OK just for the sake of something to talk about. we have a post of going over max for a 308. now most books stop at a 50-55000 max pressure curve. (i know sometime its higher) but at the same time we have these short mags that come close to big case capabilities by running pressures to 65000. Now for the sake of argument, why can't we load a older round to the new rounds pressure even though its over the books max load?? and if that isn't safe, how come we are shooting short mags

Case design????

I believe some of us do. But the older cartridges of larger capacity seem to have enough velocity at their 'normal' pressures. Another considerations is the method of messurement used - piezo vs copper crusher. It makes the SSM's 'look' higher. (Just thinking out loud.)

quote:

why can't we load a older round to the new rounds pressure even though its over the books max load??

Check the ackley improved data!!!

In fact if we have a modern bolt rifle we can load to the 65,000 PSI....the trick is knowing when we are there....

I think the .270 Winchester is SAAMI spec'd at over 60,000 BTW....no reason why one can't load the .30-06 to the same pressures.....again in a modern bolt rifle!

Same for the 7 X 57 and 8X 57 and .280 Remington.....

Whether it is worth it remains a question to be answered by each individual reloader!

vapodog,

you beat me to it...
i was gonna ask,..." can you say ackley improved"?.
the short mags are very similar in theory, with the added short, fat powder charge

quote:

Originally posted by butchloc:
...at the same time we have these short mags that come close to big case capabilities by running pressures to 65000. Now for the sake of argument, why can't we load a older round to the new rounds pressure even though its over the books max load?? ...

Hey Butch, If you section one of the WSMs and compare it to a non-belted regular Case(308Win, 30-06 etc.), you will find the Internal Taper eminating from the Case Head is Thicker and extends farther toward the Case Mouth. When Winchester released that design, I applauded that excellent Feature "because" it will be used in the CRF M70s and eventually Mousers.

I know Butch understands why that is a benefit in the M70 design, but for the Beginners, the M70 CRFs and Mousers do not handle the Gas from Case Separations as well as about any Push Feed.

So, strengthening the Case in this critical location is an excellent way to increase the Safety Factor in these rifles a bit more.

Depending on the other Cases Internal Thickness at this same point(like Belted Mags) they might do just fine at a higher Pressure, but then Back Thrust is Higher due to the Case Head "Area" being larger than a 308Win or 30-06 size Case.

The Hardness of the Case Head can make all the speculation and guessing about increasing Pressure impossible.

Considering that the original owner of a "Used" firearm might have thought Exceeding MAX and High Pressure Loading is A-OK, are two of the main reasons I do not buy "Used" rifles.

Don`t get CUP and PSI piezo mixed up. Both systems are used and often in the same manuals or data pages on web sites.
The 308 and 30-06 are rated to 50,000 CUP which is equal to 60,000PSI the 270 Winchester is rated 52,000 CUP or 65000 PSI. These cartridges are loaded to almost the same levels. No commercial cartridge today is loaded over 65K psi piezo.
The older cartridges such as the 7x57 or 8x57 are loaded down due to so many rifles of unknown condition out there. They too, in a modern rifle, could be loaded to higher pressure if you have a way of accuratly determining the true pressures you are getting. Reading pimers or feeling for stiff extraction doesn`t tell you the pressure, a lab is usually needed.

It seems to me that most load manuals are conservative with listed max charges and optimistic with velocities for a given powder charge.

Over max on a cold day may be ok but brace yourself if it gets hot.

Here's the problem; load that .308W to 65,000 psi on a 60 degree day for the M700 and you're probably ok. Take it out on an 85+ degree day and you're not "ok". The .308W has a 60,000 psi Map which is why on 60 degree days it gives 54-56,000 psi. On 85 to 120 days it gives 60-65,000 psi and is safe. Most cartridges that have a MAP of 62-65,000 psi still only run 58-60,000 psi on 65-70 degree days.

Larry Gibson

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load that .308W to 65,000 psi on a 60 degree day for the M700 and you're probably ok. Take it out on an 85+ degree day and you're not "ok".

I cannot agree with this.
If you really have a 65,000 PSI load a few degrees will not be an issue.....even 25 degrees.....where one gets in trouble is when the ammo sits in the sun and the sun bakes it to the point of being too hot to handle!....or when shooting prairie dogs he allows the barrel to get hot and then chambers a round into a hot chamber and it heats to 150 degrees in the hot chamber before it is fired.

Mild temp changes alone have never been a problem for me!.....and I have loaded some hot rounds!

Vapodog

"Mild temp changes alone have never been a problem for me!.....and I have loaded some hot rounds!"

You have been lucky, that it hasn't happened to you does not mean it does not happen.. Many of us have had the problem and do not consider 85 to 120 degrees as "mild temp changes". Too many times I've seen .223 loads with H335 loaded to 60-62,000 psi on 60-70 degree days blow primers when shot on 85-90 degree days. The rounds were in magazines (bolt actions magazines not AR mags) and were not "laying in the sun". I've also seen the same with .243s, 25-06s, 270s and even a 7mm Magnum. Worst offender was a .220 swift loaded with 4064.

