Case web expansion help

[bigedp51]

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?

1. It doesn't matter what diameter the chamber is, or the diameter of the case, your measuring the "unsupported" area "outside" of the chamber just above the extractor groove.

2. And if you looked at the link CatShooter posted of his rockwell hardness tests the only brass harder than Lapua were the Lake City cases. Meaning Lapua has the hardest brass in their cases of any of the other commercial brands of cases.

The photo below came from AccurateShooter.com reloading forum posted by a competitive shooter that was shooting to 1000 yards. This shooter increased his load until he had brass flow into the ejector. He then backed off 1 or 2 grains of powder and started looking for his best groups.

So again my guess is the OP is "NOT" measuring the case just above the extractor groove and why he measured over .002 base expansion. And the reason for this guess is because the OP said nothing about brass flow into the ejector.

 

[Kroberts]

I looked over my brass a bit last night while doing a little prep work and sizing it. There is no brass flow anywhere. Only the slightest mark showing where the ejector is in a couple of cases. But there more of a shiny spot from the case thrust. And I was definitely measuring the point right above the web. There was a very slight, but still distinctive swell just after the web if you looked at it closely. So that's probably what I was measuring. Being a rebated rim case. I could probably get te micrometer to work by using the very edge of the measuring posts on the brass. Think I could get good measurements on the third firing of brass? Though I'm sure im within the working limits of the brass. And it's the blue box lapua. I actually had to look up what the brown box lapua was, since Id never heard of it.

Kyle

 

[Mikecr]

I don't measure unsupported area, but the webline. That is, the area expanded to max(which is not usually an unsupported area) at the breach. I'm sure this is what OP is doing as well.

 

[bigedp51]

Below from the Hodgdon powder website.

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

One of the first rules of handloading is to always follow the approved reload data. The cautious reloader gradually works up to approved maximum loads to ensure his particular gun does not show pressure signs. Generally this is visual observation of the fired shell case head and primer. There is another slick way to check for pressure signs if you are interested.

Using a blade micrometer that measures in ten thousandths (.0001"), new, unfired cases can be gauged before and after firing to determine reasonably accurate maximum loads. Micrometers measuring in thousandths (.001") are insufficiently accurate to perform these measurements, and should not be used. Previously fired cases cannot be used accurately due to various levels of brass hardening. Measurement is taken just ahead of the extractor groove on the case head and must be taken at the same place on the case before and after firing. By placing a small mark on the case head – entering the cartridge in the chamber with mark at 12 o'clock – a consistently accurate measurement can be taken with each firing.

Lower pressure rounds, like the .30-30 Winchester, usually yield maximum pressures at .0003"-.0004" expansion. Modern cartridges, like the .223 Remington, will show maximum pressure at .0004"-.0005", while .308 Winchester, .270 Winchester, etc., typically yield .0005"-.0006" expansion at max pressure. Magnums, like the .300 Winchester Magnum, show maximums at .0006"-.0007" expansion, and should be measured on the belt.

In conjunction with these measurements, case head signs of pressure should be monitored as well. These signs include very flat primers, slightly cratered primers, ejector marks on the case head, and stiff extraction. All these case head signs indicate high pressure, and loads should be reduced until these signs disappear.

As always, start with the beginning load listed, and cautiously work up to the maximum shown for that set of components, using the methods listed herein.


As posted before the two cases below were fired in the same .303 British No.4 Enfield rifle, noted for their larger diameter chambers and longer headspace settings. The expansion ring on the Greek HXP case is more pronounced because of the cases smaller base diameter and thinner case walls. Measuring this part of the case means nothing because as you can see the Prvi Parizan case is a larger diameter and .010 thicker in this area. Meaning smaller diameter cases with thinner case walls will expand more than larger diameter and thicker cases.

Again this is why I buy bulk Lake City cases that have harder brass in the base and thicker flash hole web that adds radial strength to the base just above the extractor groove.

Part of the early jamming problem with the M16 rifle was soft brass brought out in the 1968 Congressional hearings. And the cases were made harder in the base at Lake City and commercial contract ammunition made for the military.

The photo below came from AR15.com and shows a 2 inch rod that fits inside the case to measure flash hole web thickness. The reason for this check is because Federal cases had the thinnest flash hole web and had "MORE" base expansion causing oversized primer pockets.

Base expansion just above the extractor groove will show you that you are over stressing the brass beyond its elastic limits. Meaning over sized primer pockets that can cause gas leakage and a etched bolt face.

And now the funny part, the person who posted the photo below said he didn't worry about loose primer pockets. And he would just replace the bolt when it became bad enough.

