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Originally Posted by Mule Deer
My understanding, from more than one major pressure lab, is that the 7mm RM shows a wider spread in pressures than most other cartridges of the same class, both high and low. Which is why the SAAMI Maximum Average Pressure (MAP) was set at around 60,000 PSI when piezo-electronic pressure-testing became standard.

Some other rounds have a SAAMI MAP of 65,000 PSI, which is as high as SAAMI will go, but they also have standard for what the highest-pressure round in a string measures, to allow a safety margin.


The same thing is reported with the 243 Winchester if I remember correctly?

Those are the two that you hear about anyway.

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Yep, but in the .243 the pressure variation apparently doesn't occur with bullets under about 100 grains.

One problem with both rounds (again, info from pressure labs) is the short neck and shoulder angle. The combination results in relatively quick throat erosion, which in its early stages can also result in erratic pressure. Once the erosion extends farther down the barrel, pressures tend to decrease.


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vapodog,

Do you have pressure-testing equipment?


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Originally Posted by Mule Deer
Yep, but in the .243 the pressure variation apparently doesn't occur with bullets under about 100 grains.

One problem with both rounds (again, info from pressure labs) is the short neck and shoulder angle. The combination results in relatively quick throat erosion, which in its early stages can also result in erratic pressure. Once the erosion extends farther down the barrel, pressures tend to decrease.




Thanks for the response. Wonder why you don't see the same thing in a 300 Win Mag despite a short neck and similar shoulder angle?

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My hunting load is 11 grains over max published by Hodgdon, but it with a moly bullet and 3.34" OAL, so it is more like 10 gr over max equivalent. There is still good safety margin to stay below extractor groove growth.

I have hunted with 3 bolt action 7mmRM rifles that I rebarreled, re stocked, re triggered, pillar bedded, rescoped, etc , and one Ruger #1 and one Browning 1885 that have original barrels.
I headspace at 0.215" to the belt, not the 0.220" minimum called out by SAAMI.


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Originally Posted by Clarkm
My hunting load is 11 grains over max published by Hodgdon, but it with a moly bullet and 3.34" OAL, so it is more like 10 gr over max equivalent. There is still good safety margin to stay below extractor groove growth.

I have hunted with 3 bolt action 7mmRM rifles that I rebarreled, re stocked, re triggered, pillar bedded, rescoped, etc , and one Ruger #1 and one Browning 1885 that have original barrels.
I headspace at 0.215" to the belt, not the 0.220" minimum called out by SAAMI.


Curious what velocity and what bullet your using if you don’t mind

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140 gr NBT 3400 fps


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Clark

I don’t doubt your results.

My oldest 7 Mag is a 700 from the late 80s, don’t remember exact yr.
it now is my Son’s but in my house.

I’ve shot pounds of the same powder and hundreds of 139s at 3300 FPS and
have had long case life - NO blown primers - no case head scrapes, etc.
The load is/was in a bullet manufacturer manual and in a book published
by a hunter, shooter, tester etc.
I shot that load for years in the SAME rifle so NO ONE can say it’s unsafe.
Any failures WOULD have shown up in SO many rounds fired.

ATST 3300 was my chosen velocity object and I did NOT attempt to push it
any harder or faster.

BTW it was very accurate too.

Jerry

Last edited by jwall; 11/18/19.

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All these tales of Uber Velocity and staying within SAAMI safe pressure limits makes me glad I have a couple of long necked 7mm Weatherby Magnums! LOL! Happy Trails


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One item to be duly noted is that the Remington factory ammo in 150 & 175 gr PSP Corelokts are Dual diameter bullets just like the 140 gr .264 by Remington used in their 264 Win Mag loads and their 140 gr 6.5 Creedmoor ammo. So from from cannelure back its groove dia and bore riding forward of the cannelure. MB


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