Question about Chamber pressure

death-junky

death-junky

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My quick question why is the chamber pressure for modern cartridges different in the same rifle action. Like why is the 300 win mag max chamber pressure 64000psi and the 270 Winchester at 65000 psi?
 
The chamber pressures are established by organizations like SAAMI in USA or by C.I.P. in Europe. Not set by the rifle manufacturers. What arms get made or what ammo is loaded to must comply with CIP in Europe (is actually a law in many European countries) - but, SAAMI is completely voluntary in USA - no legal penalty for non-compliance.

In your example - likely very same rifle chambered in 30-06 - look up it's pressure rating set by SAAMI or CIP - is even lower... Besides chamber pressure, also have to consider "bolt thrust" - so same pressure with larger head size creates greater "bolt thrust" - sort of...
 
Now that answers my question a bit. The 300 win mag would have a larger cartridge face then say a 270 or 30/06. So yes physics dictate that there would be more overall thrust on the bolt. But then why is the 270 Winchester have a higher pressure rating then a 30/06? I ask this now because a 270 is essentially a 30/06 necked down and all the other dimensions are the same. These ratings to me look like they are just throwing darts at a board and pulling a number from there.
 
Possible firearm design basis differences - material properties different at time of inception (30-06 older cartridge), test action type, design factor variations,...so that factory ammo functions safely in all firearms chambered in whatever round.
 
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yeah interesting.
We mention how Ruger 1s can withstand higher pressure in Cals like 303... or say the 30-30 ! examples.
rifles tho, they arnt the 'same' rifles though often diffeent sized metals an actions, which as above must play part in limits? maybe.

and or the averages of that threaded barrel, those lugs in that position, with those forend bed screws, means that within the highest ### rating , the gun will still work an not kill the shooter by blowing up.. an then everything else under this is assumed. i dunno but following.
 
45-70 well known example factory ammo held to lower pressure for safe use in any modern 45-70 rifle. Reloading manuals typically list 3 pressure levels: Trapdoor, modern lever and bolt-action/Ruger No.1.
 
Typically, oldest cartridges had lower pressure ratings - kinda went with the actions of the day - for example, 7x57 in an 1893 Spanish Mauser. As time progressed, able to build stronger actions, stronger cases - 1903 Springfield rifle shooting 30 caliber 1906 cartridges (30-06). Ultimately, highest end stuff made recently - that 277 Fury mentioned above - not finding any factories chambering that one in 1896. And then was pure "silliness" - look at PSI and CUP limits for the 7.92 Mauser - CIP calls the cartridge an 8x57. SAAMI, apparently concerned that the bullet size was changed during its history, and that USA shooters were too "dumb" to know the difference between a "J" bore and a "S" bore, and would put the big diameter bullet into a smaller bored rifle, so, re-named the cartridge as "8mm Mauser" and set pressure limit very low, so could "get away' with "S" ammo in a "J" rifle. C.I.P., meanwhile, seems to assume the European shooters can read the designation on the ammo box and on the rifle, and know the difference between "J" and "S" bore, and therefore set much higher pressure limits - hence a European CIP 8x57 round is as much as 200 fps faster, than the equivalent weight of a SAAMI 8mm Mauser.
 
The 270 vs 39-06 chamber pressure discussion is one I’ve had. I actually have a chart somewhere for max 30-06 loads using the 270 chamber pressure limits. Makes a guy wonder when the 2 calibers are in identical rifles, eh? I always follow all the rules, of course...
 
I just googled it under images. It’s there. With a 26” barrel that one table referenced 2900-3000 with a 180gr depending on powder choice. My guess is the 270 was released with 65K as the spec so it could be better for marketing, and there were no old rifles around in that chambering that would be stressed.
 
death-junky said:
Now that answers my question a bit. The 300 win mag would have a larger cartridge face then say a 270 or 30/06. So yes physics dictate that there would be more overall thrust on the bolt. But then why is the 270 Winchester have a higher pressure rating then a 30/06? I ask this now because a 270 is essentially a 30/06 necked down and all the other dimensions are the same. These ratings to me look like they are just throwing darts at a board and pulling a number from there.
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Theres a lot that goes into max pressures. Others have mentioned the fact that older cartridges tend to have lower pressures, but thats only one reason. For instance, there are a bunch of newer cartridges designed for the AR15 rifle that have lower pressures due to the limitation of the action (6.5 grendel is spec'd at 52k psi, and 450 Bushmaster only 38.5k), these rounds use cases that are bigger (in diameter) than 556, and the bigger cases produce too much bolt thrust to safely operate in a standard AR15 at 556 pressure levels.

