CUP = PSI cart?

[LONGTOM]

Does anyone know where I might find a chart that gives CUP to PSI conversion. Some of my manuals list CUP and some list PSI.

Thanks
LONGTOM

[Graybeard]

There is no such chart because there is no direct correlation between them.

[LONGTOM]

I kind of thought so as I have never seen one.
I also see I posted under the wrong place again!
I will try and do better. Thanks for correcting my mistake.
This is a great place!!!!!!

LONGTOM

[steve4102]

  There is a mathematical formula for converting PSI to CUP and vis-versa.     Many experts say that this correlation is full of holes and can not be trusted.  Anyhow here it is.

http://www.shootingsoftware.com/ftp/psicuparticle2.pdf

[Graybeard]

Since there is no correlation between the two methods any such chart is merely adding to the confusion. Each individual cartridge can have a PSI and CUP determined which equate to each other but it varies by cartridge with some being the same and in some cases each of them is higher than the other.

There is just no direct relationship and trying to show one is a foolish endeavor and is counter productive.

[stimpylu32]

Until the industry sets a standard of either one or the other there will be confusion , now it is like apples & oranges , yes they are both fruit but that's were it stops .

In a prefect world , all testing would be done with the same test equipment , recorded the same way and printed the same way , until that happens we are still guessing to a point . Thats why we have to use what we know of pressure signs to work up loads and double check all the data we use .

stimpy

[Graybeard]

Well again sadly if you take all you know of pressure signs and all the rest of the reloaders of the world combined know about pressure signs and put it all in one bucket you won't have enough knowledge to buy a cup of coffee.

Those old wives tales of what to look for are a load of malarky and have been stated to be such these days by just about every known magazine writer in the business. I think they are finally coming around to the reality that if they keep on BS'ing folks that those signs have meaning they just might be on the losing end of a lawsuit some day.

Every test I've seen run comparing al those "pressure signs or indicators" to real world pressure data show them to be meaningless. You might see signs of high pressure even with the minimum starting charges or you might not at blue pill proof load levels. Believing you can tell what is safe in that matter is a recipe for disaster and it's time folks begun realizing it.

[steve4102]

Those old wives tales of what to look for are a load of malarky and have been stated to be such these days by just about every known magazine writer in the business. I think they are finally coming around to the reality that if they keep on BS'ing folks that those signs have meaning they just might be on the losing end of a lawsuit some day.

.

   So what is the solution to this problem?  How do we as handloaders know what is a safe load and what is not?  We certainly can't rely on the loading manuals.  To many variables and inconsistant data.  Remember the old saying "What is safe in one rifle may not be safe in another".  So, how do we determine what is safe in OUR individual rifles?

[Graybeard]

There really isn't any way to be 100% certain.

However there is a way to be reasonably sure. First own several loading manuals. I consider the minimum to be the Lyman manual and the manuals from all powder and bullet makers whose products you will be using.

Cross check the data for your rifle and your components in the manuals you have and determine what the average max charge is based on the manuals. You'll need to note whether they used a pressure barrel or a rifle when developing their data.

Determine a likely real world velocity maximum you should be able to expect using the powder and bullet you have on hand based on what the reloading manuals collectively tell you. Take barrel lengths used by then and what you have into account.

Then load up some loads and start shooting them over your chrono when you reach the book average max or the velocity they said was max STOP. That's an either or situation. Don't exceed the average max of the manuals but also don't continue to it once you've reached their average max velocity either.

It's not fool proof but in my opinion is as close as we can come without pressure testing equipment of our own. The real bottom line is there is just no way to be certain of your pressures or the safety of your reloads without pressure testing equipment. Thankfully the rifle makers build in a generous margin of error safety factor that helps us so long as we are not trying to take advantage of that margin to turn a standard round into a magnum round. Don't try to make the cartridge/rifle combination you have into something it is not designed to be. If you need more velocity buy a rifle chambered to a larger capacity round.

