I know to be looking for pressure signs with reloading but I'm just wondering what the difference is between rifles that cause them to reach max loads at different levels. Ive read about some guys being able to safely push their rifles well above book max in order to get higher velocities. Is it differences in the chamber or is it in the brass and bullet combos or some of each. I'm not wanting to push anything too hard, I'm just wanting to educate myself more on reloading.
What causes pressure tolerances to be different?
- Thread starter Ed82
- Start date
Guys who load above max are taking a serious personal risk of damaging themselves and their rifles. Going over max isn't safe. Lot of 'em think the manufacturers are publishing data based on what the company lawyers tell 'em.
Rifles don't have max loads. They are designed and built to withstand pressures in a given range.
The best source of info is in the reference section of your manual. There is a great deal of really good info there. Partial to the Lyman book myself. Lots of good info in Hatcher's Notebook too.
A rifle's receiver type can be inherently strong or not so strong. A bolt action vs a rolling block, for example. The bolt action has a lot of steel and better steel than a rolling block behind the cartridge. Lot of that has to do with metallurgy. Steel is far different now than it was 100 plus years ago.
Rifles don't have max loads. They are designed and built to withstand pressures in a given range.
The best source of info is in the reference section of your manual. There is a great deal of really good info there. Partial to the Lyman book myself. Lots of good info in Hatcher's Notebook too.
A rifle's receiver type can be inherently strong or not so strong. A bolt action vs a rolling block, for example. The bolt action has a lot of steel and better steel than a rolling block behind the cartridge. Lot of that has to do with metallurgy. Steel is far different now than it was 100 plus years ago.
Primer type,
Crimp,
Bullet to first rifling land distance,
Temperature of the chamber,
Volume of powder in the round,
Brass brand name,
Bullet versus bore diameter,
Bullet weight,
Bullet design,
Bore cleanliness,
...... All affect pressure peak.
And since on a given day all of the variables can line up the wrong way, some safety factor is prudent. Going above max published is squandering the safety factor with increasing personal risk to gain a few fps. And remember that the fastest combination is seldom the most accurate, knocks you around more and wears your gun out.
Crimp,
Bullet to first rifling land distance,
Temperature of the chamber,
Volume of powder in the round,
Brass brand name,
Bullet versus bore diameter,
Bullet weight,
Bullet design,
Bore cleanliness,
...... All affect pressure peak.
And since on a given day all of the variables can line up the wrong way, some safety factor is prudent. Going above max published is squandering the safety factor with increasing personal risk to gain a few fps. And remember that the fastest combination is seldom the most accurate, knocks you around more and wears your gun out.
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sunray loading manuals are ball park estimates, I have a stock factory Savage .223 bolt action and the throat is longer than either of my AR15 rifles and can be loaded hotter than average .223 data. Not only is your statement false (and stupid) it also show you have very little experience working up loads and checking for pressure signs. Bottom line, find another hobby you know something about and stop spreading bovine scat in reloading forums.
Below is the same load of 25 grains of H335 in two different .223/5.56 cartridge cases that vary in 1.8 grains of H2O case capacity and the chamber pressure varies 6,000 psi. This is vivid proof you don't know what you are talking about and let alone read the front part of your reloading manuals trying to learn something worthwhile.
Guys like you sunray who shoot off their mouth without thinking take a serious personal risk of sticking their foot in their mouth and making a horses backside out of themselves.
Ed82
Below is an exaggerated example of case base expansion caused by over pressure, when working up loads you measure the base of the case and if the case expands .001 in diameter your pushing the brass too hard. "BUT" case brass hardness varies and this expansion is not a sign of a given pressure, it is a sign of reaching the limits of that type/brand of case meaning the strength of the brass.
Normally the first sign you will see is the brass in the base of the case flowing into the ejector in the bolt face.
Any time you see these signs or overly flattened primers its time to reduce the load to lower pressures.
Which max? You can look at three different manuals, all using identical components, and all three may have a different maximum load listed for that component combination. It's quite possible to exceed the max load listed in a manual, and actually produce less pressure that the firearm used in the manual, with the same powder charge. By the same token, just because a load is listed in a manual, doesn't mean that the load is safe in your rifle.
BigEd
I'm moderately aware of what I'm looking for as far as pressure signs go but that's good info and pictures on the ejector recess flow. I've searched for pictures of pressure signs online but I haven't seen any like that that showed the ejector flow. Most pictures I've found we're pretty vague and low clarity.
You mentioned the throat length affecting the pressure. How much does chamber tolerances affect pressure and on which direction? Would a factory Remington, with their typically long throat, be able to run a higher pressure than an aftermarket barrel cut with tighter tolerances (all other things being equal)?
I know the 7.62x51mm has a lower max pressure than .308win I would assume that's because of the looser chamber in the military rifles in order to allow them to function in dirtier conditions.