However, there is no reason you couldn't load these rounds at higher pressures in the correct rifle. Take the 6.5x55, in a modern Tikka rifle that round can be safely loaded to pressures over 60k, despite having a saami spec of 51k psi. I can only assume the same could be said about the Ruger Ranch Rifles in 450 Bushmaster - factory ammo will be limited to pressures that allow safe and reliable operation in a AR15, but I see no reason why hand loads couldn't be made with significantly higher pressures if you're using a modern bolt action.
 
emerson said:
The 270 vs 39-06 chamber pressure discussion is one I’ve had. I actually have a chart somewhere for max 30-06 loads using the 270 chamber pressure limits. Makes a guy wonder when the 2 calibers are in identical rifles, eh? I always follow all the rules, of course...
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I have read articles in Handloader magazine about exactly that. So take a rifle like a Parker Hale Safari - built on a commercial Mauser 98 action, or a Remington 700 - why would different pressure limits exist for 270 Win, 30-06, 9.3x62, and 7x57, when all made in the same rifle? Take a 30-06 case (or a 30-03 case) and form it into any of those others. Makes no sense, except, same articles shows testing results at pressure lab for Western Powders - almost all conventional home hand loader "signs" of pressure are not reliable / not dependable - sometimes do work, and sometimes do not work - not primer condition, not bolt lift, not case head expansion. Does not match up with actual pressure tests with strain gauges or pressure barrels. The only home hand loader "sign" that jived completely with "real" pressure testing data was muzzle velocity. No way to get more velocity with same powder, except by increasing pressure.

So, without a strain gauge setup, or pressure barrels, home guys like us pretty much need to stay with published information that was pressure tested. And note all the things we change in the recipe - different case brand, different primer, often different bullet. So, we are almost "on our own" when hand loading and not following the "book"...
 
Suther said:
Theres a lot that goes into max pressures. Others have mentioned the fact that older cartridges tend to have lower pressures, but thats only one reason. For instance, there are a bunch of newer cartridges designed for the AR15 rifle that have lower pressures due to the limitation of the action (6.5 grendel is spec'd at 52k psi, and 450 Bushmaster only 38.5k), these rounds use cases that are bigger (in diameter) than 556, and the bigger cases produce too much bolt thrust to safely operate in a standard AR15 at 556 pressure levels.

However, there is no reason you couldn't load these rounds at higher pressures in the correct rifle. Take the 6.5x55, in a modern Tikka rifle that round can be safely loaded to pressures over 60k, despite having a saami spec of 51k psi. I can only assume the same could be said about the Ruger Ranch Rifles in 450 Bushmaster - factory ammo will be limited to pressures that allow safe and reliable operation in a AR15, but I see no reason why hand loads couldn't be made with significantly higher pressures if you're using a modern bolt action.
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There is a MAIN reason not to load to higher pressures - you have absolutely no way to know what that pressure is.
Pressures testing is not a dart game..it’s done with lab equipment with known components. Thats why you have reloading data.
Hot rodding cartridges is a sure way to put someone safety on the block. Too many guys reloading think they know better than guns and components manufacturers who have the proper equipment of professionals to do the testing.

There is already data out for AR - semis and bolt gun. There is even specific load data for 7.62/.308 for gas gun like the M1A. You have it on a table. Just do your research.


We never had so much cartridge choices. If one caliber is not to your expectation..change for one that will do, in a gun and barrel made for that.
 
