I've got a couple instances where I really think I need to understand, fully, the web expansion method to recognizing high pressures. Problem is......I'm not real well versed in what I need to be looking for.

First scenario is a .375 Wby. I'm about to begin load development for. Reloading data is not in abundance for it. So I figured if I used max. H&H charge weights as a starting load and worked up, I'd be alright. I have 6 fired rounds from this rifle. All were "near-max" book loads built on new Wby./Norma brass. I have miked the cases directly ahead of the belt before & after firing and have, I guess, a reference number to go by. How do I use that number to determine what would be excessive expansion on future loadings??

Second scenario is not that different than the first, I guess. I am developing a load for a 7-STW. using Layne Simpson data (and actually 1 gr. under what he calls max.) I am getting exceptionally quick chrono numbers with none of the "layman's" pressure signs.......ugly primers, extracter marks, sticky bolt. I'm guessing the same method of expansion monitoring that would work for the above would be my smartest way to go here too.

How much expansion is too much?? Is my baseline in the .375 instance a valid one?? Thanks for any help in advance. 'Preciate it!!

for starters....here's some max loads from Hodgdon for the .375 weatherby
225 Hornady SP Hodgdon H-4831 99.0 2,957
Remarks: compressed load; dia: .375"; col: 3.585"; 49,600 cup
225 Hornady SP Hodgdon H-4350 94.5 3,070
Remarks: dia: .375"; col: 3.585"; 53,400 cup
225 Hornady SP Hodgdon H-414 96.0 3,044
Remarks: dia: .375"; col: 3.585"; 49,600 cup
225 Hornady SP Hodgdon H-380 87.0 2,980
Remarks: dia: .375"; col: 3.585"; 53,900 cup
225 Hornady SP Hodgdon Varget 74.5 2,850
Remarks: dia: .375"; col: 3.585"; 53,500 cup
225 Hornady SP Hodgdon H-4895 73.5 2,896
Remarks: dia: .375"; col: 3.585"; 53,100 cup
235 Speer SP Hodgdon H-4831 99.0 2,912
Remarks: compressed load; dia: .375"; col: 3.585"; 50,500 cup
235 Speer SP Hodgdon H-4350 90.5 2,952
Remarks: dia: .375"; col: 3.585"; 52,600 cup
235 Speer SP Hodgdon H-414 95.5 2,940
Remarks: dia: .375"; col: 3.585"; 48,200 cup
235 Speer SP Hodgdon H-380 83.0 2,849
Remarks: dia: .375"; col: 3.585"; 52,400 cup
235 Speer SP Hodgdon Varget 73.5 2,774
Remarks: dia: .375"; col: 3.585"; 52,700 cup
235 Speer SP Hodgdon H-4895 73.3 2,834
Remarks: dia: .375"; col: 3.585"; 53,100 cup
250 Sierra Soft Point Boat Tail Hodgdon H-4831 97.0 2,871
Remarks: compressed load; dia: .375"; col: 3.600"; 52,500 cup
250 Sierra Soft Point Boat Tail Hodgdon H-4350 88.0 2,873
Remarks: dia: .375"; col: 3.600"; 52,300 cup
250 Sierra Soft Point Boat Tail Hodgdon H-414 93.0 2,939
Remarks: dia: .375"; col: 3.600"; 51,500 cup
250 Sierra Soft Point Boat Tail Hodgdon H-380 79.5 2,743
Remarks: dia: .375"; col: 3.600"; 52,200 cup
260 Nosler Partition Hodgdon H-4831 96.0 2,810
Remarks: compressed load; dia: .375"; col: 3.585"; 53,200 cup
260 Nosler Partition Hodgdon H-4350 88.0 2,818
Remarks: dia: .375"; col: 3.585"; 53,300 cup
260 Nosler Partition Hodgdon H-414 91.0 2,842
Remarks: dia: .375"; col: 3.585"; 52,400 cup
260 Nosler Partition Hodgdon H-380 78.0 2,655
Remarks: dia: .375"; col: 3.585"; 52,900 cup
270 Hornady SP Hodgdon H-4831 96.0 2,787
Remarks: compressed load; dia: .375"; col: 3.600"; 53,600 cup
270 Hornady SP Hodgdon H-4350 88.0 2,787
Remarks: dia: .375"; col: 3.600"; 52,800 cup
270 Hornady SP Hodgdon H-414 90.0 2,842
Remarks: dia: .375"; col: 3.600"; 53,400 cup
270 Hornady SP Hodgdon H-380 78.5 2,678
Remarks: dia: .375"; col: 3.600"; 54,100 cup
285 Speer GSSP Hodgdon H-4831 94.5 2,725
Remarks: compressed load; dia: .375"; col: 3.580"; 53,600 cup
285 Speer GSSP Hodgdon H-4350 86.5 2,734
Remarks: compressed load; dia: .375"; col: 3.580"; 53,400 cup
285 Speer GSSP Hodgdon H-414 87.0 2,736
Remarks: dia: .375"; col: 3.580"; 51,700 cup
285 Speer GSSP Hodgdon H-380 76.5 2,561
Remarks: dia: .375"; col: 3.580"; 52,500 cup
300 Swift SP Hodgdon H-4831 93.0 2,649
Remarks: compressed load; dia: .375"; col: 3.560"; 54,200 cup
300 Swift SP Hodgdon H-4350 85.0 2,642
Remarks: dia: .375"; col: 3.560"; 53,500 cup
300 Swift SP Hodgdon H-414 84.0 2,623
Remarks: dia: .375"; col: 3.560"; 52,700 cup
300 Swift SP Hodgdon H-380 75.0 2,458
Remarks: dia: .375"; col: 3.560"; 52,500 cup

As to miking the web diameter to measure growth......IMO .001 growth is excessive......but I've quit measuring that.....I now try seating new primers.....You know quickly by the feel if they are not seating firmly.....and if not you're over the pressure you ought to be.

