Old data for 7mm RM
- Thread starter 1899
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- Golden Lake
My older Hornady manuals don't show pressure figures, however, I have a 1986 Hodgdon manual that shows loads for the 7MM Rem Mag varying from 46,800 CUP (139 gr bullet with 79 grs H870) to 55,500 CUP (154-162 gr bullet with 55 grs H380).
My 1987 Speer manual says that their data does not exceed the SAAMI average pressure limit of 52.000 CUP.
My 1987 Speer manual says that their data does not exceed the SAAMI average pressure limit of 52.000 CUP.
Thanks - I suspected that the max pressure had been significantly lowered at some point. I have a few older manuals but they don't show any pressures. Presently it is 61,000 psi (52,000 cup) compared to your old manual which shows 55,500 cup - although I don't know what that is in PSI.
Interestingly the .22-250, 6mm Rem, .270 Win, 7mm Weatherby, .300 Wby, .416 RM and 8mm RM are all 65,000psi.
The .264 Win Mag, .300 Win Mag and .338 Win Mag are all 64,000 psi
The 6.5mm RM and the .350 RM are both 56,200cup.
Interestingly the .22-250, 6mm Rem, .270 Win, 7mm Weatherby, .300 Wby, .416 RM and 8mm RM are all 65,000psi.
The .264 Win Mag, .300 Win Mag and .338 Win Mag are all 64,000 psi
The 6.5mm RM and the .350 RM are both 56,200cup.
You do realize that the reason so many old pet loads were reduced is that the 7 Rem Mag is prone to pressure spikes,(+20% or more) and if the spikes exceed the SAAMI standard of 52,000CUP (never has changed BTW) the loads are adjusted so the spikes stay below the max.
All this thanks to actual pressure trace technology.
Another tid bit is over time the relative burn rate of many powders do change.
The old H4831 is slower than todays ADI manuf'd H4831.
Use modern data for modern powders.
All this thanks to actual pressure trace technology.
Another tid bit is over time the relative burn rate of many powders do change.
The old H4831 is slower than todays ADI manuf'd H4831.
Use modern data for modern powders.
No, I have not heard of this, and it is difficult to believe. Why would this not happen in the .264 Win Mag or the .308 Norma Mag, both of which are very similar cases?
The other issue - that of new powders sometimes having different burn rates - I am aware of.
Also, why does the old quoted data give a 55,500 cup load if the SAAMI specs were always 52,000 cup max?
Doubt it all you want it is out there.
http://www.24hourcampfire.com/ubbthreads/ubbthreads.php/topics/3444038/1
http://www.leverguns.com/articles/saami_pressures.htm
http://thefiringline.com/forums/archive/index.php?t-402839.html
FWIW my number 11 Speer manual (1987) shows a SAAMI spec max pressure of 52000CUP, even though my Hodgdon manual No 24 (1983) does indeed show some loads in the 55000 relm, as does my No 25 Hodgdon of 1986.
The fact remains the 7mm Rem Mag has a deserved reputation, although the advent of affordable chrnographs, and modern pressure trace equiptment has shown it is'nt as wondorous as once advertised.
A few years back I invited 5 gentlement to share a chronographing session with me at the range, all 5 gentlemen had factory 24" bbl'd 7mm Rem Mags.
All done at -5 Celcius
All 5 rifles showed very similar results when factory ammo was chrono'd.
150's averaged 2950fps, 175's averaged 2700fps. suprisingly the fastest to slowest barrels were only on averaged about 25-30fps apart.
My chronograph has been proofed against other chrono's and validated versus ballistic software, and a known and proven load was shot over the screens both before and after the session to ensure things stayed very constant.
I conclude that the factories have noted the issue of pressure fluctuations, and even Speer mentions it in manuals going back as far as 1987.
As quoted from Speer #14 manual.
"Seldom will either handloads or factory ammunition match nominal factory ballistics in a sporting rifle and there is a great deal of velocity variation among sporters in this caliber. Rifles in Speer lab's collection posted velocities varying from 400fps under to 300fps over those posted by a SAAMI pressure barrel with the same ammo. because of this we have departed from our usual policy of showing velocities from a sporter. The velocities for the 7mm Rem mag are from a 24" pressure barrel."
The truth is the 7RM suffers from pressure spikes, as do a host of other popular cartridges.
http://www.24hourcampfire.com/ubbthreads/ubbthreads.php/topics/3444038/1
http://www.leverguns.com/articles/saami_pressures.htm
http://thefiringline.com/forums/archive/index.php?t-402839.html
FWIW my number 11 Speer manual (1987) shows a SAAMI spec max pressure of 52000CUP, even though my Hodgdon manual No 24 (1983) does indeed show some loads in the 55000 relm, as does my No 25 Hodgdon of 1986.
The fact remains the 7mm Rem Mag has a deserved reputation, although the advent of affordable chrnographs, and modern pressure trace equiptment has shown it is'nt as wondorous as once advertised.
A few years back I invited 5 gentlement to share a chronographing session with me at the range, all 5 gentlemen had factory 24" bbl'd 7mm Rem Mags.
All done at -5 Celcius
All 5 rifles showed very similar results when factory ammo was chrono'd.
150's averaged 2950fps, 175's averaged 2700fps. suprisingly the fastest to slowest barrels were only on averaged about 25-30fps apart.
My chronograph has been proofed against other chrono's and validated versus ballistic software, and a known and proven load was shot over the screens both before and after the session to ensure things stayed very constant.
I conclude that the factories have noted the issue of pressure fluctuations, and even Speer mentions it in manuals going back as far as 1987.
