7MM WSM Pressure signs

[DKSDonnie]

I recently got back into reloading and started reloading for my WSM's. First, I have a Browning ABolt in 7MM WSM with a 23" barrel. I have read just about every post I can find on pressure signs. Some reloaders swear on the "Just forward of the extraction groove on the web" measurement, some swear by primer sign, some swear by bolt lift, some say watch your chrono speeds, some say watch it all, others believe in a couple signs and forget the rest. I'm going to watch it all. I have measured some factory Winchester Supreme casings that were never fired and at the web they measured .5485. I also have once fired in the same casings which measured at .5525 at the web. Now, from what I've read, you should see no more than .0005 and .0007 expansion with short mags. Hodgdon says to only measure new brass compared to once fired brass because measuring once is not accurate due to case hardening. Due to SAAMI specs, factory ammo is made to fit all rifles and if you have a larger chamber, you will have more growth than that. So I'm at .0040. Either the factory Winchester Supreme ammo is way over max or I have a larger than normal chamber or this expansion is normal when firing casings for the first time. Is Hodgdon is full of it? Should I be concerned? I've read where Winchester Supreme ammo for the WSM's is pretty much at Max loads. Hence the flattened primers which could be also caused by headspace on new brass. Some insight is much appreciated.

 

[Laphroaig]

I've never measured web expansion so I'm probably not the best one to answer, but all chambers are not cut the same so I can't see how your measurements will tell you anything.

Now I do pay attention to the other 3 parameters when working up loads. Primer flattening is a relative thing. The flatter the primer, the more pressure you're producing. Doesn't really indicate unsafe on its own. Chrono numbers are also a relative thing but do let you know where you stand if you have properly worked up your load. Hard bolt lift? You have crossed the line and need to back off.

I've read where Winchester Supreme ammo for the WSM's is pretty much at Max loads.

I've always thought that factory rifle hunting ammo for modern cartridges is loaded to Max, or nearly so. Ammo companies aren't competing with each other using starting loads. I recently bought some 270 WSM Federal 150 gr. partition ammo from Midway. It worked well from a M70 FWT. But check out the reviews. 3/10 reviewers reported over-pressure signs.

https://www.midwayusa.com/product/7...gnum-wsm-150-grain-nosler-partition-box-of-20

 

[243winxb]

Some reloaders swear on the "Just forward of the extraction groove on the web" measurement,

I think the place to measure is in the extractor groove? Any expansion may be to much, even as little as .0005" ?? This means the primer pockets may have expanded also?

I will admit , i never fully understood or had the correct micrometer to take measurements.

These cover some signs in rifle & handguns.

 

[DKSDonnie]

I've never measured web expansion so I'm probably not the best one to answer, but all chambers are not cut the same so I can't see how your measurements will tell you anything.

Now I do pay attention to the other 3 parameters when working up loads. Primer flattening is a relative thing. The flatter the primer, the more pressure you're producing. Doesn't really indicate unsafe on its own. Chrono numbers are also a relative thing but do let you know where you stand if you have properly worked up your load. Hard bolt lift? You have crossed the line and need to back off.



I've always thought that factory rifle hunting ammo for modern cartridges is loaded to Max, or nearly so. Ammo companies aren't competing with each other using starting loads. I recently bought some 270 WSM Federal 150 gr. partition ammo from Midway. It worked well from a M70 FWT. But check out the reviews. 3/10 reviewers reported over-pressure signs.

https://www.midwayusa.com/product/7...gnum-wsm-150-grain-nosler-partition-box-of-20

You and I pretty much think along the same lines. I have also read where WSM's owners have reported high pressure signs with factory ammo. I have an opinion for what it's worth. If you have overpressure signs, the first place they will show is at the areas of a casing that the pressure can escape first. that would be at the primer and at the mouth where the bullet leaves the casing. It takes hardly any effort to seat primers and bullets. The casing (after being fired once) is supported by the chamber. One would think you would see signs at the primer and higher than normal velocities if reaching overpressure. I'm sure that if you follow data put forth by the reloading books that you would be safe because they are not going to put out info on ammo that is going to be unsafe in any way. They don't want that lawsuit. One would would also think that after firing brass once, you wouldn't have the slamming effect of casings against the bolt face so bad which I've read that sometimes cause flat primers and gives you a false overpressure reading. Seems to be just too many variables when it comes to diff rifles and diff manufacturers of brass and components to truly say what is a tried and true way to measure pressure. I guess the ways we use and have been used by many reloaders for eons has worked and noone has ever been seriously hurt. Opinions differ widely among reloaders but it seems to work. By the way, I have both a 7MM WSM and a 270 WSM and both have flattened primers with a touch of cratering and the once in awhile stiff bolt on ejection with Winchester Supreme ammo.

