chamber in one firing.
 
45C said:
Sorry the pictures are showing two different things.
The first set of pictures show a sized case 1.905, then with the primer after closing the bolt it’s 1.914. So it’s .009

The picture with the tape is a completely different issue.
Click to expand...

If the primer is protruding .009 it means you are bumping the case shoulder back too far. The primer should only be protruding .001 to .002 and the base of the case will have less distance to stretch when fired.

What the .009 primer protrusion means is the case has to stretch .009 to contact the bolt face when fired. This will cause a case head separation due to the stretching and thinning of the brass.

Below I'm using a Hornady cartridge case headspace gauge and measuring a "FIRED" .223 case from my AR15. I then adjust the die for .003 shoulder bump meaning .003 less than what the gauge is showing.

OJqNmQH.jpg
 
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Ok... lots of information to be shared. If you're interested it's not too bad, if you don't want to wade through all the numbers that's fine too.
I've been trying to get a handle on how much my brass "grows" with every firing, this project did that in spades!

I certainly don't measure like this for every loading! I'm OCD, but even that has limits. I usually check a few cases for head-to-shoulder distance in every batch I size, and I do measure each case for length every time around, but that's about it.

First, the tools and material I'm using..
I had 20 fired 6.5 CM cases from Sunday. 10 are once-fired, 10 have been fired 9 times.
It's a moderate load, 123 gr Sierra Match Kings traveling at 2850 fps, driven by H4350.
The rifle is a Savage 10T, 24" heavy barrel.
I'm using a set of basic RCBS full length dies, they're hardly high tech.

The tool I have to measure to the shoulder datum is a piece of brass round stock exactly 1.000" long, with the center bored to 0.375", which is the same diameter as the center of the shoulder on the 6.5 CM case. A Hornady headspace gauge does the same thing.

nIGLmZT.jpg


Used with a dial caliper, you simply deduct 1.000" from every measurement you take.

LiBuBst.jpg


I use it to check my case length to the shoulder. I know that a case that's 1.562" long to the shoulder is a snug fit in my rifle. Any longer than that and the bolt is hard to close. I aim for 1.560" to the shoulder when I set up my die.
I'll spread this over a couple of posts.
 
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Now for the tedious part.

Since this thread was about brass getting shorter, rather than longer, I wanted to capture the way brass "flows" as it gets stretched and moved around both by firing and then by resizing it.

I took 12 measurements on each case, 7 after it was fired, and 5 after it was resized.

Bigedp51 mentioned measuring with the primer in place. I usually measure with it out, but leave no stone unturned, right?
The only trouble with the primer "in" method is if you have cratered primers. The raised crater lip will give you a false reading. My rifle with this load doesn't crater much, if at all, so it's not too bad.

I also measured with the primers removed, before the cases were sized. I deprime off the press.

I measured three areas on the case diameter, A is just below the shoulder, B is mid body, and C is just above the extractor groove.

e0NvMsW.jpg
 
The actual data is in this post. I've tried to make it as easy to read as possible.

0SiPKip.jpg


9x fired brass is up first.
WuoCPZp.jpg


Then once- fired brass..
cfeJso4.jpg


And measurements from unfired Lapua brass. They're considerably smaller before firing! One size fits all.
T9qK66j.jpg
 
I'm lucky in that even a basic RCBS die gives me very close to what I want for a finished product. The brass doesn't get over worked, which should result in fairly long life. I anneal every 4th firing.
I was surprised that the new brass I have fire formed to the chamber very quickly. As I said earlier, it's a fairly light load, but it gets the job done. I seem to recall my last batch of Lapua brass took 3-4 firings before it filled the chamber. This one is a good fit after one time around.
Looking through the data quickly, it seems like most of my cases have gotten about 0.003-0.005" longer with each firing. That roughly what I suspected, I usually trim about 30-40% of them at each loading. In other words, if I have 30 cases to prep, 10 will need to be trimmed on average.
 
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