As quoted from Speer #14 manual.
"Seldom will either handloads or factory ammunition match nominal factory ballistics in a sporting rifle and there is a great deal of velocity variation among sporters in this caliber. Rifles in Speer lab's collection posted velocities varying from 400fps under to 300fps over those posted by a SAAMI pressure barrel with the same ammo. because of this we have departed from our usual policy of showing velocities from a sporter. The velocities for the 7mm Rem mag are from a 24" pressure barrel."
The truth is the 7RM suffers from pressure spikes, as do a host of other popular cartridges.
My old Lyman 23rd Edition book shows 52,800 CUP with some powders with max loads. None at 55,500 CUP.
"...don't know what that is in PSI..." There is no formula for converting CUP to PSI or the reverse. Two totally different ways of measuring pressure.
However, the manuals don't give SAAMI max pressures. Just the pressures obtained with a specific powder using a specific load.
"...don't know what that is in PSI..." There is no formula for converting CUP to PSI or the reverse. Two totally different ways of measuring pressure.
However, the manuals don't give SAAMI max pressures. Just the pressures obtained with a specific powder using a specific load.
10% more velocity = 20% more energy = 20% more pressure
10% more velocity = 20% more energy = 20% more pressure (for a given powder)
SAAMI specs 1992 rifles
-----------------------
You can find the SAAMI specs for many cartridges on
http://www.saami.org/specifications_and_information/index.cfm?page=ANSI
On pressure and velocities
-------------------------
Let me put it this way: I trust SAAMI, Lyman, Hodgdon powder data and Sierra.
I've found Barnes, Hornady and Nosler to be "optimistic" and sometimes off the chart!
As for hotter pet loads, many of them are borderline or even simply dangerous: for a given case capacity and maximum pressure there is only so much that is physically possible.
Remember this rule of thumb well:
10% more pressure = 10% more kinetic energy = only 5% more muzzle velocity.
20% more pressure = 20% more kinetic energy = only 10% more muzzle velocity.
As an example, Reloaders where driving 140gr 7 STW 300fps faster than any commercial loads and there was a good reason: the loads were running at well over 70 000 PSI!!!
This means that increasing muzzle from 3200fps to 3500fps (10%) means that chamber pressure increased by 20% (for a given powder)!
Alex
10% more velocity = 20% more energy = 20% more pressure (for a given powder)
SAAMI specs 1992 rifles
-----------------------
You can find the SAAMI specs for many cartridges on
http://www.saami.org/specifications_and_information/index.cfm?page=ANSI
On pressure and velocities
-------------------------
Let me put it this way: I trust SAAMI, Lyman, Hodgdon powder data and Sierra.
I've found Barnes, Hornady and Nosler to be "optimistic" and sometimes off the chart!
As for hotter pet loads, many of them are borderline or even simply dangerous: for a given case capacity and maximum pressure there is only so much that is physically possible.
Remember this rule of thumb well:
10% more pressure = 10% more kinetic energy = only 5% more muzzle velocity.
20% more pressure = 20% more kinetic energy = only 10% more muzzle velocity.
As an example, Reloaders where driving 140gr 7 STW 300fps faster than any commercial loads and there was a good reason: the loads were running at well over 70 000 PSI!!!
This means that increasing muzzle from 3200fps to 3500fps (10%) means that chamber pressure increased by 20% (for a given powder)!
Alex
- Location
- Golden Lake
There must be something about the 7MM Remington Magnum. The 1987 Speer manual I quoted has a boxed note which says: "We have been criticized for showing such low velocity with the 7MM Remington Magnum. Pressures were rechecked in a 2nd pressure barrel and velocities were checked in a minimum of 5 sporter rifles. The velocities shown are the best we could obtain.Higher velocities were obtained only by the use of non-typical hunting rifles."
Thanks for that first link; it had some interesting posts - especially the quote from John Barsness and the one by Flinch.
The answer seems to be that nobody knows why some 7mm RM loads have variations in pressure while others don't. I've loaded for it for 25 years and never had any problems.
The answer seems to be that nobody knows why some 7mm RM loads have variations in pressure while others don't. I've loaded for it for 25 years and never had any problems.
The SAAMI spec hasn't changed since the 7mm was first commercially loaded. The standard is approximately 60,000 psi.
The reason that older loading manuals show higher pressure loads than the newer manuals is that companies are more liability conscious now, not that the SAAMI standards have changed.
The reason that older loading manuals show higher pressure loads than the newer manuals is that companies are more liability conscious now, not that the SAAMI standards have changed.
Having done chamber casts on a number of 7mm Rem Mags, I am quite surprised at the large variance of dimensions I have run into.
This also would account for larger charges being shown in some older manuals, vs the newer ones. I believe as far back as Speer #8 this was noted.
While never experiencing any of the pressure "spikes" alluded to, I know that 7mm Rem Mag rifles require caution when working up loads.
My personal experience has given me the folloing criteria that I use:
160 grain bullets in a 24" barrel, around 3050 fps max,
150 grain bullets 3100 fps and pennies;
140 grainers, 3200 or so.
Regards, Eagleye.
This also would account for larger charges being shown in some older manuals, vs the newer ones. I believe as far back as Speer #8 this was noted.
While never experiencing any of the pressure "spikes" alluded to, I know that 7mm Rem Mag rifles require caution when working up loads.
My personal experience has given me the folloing criteria that I use:
160 grain bullets in a 24" barrel, around 3050 fps max,
150 grain bullets 3100 fps and pennies;
140 grainers, 3200 or so.
Regards, Eagleye.