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Janeau said:
There is a MAIN reason not to load to higher pressures - you have absolutely no way to know what that pressure is.
Pressures testing is not a dart game..it’s done with lab equipment with known components. Thats why you have reloading data.
Hot rodding cartridges is a sure way to put someone safety on the block. Too many guys reloading think they know better than guns and components manufacturers who have the proper equipment of professionals to do the testing.


We never had so much cartridge choices. If one caliber is not to your expectation..change for one that will do, in a gun and barrel made for that.
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There are plenty of ways to know if you're in safe territory - QuickLoad, measured velocity, pressure signs on the cases... Will you know THE EXACT pressure, like you would with the required lab equipment? No. But you can still have a pretty good idea of whether you've cooked up a safe load or not.

Obviously this sort of thing is not for a total newb, but for some experienced handloaders going off the book is part of the enjoyment of it all. Case in point - Elmer Keith. Rather than sticking to the books, he wrote new ones!
 
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Janeau said:
...

We never had so much cartridge choices. If one caliber is not to your expectation..change for one that will do, in a gun and barrel made for that.
Click to expand...

About the best quote ever!!! In a Regina, Sask. gun shop, had a fellow bragging how he could get "damn near" 458 Win Mag performance from his Ruger #3 in 45-70 - struck me as odd - why not just get a 458 Win Mag? And it continued. Why push and hot load a 308 Win - just get same rifle in a 30-06. Or a 308 Norma Mag. Or a 300 Win Mag. Or a 300 Weatherby. At some point, maybe it is the 180 grain bullet that is not enough - so go up in caliber - 8mm Rem Mag, 338 Win Mag, 358 Norma Mag, 375 H&H, and so on. No reason to "push" or "red line" cartridges - just get one that does what you want, in its normal performance range. Take your boring old 30-06 and screw on a 9.3x62 barrel and tell me how boring that has become - same rifle, same receiver, same magazine - except "more" with 250 and 286 grain bullets...
 
Potashminer said:
About the best quote ever!!! In a Regina, Sask. gun shop, had a fellow bragging how he could get "damn near" 458 Win Mag performance from his Ruger #3 in 45-70 - struck me as odd - why not just get a 458 Win Mag? And it continued. Why push and hot load a 308 Win - just get same rifle in a 30-06. Or a 308 Norma Mag. Or a 300 Win Mag. Or a 300 Weatherby. At some point, maybe it is the 180 grain bullet that is not enough - so go up in caliber - 8mm Rem Mag, 338 Win Mag, 358 Norma Mag, 375 H&H, and so on. No reason to "push" or "red line" cartridges - just get one that does what you want, in its normal performance range. Take your boring old 30-06 and screw on a 9.3x62 barrel and tell me how boring that has become - same rifle, same receiver, same magazine - except "more" with 250 and 286 grain bullets...
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So true, and since you have brought up the 9.3X62, I was speaking with a fellow just a few hours ago and the discussion turned to 285 gr bullets loaded to over 2500 fps.

Yes, I have done that safely and with reasonable case life. It is however interesting that the original factory loading was that bullet loafing out of the muzzle at around 2150 fps. Otto Bock was the gunmaker who designed the cartridge to be used in 98 Mauser action rifles, all of which could easily have handled much higher pressure. That load is what the sterling reputation of the 9.3X62 was built upon, and it became the 30-30 of Africa.

Even though capable of much higher velocities in those rifles, it proved adequate for any game in Africa. It was not until sometime after WW1 that the factory velocity was increased by 200 fps to the current 2360.

The lesson is that the reach for that extra 100 fps or so, is not always wise nor satisfying, other than looking at a velocity screen or computer printout. Personally, I have settled on and been quite satisfied with the 285 gr at 2300 for the last four decades.

Ted
 
Back in the early days, cartridges were often proprietary designs by gun manufacturers that designed the cartridge around a specific gun or action. It was the gun that determined the pressure limit for the cartridge. Once the limit was established, it tended to stay at that level due to the guns that were in circulation. Sure, you can uprate a load for a 6.5 X 55, or a 7 X 57 in a modern action, the question becomes how much? Its not like they publish over-loads, and as above, visual signs that handloaders use can be very misleading.
 
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