There's an article on 6mm benchrest about the .243 win where they talk to George Gardener about his tactical rifle set up and he talks about how he's pushing a 115gn. bullet at 3150 fps but in the manuals I've looked at the 105gn bullets are topping out under 2900. I'm not trying to get his velocities but at max load (after ladder test with no pressure signs) I was getting 2820 with my 105 hpbt's. It just got me wondering what effect different changes would make to my current set up. Guys talk about changing their seating depth and other stuff for fine tuning their accuracy I just don't know enough to know where to start. So I came here to learn
I'm moderately aware of what I'm looking for as far as pressure signs go but that's good info and pictures on the ejector recess flow. I've searched for pictures of pressure signs online but I haven't seen any like that that showed the ejector flow. Most pictures I've found we're pretty vague and low clarity.
You mentioned the throat length affecting the pressure. How much does chamber tolerances affect pressure and on which direction? Would a factory Remington, with their typically long throat, be able to run a higher pressure than an aftermarket barrel cut with tighter tolerances (all other things being equal)?
I know the 7.62x51mm has a lower max pressure than .308win I would assume that's because of the looser chamber in the military rifles in order to allow them to function in dirtier conditions.
There's an article on 6mm benchrest about the .243 win where they talk to George Gardener about his tactical rifle set up and he talks about how he's pushing a 115gn. bullet at 3150 fps but in the manuals I've looked at the 105gn bullets are topping out under 2900. I'm not trying to get his velocities but at max load (after ladder test with no pressure signs) I was getting 2820 with my 105 hpbt's. It just got me wondering what effect different changes would make to my current set up. Guys talk about changing their seating depth and other stuff for fine tuning their accuracy I just don't know enough to know where to start. So I came here to learn
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There are so many factors that contribute to pressure and pressure signs it would be hard to write about them all at once.
The easiest and best way to guesstimate pressure is with a chronograph and common sense. If you are getting 200 fps more than everyone else in comparable bbl lengths you are most likely running at a pressure over max. Same thing if you are seeing much lower velocities you are below max press.
Lots of guys will run very high pressures and feel fine about it because the brass looks good and the cases are easy to extract from the chamber. What they can't see the the cumulative metal fatigue taking place over time in their action. Guns are built to take pressure cycles numbering in the hundreds of thousands. When you increase the pressure the number of cycles the gun can take before stress cracking occurs decreases very rapidly.
As an example of this right now I am working on a project to replace pressure vessels which have exceeded the maximum pressure during pressure cycling. Normally these vessels are good for 900000 cycles but press was increased a very small amount during the pressure cycle. The number of cycles before stress cracking occurs had dropped from 900000 down to 20 cycles. That is with just an 11% increase in pressure To put in gun terms it would be like going from 65000psi to 72000psi. The kicker is that you may not see traditional pressure signs on your brass at 72000 psi!!!
The easiest and best way to guesstimate pressure is with a chronograph and common sense. If you are getting 200 fps more than everyone else in comparable bbl lengths you are most likely running at a pressure over max. Same thing if you are seeing much lower velocities you are below max press.
Lots of guys will run very high pressures and feel fine about it because the brass looks good and the cases are easy to extract from the chamber. What they can't see the the cumulative metal fatigue taking place over time in their action. Guns are built to take pressure cycles numbering in the hundreds of thousands. When you increase the pressure the number of cycles the gun can take before stress cracking occurs decreases very rapidly.
As an example of this right now I am working on a project to replace pressure vessels which have exceeded the maximum pressure during pressure cycling. Normally these vessels are good for 900000 cycles but press was increased a very small amount during the pressure cycle. The number of cycles before stress cracking occurs had dropped from 900000 down to 20 cycles. That is with just an 11% increase in pressure To put in gun terms it would be like going from 65000psi to 72000psi. The kicker is that you may not see traditional pressure signs on your brass at 72000 psi!!!
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Ed82
The European CIP the equivalent of the American SAAMI considers the .308 Win and 7.62 NATO to be the one in the same cartridge rated at the same chamber pressure and the same applies for the .223/5.56. Our SAAMI sets dimensional "guidelines" for chambers and throats "BUT" these guidelines are not written in stone.
A military chamber is approximately .002 larger in diameter with longer headspace settings and the diameter of the chamber can effect the pressure slightly because it affects case capacity. The throat has the greatest effect on chamber pressure along with seating depth. But I can safely jam my .223 bullets into the rifling as long as I work up the load and stop at the first signs of excess pressure.
I was very surprised to find out my Savage .223 with a 1 in 9 twist had a longer throat than my AR15 rifles. What I found out was .223 rifles with a 1 in 14 or 1 in 12 twist will have shorter throats and shooting lighter bullets so there are many variables. Weatherby rifles rifles are famous for their high velocities and they do this with longer throats, BUT you won't find them winning any benchrest competitions with these long bullet jumps.
Below are .308/7.62 chambers, look at the base diameter, freebore diameter, freebore length and freebore angle. The freebore or throat dimensions have the greatest effect on chamber pressure and they also vary with your seating depth.
