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Joined: May 2007
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Campfire Tracker
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Campfire Tracker
Joined: May 2007
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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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Joined: Jul 2001
Posts: 59,910
Campfire Kahuna
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Campfire Kahuna
Joined: Jul 2001
Posts: 59,910 |
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.
“Montana seems to me to be what a small boy would think Texas is like from hearing Texans.” John Steinbeck
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Joined: Jul 2001
Posts: 59,910
Campfire Kahuna
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Campfire Kahuna
Joined: Jul 2001
Posts: 59,910 |
vapodog,
Do you have pressure-testing equipment?
“Montana seems to me to be what a small boy would think Texas is like from hearing Texans.” John Steinbeck
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Joined: May 2007
Posts: 3,943
Campfire Tracker
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Campfire Tracker
Joined: May 2007
Posts: 3,943 |
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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Joined: Feb 2003
Posts: 10,324
Campfire Outfitter
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Campfire Outfitter
Joined: Feb 2003
Posts: 10,324 |
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.
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. -Ernest Hemingway The man who makes no mistakes does not usually make anything.-- Edward John Phelps
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Joined: May 2013
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Campfire Regular
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Campfire Regular
Joined: May 2013
Posts: 1,519 |
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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Joined: Feb 2003
Posts: 10,324
Campfire Outfitter
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Campfire Outfitter
Joined: Feb 2003
Posts: 10,324 |
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. -Ernest Hemingway The man who makes no mistakes does not usually make anything.-- Edward John Phelps
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Joined: Sep 2010
Posts: 19,179
Campfire Ranger
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Campfire Ranger
Joined: Sep 2010
Posts: 19,179 |
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.
jwall- *** 3100 guy***
A Flat Trajectory is Never a Handicap
Speed is Trajectory's Friend !!
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Campfire Tracker
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Campfire Tracker
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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
Life Member NRA, RMEF, American Legion, MAGA. Not necessarily in that order.
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Joined: Jan 2017
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Campfire Outfitter
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Campfire Outfitter
Joined: Jan 2017
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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
" Cheapest velocity in the world comes from a long barrel and I sure do like them. MB "
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