All other pressure indicators apply.....sticky bolt lift, flat primers, volcano'd primers.....but the acid test I now go by is the primer seating test.....if you have stretched the primer pocket.....back off!!! I'd say at least two grains.

That's not the best way to measure pressure .I remember one test that showed minimal expansion but when he sent it to a lab it was IIRC 75,000 psi !! Norma at one time addressed this problem and made brass so that it would show definite signs of expansion at the max pressures [ that brass is marked 'Re' on the headstamp]. Unfortunately there were those who thought the 'Re' meant it had been reloaded, and those who thought the brass far too soft since they had been loading to very excessive pressures !!! Web expansion is far from being scientific.

The other thing is that the "before and after" measurments only show you how sloppy your chamber is, and have nothing to do with pressure.
What you need to measure is the "after" from a factory load or a mild book load, and use that number to compare to the "after" measurment of your load. BTW, you have to do this on brass that has been fired less than 3 times or else the work hardining (from expansion/sizing) will throw off your results.
The brass expands to fill the chamber, and than relaxes slightly when the pressure is removed. A "hot" load causes more perminent deformation / less relaxing so it measures slightly larger than the "mild" load does. If you have a 0-1" mic that reads directly in "tenths" than you will be able to more accuratly measure this expansion, don't even try it with a caliper and even a .001 mic will yeild questionable results. Of course I won't even mention the amount of practice it takes to be able to measure "tenths" accurately with any amount of consistantsey.

quote:

Originally posted by vapodog:
As to miking the web diameter to measure growth......IMO .001 growth is excessive......but I've quit measuring that.....I now try seating new primers.....You know quickly by the feel if they are not seating firmly.....and if not you're over the pressure you ought to be.

All other pressure indicators apply.....sticky bolt lift, flat primers, volcano'd primers.....but the acid test I now go by is the primer seating test.....if you have stretched the primer pocket.....back off!!! I'd say at least two grains.

First of all........thanks for the ton of load recipes!! I know what you're talking about on the primer seating......kinda that "crunch" or whatever you want to call it when the new primer seats. Let me ask.....am I wrong in assuming that if you did not feel the crisp seating (meaning a sloppy pocket)....would not that round show primer flow back around the pin strike (volcanoing) after firing??

quote:

Originally posted by Strut10:
I've got a couple instances where I really think I need to understand, fully, the web expansion method to recognizing high pressures. Problem is......I'm not real well versed in what I need to be looking for...

Hey Strut10, Send me a PM with your email address and I'll send you a couple of Files.

One is on Case Head Expansion(CHE) and Pressure Ring Expansion(PRE). It is written in "Word".

And you will benefit from a Load Data Sheet which I have written in Excel.
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You will need a 0.0001" capable Micrometer to do the measureemnts. A 0.001" capable Micrometer just isn't accurate enough.

Since you are using the excellent Belted Cases, you will not need a Thin Blade Micrometer. The regular round anvil style will do just fine to measure both CHE and PRE.

If you can obtain one box of factory ammo, you can use it to establish your Benchmark Standard for PRE.

Once you begin using PRE and understand how it works, you will understand why it has been around since "Cartridge Style" firearms were introduced as the very best Pressure Detection Method available.

Best of luck to you.

quote:

You will need a 0.0001" capable Micrometer to do the measureemnts. A 0.001" capable Micrometer just isn't accurate enough.

Which is where the "head expansion" school of pressure measuring falls apart. It is simply not possible to accurately measure case head expansion as minutely as would be required to identify pressures approaching the capacity of the brass (which varies significantly with thickness and hardness). I've been hearing from guys for years who claim to be able to accurately measure .0002" of expansion, but the unevenness in the brass itself is often greater than this amount. To even begin to make this meaningful measurement you would have to measure the precised place on the case each time, not just the nominal dimension of the "round" head.

Vapodog has it down pat: When primer pockets expand enough to detect a difference in the firmness of seating a new primer, then you've exceeded the sustainable limits of the brass case. Beginning and end of story.

quote:

Originally posted by Stonecreek:
...To even begin to make this meaningful measurement you would have to measure the precised place on the case each time, not just the nominal dimension of the "round" head...

Hey Stonecreek, Surely you will not mind if I "agree" with you on that when doing CHE.

quote:

Originally posted by Stonecreek:
...Which is where the "head expansion" school of pressure measuring falls apart. It is simply not possible to accurately measure case head expansion as minutely as would be required to identify pressures approaching the capacity of the brass (which varies significantly with thickness and hardness). ...

And here I will disagree.

Good hunting and clean 1-shot kills.

Either loose primer pockets, or case head expansion indicate that the brass has been pushed to the yeild point. There is little additional strength left. This is the point to stop and think
about what you are doing.Even in a "sloppy" chamber
the case head will spring back if the pressure is normal.
Good luck!