Bottom line measuring higher up the case where the case expands to meet the chamber walls means nothing. All this tells you is how much smaller in diameter the case is than chamber diameter. And measuring just above the extractor groove will tell you if you are over stressing the base of the case from more chamber pressure than the base can take.

 

[Mikecr]

Bottom line measuring higher up the case where the case expands to meet the chamber walls means nothing. All this tells you is how much smaller in diameter the case is than chamber diameter. And measuring just above the extractor groove will tell you if you are over stressing the base of the case from more chamber pressure than the base can take.

I agree that increasing load measurements nearest the extractor groove can assist in prediction of loosening primer pockets. If you're trying to stop a primer pocket issue, this could help you to determine a max for your load. That's one pressure 'problem'.
Another pressure 'problem' can be popping extraction. My webline test keeps me clear of that, and with it I haven't lost cases to loosening pockets(except from Norma brass). Good with Lapua brown box & Winchester reloading brass.

 

[bigedp51]

I agree that increasing load measurements nearest the extractor groove can assist in prediction of loosening primer pockets. If you're trying to stop a primer pocket issue, this could help you to determine a max for your load. That's one pressure 'problem'.
Another pressure 'problem' can be popping extraction. My webline test keeps me clear of that, and with it I haven't lost cases to loosening pockets(except from Norma brass). Good with Lapua brown box & Winchester reloading brass.

No offense or criticism intended Mikecr on what I have been saying or about to say.

I full length resize my cases and I think you neck size which effects our meanings in what we are posting. And because of this I think we need to say what sizing method is being used by the OP.

Example on a semi-auto like a AR15 and M1A the "full length" resized case should be .003 to .005 smaller in diameter than its fired diameter for reliable extraction. But since you are neck sizing I will assume you measure farther above the extractor groove where the case has expanded to meet the chamber walls. This is because you reach a point where this area will bind and drag on the chamber walls durring extraction. And at this point you use a body die to reduce the body diameter and bump the shoulder.

Bottom line I'm not sure if the OP is neck sizing or full length resizing "BUT" the title of the OP posting is "Case web expansion help" and this is just above the extractor groove and not further up the case. Clarification of what the OP is trying to do and where and why he is measuring would clear things up.

 

[Kroberts]

Pretty much what I'm trying to find is that I'm getting the most performance I can while maintaining the primer pockets as well as I can. I think I was measuring a bit too far forward due to how wide of a measuring surface the micrometer has. At the moment that is a 180gr SMk at ~2900 fps from a 32" barrel using 55gr of H4831. And getting 10 loading from the blue box lapua brass before the pockets start to get loose and on the 12 loading there is no resistance while seating the primers, but they stay put. I'm using a forster full length sizing die so that it just bumps the shoulder for easy feeding. I have no idea if the actual amount of bump. But if I back out the die about 1/32 of a turn then the cases get very difficult to chamber after a couple firings. Due to a fairly large chamber neck I anneal the cases every 2nd firing.

Kyle

 

[Rounder]

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.

what is the reason for the paper clip ?

 

[parshal]

I have no idea if the actual amount of bump. But if I back out the die about 1/32 of a turn then the cases get very difficult to chamber after a couple firings.

I've found the same thing but I do measure the shoulder bump. Sometimes it's not the shoulder making it difficult but the size of the case near the base. Measuring that spot with normal calipers is quite difficult. I'd suggest getting the Hornady comparator and measuring the shoulder to see if it's the should or the base causing the difficult bolt. My loads are all hot and I find it's the base that needs resizing after before the third reload.

With a paper clip down in the case you can feel the thinning of the brass above the web. By the time you feel it, though, it's already too late. Case head separation is imminent. I speak from experience on that one having over annealed a batch a brass!

 

[Rounder]

I've found the same thing but I do measure the shoulder bump. Sometimes it's not the shoulder making it difficult but the size of the case near the base. Measuring that spot with normal calipers is quite difficult. I'd suggest getting the Hornady comparator and measuring the shoulder to see if it's the should or the base causing the difficult bolt. My loads are all hot and I find it's the base that needs resizing after before the third reload.

With a paper clip down in the case you can feel the thinning of the brass above the web. By the time you feel it, though, it's already too late. Case head separation is imminent. I speak from experience on that one having over annealed a batch a brass!

Thanks

 

[bigedp51]

what is the reason for the paper clip ?

Causes of Case-Head Separation
http://www.accurateshooter.com/technical-articles/case-head-separation-cause-diagnosis/


I use the RCBS case mastering gauge below that can measure stretching and thinning more accurately to a .001 of an inch than a bent paper clip.