[jhalcott]

  This is where a chrono REALLY pays for it's self. When you start low and work up, you get to a point that the velocity increase stops or drastically slows. For instance ,for every 1 grain increase in powder ,you get 50 more FPS. After 4 or 5 powder increases ,you suddenly get ONLY 10/15 FPS more, you are at the max charge level. I drop back a half grain and test for accuracy and velocity at that point.  Just because the BOOK says 55 grains of XXX powder was THEIR max, it is not neccessarily MINE. Also if they say 2900 fps was reached with THEIR equipment, it doesn,t mean I will get it with MINE!

[steve4102]

  This is where a chrono REALLY pays for it's self. When you start low and work up, you get to a point that the velocity increase stops or drastically slows. For instance ,for every 1 grain increase in powder ,you get 50 more FPS. After 4 or 5 powder increases ,you suddenly get ONLY 10/15 FPS more, you are at the max charge level.

  When this occurs it is possible that you have reached max pressure.  It is also possible that you have not or you are over. It is also possible that you will continue with a linear increase in velocity without ever reaching your velocity change. This method is no more accurate than the others Graybeard is refering to.

[Lone Star]

Here is what the OP is looking for.   I have a 1990 vintage Hercules Powder Reloader's Guide with a chart that DOES list the psi and CUP for a variety of cartridges.   I can't find the chart on the Internet but as can be seen below the CUP=psi for the .45-70, but the units vary by 13,000 for the .270 WCF. 

This method is no more accurate than the others Graybeard is refering to.

Right on.  This is yet another old gunwriter's fantasy, not supported by any testing or fact.  There are so many things wrong with that particular method that it makes my head swim. 

.

[EsoxLucius]

Since there is no correlation between the two methods any such chart is merely adding to the confusion.

This statement is proven wrong by the statistics provided in the Bramwell article.  Given the assumptions and limitations provided in the article there is indeed a correlation between the CUP and PSI data as provided by SAAMI.  Now, how someone should use or infer information from such a formula is another story.

[FW Conch]

   Guys ! LISTEN to what Greybeard is saying. It doesn't matter about Copper Units of Pressure or Pounds Per Square Inch . What matters to a reloader is when it says " Max Load" that means maximum grains of "powder"!  Why do you think everyone tells you to start @ "minimum" & work your way up in .2 grain steps ?  There are variables, such as temperature, humidity, distance from lands, that can cause pressures to "spike" & these limits provide safe averages . If what you want is Feet Per Second get a 300 RUM & rattle your teeth. Then you'll find out why they're not selling, & "Big Green is dropping back to Level 2 & Level 1 ammo. But if you think you've got a "super action" that can handle any level of stupidity, load up, IT's  YOUR  FACE !

[Graybeard]

Since there is no correlation between the two methods any such chart is merely adding to the confusion.

This statement is proven wrong by the statistics provided in the Bramwell article.  Given the assumptions and limitations provided in the article there is indeed a correlation between the CUP and PSI data as provided by SAAMI.  Now, how someone should use or infer information from such a formula is another story.

I don't have a clue where you are coming from on that comment but it's grossly wrong. Just look at the bottom few chamberings on the above chart to prove it.

For the 45-70 they are both listed as the same.

For the .35 Remington CUP is higher than PSI.

For the .338 Win. Mag. PSI is higher than CUP.

Now if there is any direct correlation how the hell can that be? The numbers are all over the place there just is no correlation between the two methods of testing.

[steve4102]

   . What matters to a reloader is when it says " Max Load" that means maximum grains of "powder"!  Why do you think everyone tells you to start @ "minimum" & work your way up in .2 grain steps ?  There are variables, such as temperature, humidity, distance from lands, that can cause pressures to "spike" & these limits provide safe averages .

