Case web expansion help

[Kroberts]

I measured the case web expansion of the load I've been running in my 284win. These cases were on there 2nd firing when I measured the expansion. Of the 5 cases I took measurements in I got an average expansion of 0.0028". With a high of 0.0036" and a low of 0.0015". What I'm confused about, is which gigot is used to determine whether or not the load is safe and an approximate pressure. This load has had a good doped spread with an aberage across 20 shots of about 12-15fps ES with this checked several times, with 5 shots typically around 10fps. And groups well with the average 5 shot 100 yard group hovering around 0.25-0.375". Is it normal to have that much variation in web expansion? These cases havmt had the donuts removed yet. I didn't realize the reamer is for expanded necks, not sized necks. And I had already resized the cases before I discovered this. The attached images should be my case web numbers. I've been running this load for a while and got 12 loads out of my first batch of brass, which in happy with the life. So I'm not too concerned about changing my load. I'm more interested in learning to more accurately read pressure signs for load decelopment.

So what do you all think.

Thanks,
Kyle

 

[CatShooter]

I measured the case web expansion of the load I've been running in my 284win. These cases were on there 2nd firing when I measured the expansion. Of the 5 cases I took measurements in I got an average expansion of 0.0028". With a high of 0.0036" and a low of 0.0015". What I'm confused about, is which gigot is used to determine whether or not the load is safe and an approximate pressure. This load has had a good doped spread with an average across 20 shots of about 12-15fps ES with this checked several times, with 5 shots typically around 10fps. And groups well with the average 5 shot 100 yard group hovering around 0.25-0.375". Is it normal to have that much variation in web expansion? These cases haven't had the donuts removed yet. I didn't realize the reamer is for expanded necks, not sized necks. And I had already resized the cases before I discovered this. The attached images should be my case web numbers. I've been running this load for a while and got 12 loads out of my first batch of brass, which in happy with the life. So I'm not too concerned about changing my load. I'm more interested in learning to more accurately read pressure signs for load development.

So what do you all think.

Thanks,
Kyle

"What I'm confused about, is which gigot is used to determine whether or not the load is safe and an approximate pressure. "

You cannot use head expansion to judge pressure or load safety. It is impossible because the expansion tells you nothing.

 

[velvetant]

I'm only assuming here but I think you are measuring the case expansion ring. All that tells you is your chamber is tight or sloppy.
If you are after case head expansion you need to be out 4 decimal and anything over .0005 is considered a hot load.
You need to use a blade micrometer to get the area just above the extractor groove any further up and you start getting back into the expansion ring.

 

[CatShooter]

I'm only assuming here but I think you are measuring the case expansion ring. All that tells you is your chamber is tight or sloppy.
If you are after case head expansion you need to be out 4 decimal and anything over .0005 is considered a hot load.
You need to use a blade micrometer to get the area just above the extractor groove any further up and you start getting back into the expansion ring.

the problem with this "method" is that there is a wide variation in the hardness of brass in cartridge cases, and heads.

I have measured case heads with a very good hardness gauge, and the Lapua - Norma, Lake City are about TWICE as hard as the Remington - Hornady etc group.

So, what is a 50,000 psi load in a Rem case, will need 100,000 psi inn a Lake City or Lapua to match.

It is just not possible to use case expansion for a realistic gauge.

I've been there, and got the tee shirt (in spades).



http://bulletin.accurateshooter.com...r-brass-5-56-and-223-rem-base-hardness-tests/

 

[bigedp51]

Measuring base expansion just above the extractor groove tells you how much pressure that type and brand of case can take.

Example below, the thickness of the flash hole web adds radial strength to the base of the case.
Below the Lake City 5.56 case on the right has harder brass in the base and a thicker flash hole web. And I had 2005 dated factory loaded Federal .223/5.56 cases with over sized primer pockets after the first firing, and these Federal cases had thinner flash hole webs

Below case flash hole web thickness with Federal having the thinnest flash hole web and the base expands more when fired.

So again, measuring base expansion doesn't tell you the chamber pressure. "BUT" it does tell you how much pressure that caliber and brand of case can take.

Below the hardness of the brass in the base, the base wall thickness and how thick the flash hole web is governs how strong and how much pressure can take.

Measuring base expansion tells you the elastic limits of the brass. And similar to brass flowing into the ejector and exceeding the elastic limits of the brass.

Simple Trick for Monitoring Pressure of Your Rifle Reloads | Hodgdon Reloading

To the OP, try another brand of case and look for cases built Ford Truck Tough.

 

[Mikecr]

+1 bigedp51
I measure webs for 'MyMax' which is a point of runaway(yielding beyond fireformed plateau), where lower body sizing would be required each cycle. This does not tell me the actual pressure. I base pressure off QuickLoad estimates for the load it took to get there.
Again, not a direct measure of actual pressure.