Below is is very telling about factory loads and chamber pressure, the green bar on the far left is a factory loaded .223 cartridge fired in a .223 rifle. The .223 and 5.56 are both rated at 52,000 cup or 55,000 psi but the factory .223 was only loaded to just below 50,000 psi. "BUT" the military loaded 5.56 NATO round the blue bar on the far right was loaded to approximately 55,000 psi. The two middle blue and green bars show the pressure differences between a SAAMI throat and the longer military throat.
Bottom line, no two firearms are identical, I was shooting two .357 revolvers over the weekend with my son and by looking at the primers I could see the fired case fired in his Ruger were slightly flatter than my S&W. If you look in the Lyman reloading manual you will see loads fired in a universal receiver and pressure test barrel. These test barrels have minimum dimension chambers and bores to generate the highest possible test pressures. This way the test results will be safe in any firearm, but fire the same load in a used British military .303 rifle with a worn bore with cordite throat erosion and the pressure will be much lower.
Each rifle will be different, and we do not have pressure measuring equipment so we have to learn to read our primers and brass for pressure signs. You will do this by starting at the suggested starting load and working up reading your primers and brass and finding the limits of your brass. At AccurateShooter.com many of the long range shooter will increase the load until they see the brass starting to flow into the ejector and then they back off 1 or 2 grains of powder. They then fine tune the seating depth to come up with their accuracy load.
AccurateShooter.com has some of the best info on the net and you can spend week on the main page and in the forums getting some very good information.
http://www.accurateshooter.com/
Also "The Rifleman's Journal" is a wealth of information.
http://riflemansjournal.########.com/p/articles-index.html
The European CIP the equivalent of the American SAAMI considers the .308 Win and 7.62 NATO to be the one in the same cartridge rated at the same chamber pressure and the same applies for the .223/5.56. Our SAAMI sets dimensional "guidelines" for chambers and throats "BUT" these guidelines are not written in stone.
A military chamber is approximately .002 larger in diameter with longer headspace settings and the diameter of the chamber can effect the pressure slightly because it affects case capacity. The throat has the greatest effect on chamber pressure along with seating depth. But I can safely jam my .223 bullets into the rifling as long as I work up the load and stop at the first signs of excess pressure.
I was very surprised to find out my Savage .223 with a 1 in 9 twist had a longer throat than my AR15 rifles. What I found out was .223 rifles with a 1 in 14 or 1 in 12 twist will have shorter throats and shooting lighter bullets so there are many variables. Weatherby rifles rifles are famous for their high velocities and they do this with longer throats, BUT you won't find them winning any benchrest competitions with these long bullet jumps.
Below are .308/7.62 chambers, look at the base diameter, freebore diameter, freebore length and freebore angle. The freebore or throat dimensions have the greatest effect on chamber pressure and they also vary with your seating depth.
Below is is very telling about factory loads and chamber pressure, the green bar on the far left is a factory loaded .223 cartridge fired in a .223 rifle. The .223 and 5.56 are both rated at 52,000 cup or 55,000 psi but the factory .223 was only loaded to just below 50,000 psi. "BUT" the military loaded 5.56 NATO round the blue bar on the far right was loaded to approximately 55,000 psi. The two middle blue and green bars show the pressure differences between a SAAMI throat and the longer military throat.
Bottom line, no two firearms are identical, I was shooting two .357 revolvers over the weekend with my son and by looking at the primers I could see the fired case fired in his Ruger were slightly flatter than my S&W. If you look in the Lyman reloading manual you will see loads fired in a universal receiver and pressure test barrel. These test barrels have minimum dimension chambers and bores to generate the highest possible test pressures. This way the test results will be safe in any firearm, but fire the same load in a used British military .303 rifle with a worn bore with cordite throat erosion and the pressure will be much lower.
Each rifle will be different, and we do not have pressure measuring equipment so we have to learn to read our primers and brass for pressure signs. You will do this by starting at the suggested starting load and working up reading your primers and brass and finding the limits of your brass. At AccurateShooter.com many of the long range shooter will increase the load until they see the brass starting to flow into the ejector and then they back off 1 or 2 grains of powder. They then fine tune the seating depth to come up with their accuracy load.
AccurateShooter.com has some of the best info on the net and you can spend week on the main page and in the forums getting some very good information.
http://www.accurateshooter.com/
Also "The Rifleman's Journal" is a wealth of information.
http://riflemansjournal.########.com/p/articles-index.html
ROA explained it well. Most rifles can take high pressure loads and stand up just fine for awhile. Doesn't mean that you should continue shooting a high pressure load just because the brass or gun doesn't rupture
Work up a load, use a chrono for reasons suggested , and go from there. 2700 fps vs 2800 fps doesn't matter much in terms of performance but it could matter in pressure.
Work up a load, use a chrono for reasons suggested , and go from there. 2700 fps vs 2800 fps doesn't matter much in terms of performance but it could matter in pressure.