  OK, Max load means maximum grains of powder, understood.  So which manual or load data do you go by when it comes to determining max powder charge?  The load data out there is very inconsistant when it comes to max charge.  In many cases one set of data will have it's max charge less than start data in another.   
 
   So, "everyone tells you to start @ "minimum" & work up in .2 grain steps".  WHY?  What is the point?  What am I working up to?  If there are no real signs of over pressure and as a handloader I cannot determine what is over pressure, Why not just start at max and be done?  After all, as a handloader there is nothing that my brass can show me that would indicate high pressure.  Working up in small incriments is therefore a total waist of time where pressure is concerned. 

[Graybeard]

There is truth in what you say but really we have answered the question you ask already.

You need lots of reloading manuals. Some list the same bullet you will be using and most the same powder or you'd not be using the data to begin with. But do you use the same brand of case and primer or do they even list those? That's why the wide differences in data. Just because they use the same powder (from different lots no doubt) as you and the same weight bullet that might be the ONLY commonalities in your load and those in some manuals.

You need to find as many commonalities as possible. Receipes are to be used precisely meaning same brand case, same primer, same powder, same bullet seated to same dept. Even then you'll be using a different chamber to fire it in so your results will vary even if you used all the components from the same lots as they did which you never will.

Keep as many things the same as you can. Average the numbers in several manuals. Toss out any that are way out of line with the rest. Buy and use a chrono. When you reach the same velocity they did or reach that average max load STOP go no further. That's really about as safe as it gets with reloading if you don't have pressure measuring equipment.

Will that mean your pressures will always be within SAAMI specs? Nope sorry there are no gurantees.

Why go in increments? To find what load is most accurate in your gun. IF you are using the chrono you can also see a point where the powder charge no longer seems to give a linear velocity increase. What does that really mean to you? Dunno for sure but I have found that going higher seldom if ever improves accuracy from that point. It might mean you're reached optimum effectiveness of that powder in that use or it might not. But for sure going up in increments tells you when the load is most accurate and that is after all what you should be looking for isn't it?

[EsoxLucius]

I don't have a clue where you are coming from on that comment but it's grossly wrong. Just look at the bottom few chamberings on the above chart to prove it.

For the 45-70 they are both listed as the same.

For the .35 Remington CUP is higher than PSI.

For the .338 Win. Mag. PSI is higher than CUP.

Now if there is any direct correlation how the hell can that be? The numbers are all over the place there just is no correlation between the two methods of testing.

With all due respect, there appears to be a lack of understanding of what a correlation is.  All I'm stating is that Bramwell demonstrated that there is indeed a correlation between the published SAAMI CUP pressure standard and the published SAAMI PSI pressure standard.  Sure there will be individual instances where there is not a good fit, but that does not mean that there is no correlation within the entire set.  He has proven that there is a correlation and provided the math that demonstrates it.  He also states the assumptions made, limitations of the data, and limitations and recommendations for application.  Its called science.  Again, how one uses that information is another matter. 

I agree that even having information of a correlation between CUP and PSI values is of limited value as one should follow published load information and accepted reloading practices.  To do otherwise one is no longer a reloader but becomes an experimenter.

[LONGTOM]

Boys this all started over a want to re-chamber a factory barrel to something else that is not offered. I have read so much in the last couple of days, heck I don't even remember which calibers I was considering. All I know is the factory cartrige in all my manuals is listed as CUP and all my manuals list the cartrige I wanted to turn it into as PSI. Therefor how am I to know if the action will even stand the new round to begin with?


LONGTOM

[stimpylu32]

LONGTOM

What are you looking at as far as base round and what do you want to re-chamber to ? also what type action are you planning to use ?

stimpy

[quickdtoo]

I'd look at pressures for rounds the rifle is factory chambered in to get you in the ball park, then consider bolt/breech thrust/case head size comparison. 