 

[Rounder]

Bend a small 90 degree head on a paper clip and feel inside
the case at the expansion ring for cracking.

 

[CatShooter]

Bend a small 90 degree head on a paper clip and feel inside the case at the expansion ring for cracking.

Stretching and cracking are caused by headspace, not pressure.

If you can feel the stretching with a paperclip, it is bad, but by then, it is too late.

By the time it is cracking, you WILL see it immediately. But neither stretching or cracking are caused by pressure.

 

[AZShooter]

You mentioned a donut. What brass are you using? Are you by any chance using 6.5-284 Lapua brass and necking it up? I have used Winchester 284 brass for over 30 years. I have never encountered a donut.

Just in case you are not aware, Bullets.com has Norma 284 brass that they had made for them.

Bullets.com™)

If I didn't have so many pieces of Winchester brass this is what I would use.

The brass is made to very high standards. From Accurate shooter:

"Bullets.com's contract with Norma calls for advanced production methods to make sure the new brass is truly "match-grade" and long-lasting. To ensure that primer pockets stay tight for many firings, the caseheads on the new brass will be double-stamped for improved hardness and strength. Additionally the new brass will go through an additional draw stage to ensure ultra-uniform casewall thickness. With these extra manufacturing steps, this .284 Win brass should be the best brass Norma has ever produced"

 

[Kroberts]

Thanks everyone,
It is necked up lapua brass. At the time I bought it Norma hadn't come out with, or I didn't know about the Norma brass. If asked about it before and was essentially recomended to stick with the lapua. But I'm not too picky what I use as long as it works well. I finally made it through them all to be able to fully prep the brass. Which means remove the donut and neck turn to clean up the uneven thickness from expanding. I've noticed that it's not uncommon in necked up lapua brass to have one side about 1 thousanth thicker than the other. That much night not make a huge difference. But why not correct it if I can.
The micrometer in using goes to the 4th decimal place, but it's not a blade style. It one that had the 5/16" circle platforms that meet. So I might not be getting the measurement exactly where it needs to be then. I wonder if I could make tgin blades that fit on the micrometer to get accurate measurements. It's sounding like these measurements are a way to ensure good brass life while maintaining good performance.

Thanks for the info everyone.

Kyle

 

[bigedp51]

Stretching and cracking are caused by headspace, not pressure.

If you can feel the stretching with a paperclip, it is bad, but by then, it is too late.

By the time it is cracking, you WILL see it immediately. But neither stretching or cracking are caused by pressure.

CatShooter old buddy, below is my $100.00 bent paper clip or RCBS case mastering gauge measuring case stretch. The factory loaded .303 British case stretched .009 on its first firing.

So CatShooter if you pay enough for your bent paper clip it can help a great deal.

 

[Mikecr]

I'm sure CatShooter is trying to keep the context in discussion about expansion and pressure, instead of stretch. And his statements on stretching/cracking are correct.

 

[bigedp51]

I'm sure CatShooter is trying to keep the context in discussion about expansion and pressure, instead of stretch. And his statements on stretching/cracking are correct.

Head clearance is the distance the base of the case has to stretch to meet the bolt face. But the strength of the brass and case design governs if and how much the case will stretch when fired.

The thin Winchester case in my photo above stretched .009 "BUT" my Prvi Partizan cases did not stretch when fired in the same Enfield rifle.

Both cases below were fired in the same .303 British Enfield rifle. The Priv case did not stretch or thin when fired because of brass hardness and its design. The Priv case is larger in diameter, and is .010 thicker in base wall thickness than the Winchester case.

Example a Federal .308 case will expand more in the base and also stretch and thin far more the a Lake City 7.62 case with its thicker and harder case.

Bottom line the quality of the case and its construction governs stretch and base expansion, So measuring stretch and base expansion will tell you a great deal about the quality of your cases.

I buy bulk Lake City 5.56 and 7.62 cases and some of it was fired in machine guns and I find very few that stretched and thinned. So military cases are made Ford Truck Tough.

CatShooter and I are good friends, and we met arguing over CatShooter lubing his cases to keep them from stretching. I learned a great deal about headspace and case construction by collecting British Enfield rifles. And I played with my bolt heads until I nearly went blind.

The OP stated he has over .002 base expansion with top grade Lapua brass. The OP is either loading too hot or measuring the case in the wrong area. And if the OP does not have any brass flow into the ejector then my guess would be he is measuring the case in the wrong area.

 

[Mikecr]

The OP stated he has over .002 base expansion with top grade Lapua brass. The OP is either loading too hot or measuring the case in the wrong area.

Or, his chamber is simply 2thou or more in clearance near webs.
Doesn't for sure mean he's over pressure or measuring wrong.
Also, with 'top grade' Lapua, are you talking about brown, or blue box?