 

[DKSDonnie]

I think the place to measure is in the extractor groove? Any expansion may be to much, even as little as .0005" ?? This means the primer pockets may have expanded also?

I will admit , i never fully understood or had the correct micrometer to take measurements.

These cover some signs in rifle & handguns.
View attachment 760993

Thank You sir! I think I will print this and use it as a step by step way of determining if they are safe loads or not. It could be a combination of a couple or all but if you follow these steps and determine what's causing these issues, you should be safe.

 

[243winxb]

The WSM and some other cartridge have a working maximum pressure of 65,000 PSI.

Olin had posted this at one time.

modulus of elasticity- Cartridge Brass-
Material is 70 copper/30 zinc with trace amounts of lead & iron , called C26000. Material starts to yield at 15,000 PSI when soft (annealed), and 63,000 PSI when hard.
Material yields, but continues to get stronger up to 47,000 PSI when soft, and 76,000 PSI
when work hardened. Modulus of Elasticity is 16,000,000 PSI. This means to pull a 1.000 inch long strip to 1.001 inch long induces a 16,000 PSI stress.
So if you pull a 1.000 inch strip to 1.005 inch long, you get about 76,000 PSI, which is the max obtainable.

Not sure what it all means? But i would guess the working pressures are right on the edge where brass may not spring back after firing. This would show up as sticky bolt lift and/or hard extraction of the fired brass?

 

[DKSDonnie]

So where would the number .0005 versus .005 show anything at all. Just trying to understand where the number of .0005 came from. Not questioning you of course. A human hair averages .004. Makes me think that if we are measuring down to .0005 to measure pressure signs to make sure we don't injure ourselves or someone else or worse, we shouldn't be reloading.

 

[243winxb]

The whole point is, its a useless measurement from what i have read. The .0005" can only be measured by an expert and when its expanded to .001" its to late, because the primer pocket has expanded also.

 

[Leatherstocking]

243win, lots of micrometers can measure to .0001, this involves a vernier scale in addition to the usual ones. I would not trust a digital mic to measure this accurately.

 

[243winxb]

243win, lots of micrometers can measure to .0001, this involves a vernier scale in addition to the usual ones. I would not trust a digital mic to measure this accurately.

We need a machinist to do some testing. Not I.

Did some googling. http://benchrest.com/showthread.php?65270-Case-head-expansion

Click the "Varmint Al " link.

 

[jmr40]

By the time pressure signs show up you are already waaay past where you should be. Buy a $100 chronograph. If the manual says the max load you are working on will be 3000 fps, you are at a max load at 3000 fps regardless of the powder charge. In most cases I find the manual pretty accurate, but with some powders I've reached a max load as much as 3 gr below the loading manual. At other times I've been right at the book max and still been 100-200 fps slow.

 

[DKSDonnie]

By the time pressure signs show up you are already waaay past where you should be. Buy a $100 chronograph. If the manual says the max load you are working on will be 3000 fps, you are at a max load at 3000 fps regardless of the powder charge. In most cases I find the manual pretty accurate, but with some powders I've reached a max load as much as 3 gr below the loading manual. At other times I've been right at the book max and still been 100-200 fps slow.

I agree. Pressure equals velocity!

 

[Blue68f100]

Here is a good link on how to read pressure signs. This was posted several years ago.

https://www.primalrights.com/library/articles/understanding-pressure

 

[DKSDonnie]

Here is a good link on how to read pressure signs. This was posted several years ago.

https://www.primalrights.com/library/articles/understanding-pressure

Great article. thanks for posting.