Tim

http://data.hodgdon.com/main_menu.asp

[LONGTOM]

Hi stimpylu32:
I have kicked so many ideas around the last few days I really don't remember. I think I was considering trying to do a 270AI and was considering a 6.8 starter but I now know they don't offer the 6.8. It would be on a SB2 frame. Idealy I would like to come close to a 270WSM somehow, not to sure where I would get a barrel long enough. If they would just make the darn thing it sure would make life a lot easier. I see they have the MAG frames listed in the new catalog but when will we ever see them!

LONGTOM

[LONGTOM]

Dreams, just Dreams! Or maybe I should say add to the wish list.

LONGTOM

[stimpylu32]

LONGTOM

In the H&R platform about the best you can hope for is the 280 Remington in a 26" barrel , the 270wsm is just way too much for this design .

stimpy

[Sweetwater]

Sounds like you need the services of a gunbuilder with a ballistics engineer on staff. As pointed out, the 270WSM or similar may be inappropriate for the H&R platform, but there are other platforms - you get to make some choices and then give it to the pros to sift through and come up with the 'what ifs' for you to consider. They will also give you the necessary guidelines for your ammunition loading.

These requirements I didn't see when I first read the OP.  But, really sounds like what you were looking for - some of this stuff is just a bit beyond what hobby handloaders get involved with.

Graybeard gave you some good scoop there and the nuts and bolts answer to the OP. Having a relationship and having a direct relationship to two very different things and from what I've read here, I don't believe many of us are into the statistical explanation of it all. There is no direct relationship as GB pointed out. It's easy to get into unsafe conditions when you stray beyond the written guidelines by very much. Chronographs can help and can also give you erroneous readings. Each weapon is an individual, which is a big reason the manuals don's all agree on specific charges or specific velocities - that's why they are guides. "We" have to be smart enough to keep ourselves in the safe area. Any time I've gone 'overboard' in my quest for answers, my weapon of inquery has "always" told me it didn't like what I was doing. I've learned to listen to them as well as our experienced collegues.

Some of this you don't find in a book - you see it downrange, or at your shoulder, in your wrists, or in your ears. Recognize it.

My question on pressure has always been, since SAAMI did not manufacture my weapon, and XXX Inc makes it in a 260Rem, a fairly high pressure round, why am I limited to say 3/4's of that pressure because mine happens to be chambered for 6.5x55 or say a 35Remington? What am I missing here? Seems like I don't need to buy another rifle, but to simply upgrade the performance of the cartridge I have to the levels of others in the same action.  Response?

Regards,
Sweetwater

[EsoxLucius]

Having a relationship and having a direct relationship to two very different things and from what I've read here, I don't believe many of us are into the statistical explanation of it all. There is no direct relationship as GB pointed out.

direct correlation, noun - a correlation in which large values of one variable are associated with large values of the other and small with small; the correlation coefficient is between 0 and +1; the closer to 1 the greater the correlation

Bramwell showed that there is a direct correlation between published SAAMI CUP and published SAAMI PSI values subject to the limitations stated in the article.  Did any of you actually read the article?  You might learn something.  http://www.shootingsoftware.com/ftp/psicuparticle2.pdf

If this gentleman wants to know what his rifle will withstand in PSI based on a chambering of a cartridge he only finds CUP pressures for he can be pretty sure that (CUP*1.51586)-17902≈PSI will get him close enough to make a judgment.  Using the chart that shows the CUP and PSI values for 30 or so cartridges, he can also compare the CUP value of his cartridge with the PSI values of cartridges with the same or similar CUP rating and evaluate it based on that.  Inference supported by data is a wonderful thing.