The SAAMI and CIP pressure MAPs do not mean that cartridges are loaded to that pressure. It means that under firing conditions up through 120 degrees (generally the top temperature during tests) the MEV does not excede the MPLM (the actual pressure for which the firearm should be designed).

Larry Gibson

Surely a "mild temperature change" is significant because of the resulting change in the barrel temperature which is going to be a lot greater. On a cool day, steel remains cold to the touch, on a warm day, steel gets too hot to touch, both from the sun and from firing, or both.

quote:

Originally posted by Larry Gibson:
...Many of us have had the problem and do not consider 85 to 120 degrees as "mild temp changes".

Hey doughnut eater, I've ZERO desire to argue with you, just going to provide some additional info for anyone interested to "chew".

quote:

Too many times I've seen .223 loads with H335 loaded to 60-62,000 psi on 60-70 degree days blow primers when shot on 85-90 degree days. The rounds were in magazines (bolt actions magazines not AR mags) and were not "laying in the sun".

I used to use a good bit of H335 then went to WW-748 and/or Bl-C2. Migrated to H4895 and H322. Now using Benchmark. All Loads were what I considered a Safe MAX as determined by the very best Pressure Detection Methods available to mankind - good old CHE/PRE.

I doubt I shot any of my 223Rem Loads below 45-50deg, but some of the Spring mornings at the Range were cooler than I liked. Top end temp might have been around a balmy 100-110deg during late July or early August in the SC Lowcountry. Don't believe I had a 223Rem in my hand later in August when it finally warmed up.

I do not remember ever Blowing a (Rifle) Primer with any of those Loads. Really sounds like the doughnut eater Pressure Detection Method is - full of beans.

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I've seen .223 loads with H335 loaded to 60-62,000 psi

Hodgdon's website shows no loads for the .223 over 54,000 PSI.....I suppose if one loads his .223 to 62,000 PSI he's going to be in trouble whether or not the temp rises.

quote:

Originally posted by vapodog:

quote:

I've seen .223 loads with H335 loaded to 60-62,000 psi

Hodgdon's website shows no loads for the .223 over 54,000 PSI.....I suppose if one loads his .223 to 62,000 PSI he's going to be in trouble whether or not the temp rises.

Vapodog

Probably because that is the MAP (Maximum Average Pressure...note the word "average") not the Maximum Allowable Pressure which many, including apparently you, think MAP stands for. The maximum average is less than the maximum allowable.

Also the SAAMI MAP for the .223 is 55,000 psi. The aximum allowable psi for the 5.56 NATO (using the same pressure measuring method) is 62,000 psi. Of course the MAP for 5.56 NATO is less. The lower MAPs allow for the rise in pressure from increased temperatures so that the the psi's are not "over the top" in extremely hot climates.

Larry Gibson

Hot Core

No argument at all. You used "good old CHE/PRE" so obviously the pressures weren't what you thought they were. In that they were safe loads within the temperature range you used them in. Obviously you enjoy rolling on the floor laughing you ass off at your self. That strikes me as strange since you were actually using something safe for once. Glad we could agree and not argue even though your usual snide comments denegrate from your otherwise intelligent conversation

Larry Gibson

While I can see varied opinions on temp verses pressure here, I can attest to the fact that it can and does happen, and also can be attributed to changes in atmospheric pressure and humidity as well.

I have experienced it with several powders, and in various calibers, both in my own loads and rifles and while in the company of other competent loaders.

Here is a case in point, the pictured cases, are from the same batch of powder, same batch of bullets, primers, and cases. All were loaded at the same time, only differences were the conditions at the time they were fired. The first 20 or so were fired in very low humidity, with temps in the mid 60's with the barometer reading low for our area. There were no issues with flattened primers, case head expansion, or extraction issues.

The cases pictured were fired in high humidity, and temps in the mid 80's and high readings on the barometer. As you can see not only were the primers ironed out across the head, but the case head actually flattened out almost erasing the stamped letters. There was also enough bolt tension that we had to use a wood block to remove these cases from the chamber.


Nothing else changed except the temp and pressure. The loads were not exposed to heat other than ambiant air temp as we were in the shaded end of a 60 x 100 barn. The rifle was the same temp as the ammo.

Two powders I know have this issue in our area are RL-25, and IMR-3031, depending on the load and rifle used. Still in all it has happened enough to know in my mind it is not a fluke caused by other issues.

I don't have a dog any any fight here but did want to point out that some here are not representing across the spectrum data, and that other issues do contribute to high pressure other than simply loading to max levels. In fact the loads pictured are the same load that the rifle was test fired with, zeroed with and over 100 cases fire formed with. The difference was however the temps and pressures changing between the firings.

Sense this time the loads have been adjusted and everything is wonderful. It shoots great groups out at 500yds even further when the conditions allow.

quote:

Hodgdon's website shows no loads for the .223 over 54,000 PSI.....

Now we know why!