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Thread: Rifle Cartridge Pressures

  1. #1

    Default Rifle Cartridge Pressures

    Was wondering if someone can help explain pressures in rifle cartridge reloading. I have been comparing two similar rifle cartridges - 260 Remington and the trusty old 6.5x55. The load data I've seen comparing the same components in these produce near equal velocities with the small edge going to the 260. But the pressures between the two loads seem great - I think. Roughly 57K for the 260 Rem and 45K for the Swede according to the Hodgon data. Is this a substantial amount? Does it significantly put more stress on rifle (barrel erosion) and brass? Does it really matter? I would prefer sticking with the Swede but something new and different makes the 260 intriguing. Thanks in Advance.

  2. #2

    Default A major factor

    in allowable pressures is what firearm the cartridge will it be fired in. The older rifles that shoot the 6.5 X 55 can handle less pressure than newer rifles of stronger design and metals. The 6.5 X 55 in a modern firearm can be loaded to higher pressures. The 260 Rem is a modern cartridge made for use in strong actions, so it was always loaded to higher pressures than the original 6.5 X 55 loadings. It isn't really pressure that is hard on barrels, as long as pressures are kept within SAAMI specs, it is the amount of powder and what kind.

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    Default Pressures

    Older rifles were made of "weaker" metals then today and reloading has to take into account someone shooting a century old rifle.

    That said.... one can pack just so much powder into a case. Pressure exerted on the bullet during its time in the barrel is the amount of "work" performed by the system. A smaller case volume will need higher pressures to equal a larger case volume at a lower pressure to propel a bullet out the muzzle at the same velocity. Looking at the powders used... the Swede does well with slow magnum powders while the 260 needs faster powders to pack similar energy.

    As noted above... modern rifles can be loaded to higher pressures for all of the old calibers. The Swede has a superb reputation for accuracy and killing power. If you want a smaller action (308 class) to make a handier rifle, then the 260 is the ticket.

    There was an article on the new Les Baer 260 long range rifle in one of the gun mags. 10 shots, one hole at 100 yards.... and $3000 worth of rifle.

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    Richard Lee talks about pressure quite a bit in Modern Reloading 2nd edition.

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    Default Pressure factors

    Pressure is a function of 3 different factors and a couple of minor considerations. Bore dia., inside case volume, and quantity and speed of the burn of the powder used. Given that both cartridges have the same bore and can use the same powders the primary difference between the two is case volume. The Swede has a slightly larger volume which translates to a slight drop in generated pressure. The inside of the case acts like an expansion chamber. The larger the chamber the lower the pressure than can be generated for the same amount and type of powder given equal bore size. One can generate more pressure with less powder using a faster powder to the point you could blow up an action with a charge of a fast powder that would be OK in a different cartridge in the same action.

    Erosion is a combination of flame temperature and pressure. More pressure and fast burning powders makes your barrel maker and gunsmith grin The idea that an "over bore" cartridge causes throat erosion due to the amount of powder alone doesn't work. Think about it like heat and scrubbing. More heat and less pressure or more pressure and less heat has less effect on metal than more heat and more pressure. The way to save your barrel is to slow the powder burn rate down instead of using less of a faster powder.

    I would disagree that the older actions were made out of "weaker" metals. A Mauser 93, 94, 95 small ring action is weaker than a Mauser 98 large ring action not because there was a leap forward in metallurgy between 1895 & 1898 but due to the difference in design. Part of that design difference is in the increased amount of steel in the breach area and the way the case is supported. Not many will argue about the suitability of a 100 year old German pre-war M98 for most any modern cartridge one could stuff in it.

    In a "modern" action I would go for the Swede over the 260. Even with the fact that 260 cases can be made out of 308W cases and the Swede really can't be made without a lot of trouble out of anything the slightly larger case wins. That and the history of the 6.5-55. Newer isn't necessarily better it's just newer. As you indicated the velocity difference is not a factor in modern action loadings.

  6. #6

    Default

    Thanks for the great responses guys. I learned a great bit.

  7. #7

    Default cartridge comparison

    I was wondering the same thing between the 338-06 and its parent cartridge-the 30-06.
    The older hogdon manual I was reading listed the 338-06 10K psi greater then then '06. I thought they should be close do to the case.

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    Default Difference in pressure?

    Quote Originally Posted by green sourdough View Post
    I was wondering the same thing between the 338-06 and its parent cartridge-the 30-06.
    The older hogdon manual I was reading listed the 338-06 10K psi greater then then '06. I thought they should be close do to the case.
    First we need to know if the 06 was rated in C.U.P pressure or PSI pressure. Generally older cartridges are still listed from habit or lack of modern testing in CUP units. Newer cartridges are generally tested in new pressure barrels that read in PSI units. Not the same animal. Also there is not a direct way to convert between CUP and PSI. We are also assuming that you correctly listed PSI as the unit of measurement for the 338-06. For a given cartridge the PSI standard is generally higher than the older CUP standard. So first are we on apples to apples? The Speer # 13 I grabbed first listed the 30-06 at 50K CUP as the industry standard. Same book listed the 338-06 at 53K CUP so not much of a difference.