Cartridge ANSI CUP ANSI PSI
222 rem 46000 50000
22-250 rem 53000 65000
243 win 52000 60000
25-06 rem 53000 63000
257 roberts 45000 54000
264 win mag 54000 64000
270 win 52000 65000
280 rem 50000 60000
284 win 54000 56000
30 carbine 40000 40000
300 savage 46000 47000
300 win mag 54000 64000
30-06 springfield 50000 60000
303 british 45000 49000
30-30 win 38000 42000
308 win 52000 60000
32 win special 38000 42000
338 win mag 54000 64000
35 rem 35000 33500
375 h&h mag 53000 62000
444 marlin 44000 42000
45-70 government 28000 28000
6.5 rem mag 53000 65000
6mm rem 52000 65000
7mm express Rem 40000 45000
7mm rem mag 46000 51000
7mm SE vH 52000 61000
7x50 R 52000 61000
8mm mauser 37000 35000
8x50R 54000 65000

[quickdtoo]

I see they have the MAG frames listed in the new catalog but when will we ever see them!

LONGTOM

The Handi-mags were canceled in January even tho they were published in the 2008 catalog.

Tim

[steve4102]

.



.  . Any time I've gone 'overboard' in my quest for answers, my weapon of inquery has "always" told me it didn't like what I was doing. I've learned to listen to them as well as our experienced collegues.

Some of this you don't find in a book - you see it downrange, or at your shoulder, in your wrists, or in your ears. Recognize it.



Regards,
Sweetwater

  Sounds all well and good, cept we have been told here that these signs you speek of are worthless.  I quote, "if you take all you know of pressure signs and all the rest of the reloaders of the world combined know about pressure signs and put it all in one bucket you won't have enough knowledge to buy a cup of coffee."  End Quote.

[Chris Potts]

<sup>I read Bramwell's  entire article.  There are a couple of things that I would like to point out about his analysis.

1. The correlation only applies to the numbers tested. He compared the published saami maximum psi and cup of 30 cartridges.  According to is findings there is a .927 correlation between the maximum saami standards for cup and psi for those 30 cartridges.  To claim that this correlation applies to all cartridges takes you outside the realm of science and statistics.  As soon as you use the data acquired by testing a sample and apply it to entire group you begin to make assumptions.  These assumptions may be good but they are not scientifice.  They have not been proven.  It is merely a hypothesis.

2.  He states that "a R2 of .8 means that 80% of one variable is "controlled" by the other."  This is simply untrue.  You can never say with any degree of confidence that one variable controlls another simply through statistical anaylsis.  Statistics analysis does not deal with the causation.  One of the first things that I was ever taught in statistics is that correlation does not prove causation.  You can only prove that there is a correlation between the tested variables.  Furthermore, this correlation does not necessarily mean that there is a relationship between the variables.  Even Bramwell Acknowledges that two groups of random numbers will most often correlate to one another (not necessarily to a high degree).  Also it is not necessarily uncommon to find a high correlation between variables that we can all but eliminate as being related to one another.  One of the classic examples is that there is a high (80%) correlation between the winner of the super bowl and how the stock market will perform that calender year. 
http://www.snopes.com/business/bank/superbowl.asp

Another thing that I find interesting is that in all of the cartridges that he looked at the psi was equal or higher than the cup.  As Graybeard pointed out there are cartridges where the cup is higher than the psi.  The simple fact that some cartridges have a higher cup than psi rating does not mean that cup and psi are not correlated.  These cartridges could just be an anomoly.  However, it does suggest that his numbers may be overstated because he did not include any of these cartridges.


I am going to stop there but I don't really think that he so called "scientific proof" is definitive.

Chris Potts</sup>

[LONGTOM]

Sweetwater is getting closer to what I was thinking.
For example: I talked to TC some time ago about building a 307 WIN on a contender action and they said no because it could be hand loaded to to high a pressure yet they made a 375 WIN which was either the same or a tad higher that the 307. That makes no sence to me. Could not the 375 be loaded to a higher presure also.
In both types of actions, the TC and the SB2 I was trying to see what different calibers could possibly be done and still stay within the realms of what each could safely take.

EsoxLucius The chart at least helps define a few to compare with. Thanks to all. It is all sound advice.

LONGTOM