    The first problem is having 2 different standards. The reality is that CUP or PSI doesn't matter as long as you don't exceed ether type of pressure your action can handle safely. The industry standard for a given cartridge is set at a point where commercial cartridges are generally safe in any action their chambered for given the idea that the action is in good condition compared to what a new action of the same type would be. What you end up with is that different actions operate safely at different pressures for the same cartridge. 7mm Mauser for example. In a small ring 93 Mauser it is somewhat of a milk toast round. In a Rem 700 you can make it boogie along. Same case different pressures. Industry standard says you have to load commercial 7mm Mauser to milk toast standards or mark the box to indicate that the round in the box is not for older actions. Same with the 30-06. They can be pushed harder in a "modern" action. Don't put your hot hand loads in a M1 Garand. It will eat it for a while but it will not like it

    So the 30-06 given a good action could probably be pushed a little bit. The 338-06 is at the point where it may be tweaked a very little but is more likely to start pushing back. Both are good stuff.

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    Default

    A lot of good, and interesting info has been posted.

    I have 3, 7x57s. My 98 mauser, and my wife's Ruger 77 are strong actions, so I have no uneasiness about using a Max Load in either of them.

    My 95 Chilean Mauser has a weaker action, so I don't load it as hot.

    They are each different in throat length, though, and there are reasons, other than how hot the load, to consider. Of course, all rifles are unique. It's something that handloaders have to understand and deal with.

    For example, if I used the loads for the 95 that has a long throat, and are loaded for an OAL that fits the magazine,,,,, in my 98 with the new barrel, and shorter throat, they would be TOO LONG, and SEAT DEEPER when I chambered them. That could increase pressure a lot.

    Again, this is not unique to just the rifles I mentioned.

    We need to consider Action Strength, if we wanna be safe. I've seen these small ring mausers, 93s, 95s, and the like, chambered for 308 winchester, which is a modern cartridge that is loaded to higher pressures than those weaker actions are designed for.

    I'm pretty sure those actions don't have enough of a margin to be considered safe, with the 308, but I'm not an expert on the strengths of the various actions, like some of the people who frequent this forum.

    Smitty of the North
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    Default Smitty of the North

    You have exposed one of the weakness of this type of forum. The problem (problem may be the wrong word) is that someone asks a question about X. Someone else answers hopefully correctly. Then maybe others join in with opinion, fact or both. That is all good. As long as we learn something that is what we all started out to do. What we as posters sometimes loose sight of, and as readers get separated from, is the context of the original question. The best that I can tell everything you posted in your last post on this thread was and is true. What also is true is that every post is not necessarily a complete answer. We need to consider everything to be safe. Everything has to be considered in the original context of its design to be safe. The original question was about the pressure differential between two cartridges and what did the pressure difference mean. The answers expanded that narrow question some what. For example I only have 1 7x57 so all of my hand loads are unique to that action, barrel, cartridge combination. I have several 300 win mag's. Although they are built on the same manufacturers action each one is slightly different. So when I handload for each rifle the OAL is different for each with the same bullets. Not much but enough to make a difference in pressure if the longer OAL is used in the shorter chamber. That is OK for punching holes in paper. I can keep track of which load goes in which rifle no problem. When I take them to the field the field load is different in that the OAL is good for both so I don't have to remember which rifle needs which cartridge or have a pocket full of the wrong loads for the rifle I have with me. One example of something that can effect pressures. We never got into the potential problems of using Magnum versus standard primers, slow versus fast(er) powders, military versus commercial cases, different bullet weights & shapes and their effect on OAL. You touched on short chamber versus long free bore. Or what happens when you mix all of those factors together.

    Consider your Mauser 95 action. I used the 7X57 to illustrate the difference in capacity of the M95 and M98 actions only. Your 95 is still about as strong as the day it was made. From a cartridge pressure standpoint it was designed to handle less pressure than your Mauser 98. Does that make it weaker or does it just have less capacity to handle more pressure. Personally I think there is a difference between capacity and strength. Example of my thinking would be a preWW2 German M98 is about as strong as they come. Some of the same German M98's made in late 44-early 45 were close to junk in the strength department. Same "capacity" but different "strength" of materials, heat treat, care of manufacture. It's the same with the Spanish small ring Mausers that were armory re-barreled to 7.62x51 NATO. Are they safe? I have one that hasn't had a problem yet. would I run something other than low power NATO rounds in it? NO Would I recommend it to most people? NO Would I sell it to you? YES I think you could handle it understanding it's limitations.

    I post this not to cause any controversy about who is right or more right or wrong. I merely want to point out to readers that there is generally more information than is posted to consider when reading these posts about what ever subject the thread is about. Sometimes the context of the question is lost in the answers.

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    [QUOTE Sometimes the context of the question is lost in the answers.[/QUOTE]

    Well, the entire post was good and on topic, but the line above is golden, with respect to every thread on every board on every site on the www.. It's all information and entertainment, but no one should stake their well-being on anything that they 'learned' on the internet.

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