Expansion Ratio

[dedogs]

Then I suspect you don't often if ever load over book max, which is what Jarhead was referring to. It's kind of like Catholic Birth Control.

 

[gunsandgunsmithing]

Then I suspect you don't often if ever load over book max, which is what Jarhead was referring to.

I wouldn't say that. Are you guys talking AR's or some other kind of tactical stuff? If so, then I understand, now.

 

[wolley]

What in the hell are you guys pondering? And why does it matter? How can it help?
In my mind expansion ratio should be nothing more than the volume of gas created by a known charge. That could then be used to calculate ballistic efficiency based on the volume of the barrel(I.E. length x bore+ case volume) Plus a whole bunch of other deep physics involving friction, bullet weight, compressibility of the air ahead of the bullet,.......
Then again you could just use Quick load.
WTF, Over? Really?

 

[Laurie]

I'm with Wes on this. I can't see where this thread is leading, or what relevance expansion ratio has except as a rough guide to cartridge design efficiency and performance.

 

[MS50]

I wandered into this thread out of curiosity. I've read, and heard from fellow shooters that I should develop a load that is as fast as my equipment will allow. I ran into a high pressure situation with my 223 that put an end to shooting that rifle for the day. I backed off about 100fps, found a node, and have a more accurate and easier to shoot load. As long as my load is supersonic at the distance I'm shooting, why would I want to test limits? My philosophy is develop a load that is as slow as I can find that will meet my needs. The gee whiz factor is high in the reloading game. The average reloader (me) shouldn't get caught up in theoreticals.

 

[chkunz]

I wandered into this thread out of curiosity. I've read, and heard from fellow shooters that I should develop a load that is as fast as my equipment will allow. I ran into a high pressure situation with my 223 that put an end to shooting that rifle for the day. I backed off about 100fps, found a node, and have a more accurate and easier to shoot load. As long as my load is supersonic at the distance I'm shooting, why would I want to test limits? My philosophy is develop a load that is as slow as I can find that will meet my needs. The gee whiz factor is high in the reloading game. The average reloader (me) shouldn't get caught up in theoreticals.

If you look at my original post you will see that I asked a simple question, does anyone know of a table that lists nominal expansion ratios for various cartridges, for specific bullets and barrel lengths. Apparently that does not exist so the thread has taken on other topics and even some implied criticism for me asking the question. I did not find what I am looking for but hopefully there has been something of benefit to others.

 

[dedogs]

The seeking out of expansion ratios is just as laurie described and is quite useful in the development of wildcat cartridges. Also some of us like to crunch numbers... and can still make change without the aid of a computer program or calculator.

 

[gunsandgunsmithing]

I've learned a thing or two in this thread, but I had the option of reading or posting in it from the start. I think we all do.
T-Rex, I'd be interested in hearing more from you once you've had time to build your chart. Thanks!--Mike

 

[chkunz]

I've learned a thing or two in this thread, but I had the option of reading or posting in it from the start. I think we all do.
T-Rex, I'd be interested in hearing more from you once you've had time to build your chart. Thanks!--Mike

Thanks for the encouragement. I have gotten lazy and it is easier to simply use the work of others than do the work myself. If I do not find what I am looking for then I may do this during the winter when time on the range is limited. Most folks simply use the nice programs that are now available to get the answers that they want. I graduated from engineering school with a slide rule and log tables so I tend to learn more if I work closer with the equations and the data. I also find that sometimes when I do calculations for one thing it gives me insight into something else. Also, it gives me better insight into the output of the computer programs. Take care, Clyde.

 

[MS50]

Sorry TRex, no criticism intended. I took a wrong turn at the overbore chart and thought we were talking about max pressures, etc. Good luck with your project.

 

[chkunz]

Sorry TRex, no criticism intended. I took a wrong turn at the overbore chart and thought we were talking about max pressures, etc. Good luck with your project.

No problem, it is a very narrow subject, just something I am interested in and thought it might give me some insight into some questions that I have. Take care, Clyde.

 

[Brians356]

FWIW, P. O. Ackley had a lengthy section in his Volume I titled as I recall "Bore Capacity" which you may find useful. It is not a scholarly treatise but I believe it will reward anyone seeking viewpoints on expansion ratios, relative efficiency, etc.

 

[Laurie]

Bear in mind though that when P O was writing his books, 4350 was as slow burning a powder as you'd generally find available. In fact, I'm sure he says somewhere in his two volumes that it's slower burning than he can contemplate seeing much use for.

Today, in a world of Retumbo, H1000 et al in everyday handloading some people regard the 4350s as medium rate almost fast powders. Our perceptions as to what is the correct v 'over' bore capacity have changed drastically in a half century, hence the market for very slow burners.

Dr Geoff Kolbe in his book on internal ballistics published many moons back has a chart with a graph line running through a load of cartridges / case capacities v calibres with the 7mm Rem Magnum right on it and regarded on the theoretical rationale used as being right on the borderline. Anything on the wrong side of the line above the 7RM fell into the over capacity on that basis. Whether many would still regard the 7RM and its 82gn water capacity case as marginal over [7mm] bore capacity now is a moot point as substantially larger cases can be usefully employed with many of the powders introduced since Geoff did this work.

However, the simple rule that the smaller the charge, the higher the thermal efficiency and vice versa never changes. There isn't anything much around that matches the standard vel .22LR with 1.6gn of powder giving a 40gn bullet an MV of 1,050 fps and ~100 ft/lb ME or 60 ft/lb + per 1.0gn powder. No matter how many new cartridges and powders have appeared, no matter how many claims are made that some super new cartridge case shape with a different length to diameter ratio and precisely researched shoulder angle will 'revolutionise' cartridge efficiency, the rule of thumb that says that you divide any % change in case capacity / charge weight in a given calibre by 4 to get the resulting % velocity change provided all other factors (case fill-ratio, pressures, bullet, and barrel length) are the same still holds up pretty well.

Since the .22LR generally makes a very poor 1,000 yard F-Class or elk cartridge, we have to have larger and less efficient cartridges and a large percentage of threads on this forum are in essence asking for opinions on the various factors and trade-offs between calibres and cartridges for a given task (or all too often rather shortsightedly don't mention the task and shooting distances but just ask what's the 'best cartridge'!).

The simple answer is usually twofold (for competitive shooting anyway):

the smallest case that does the job fully.
what the winners use.

which may not always be the same thing

 

[Brians356]

Bear in mind though that when P O was writing his books, 4350 was as slow burning a powder as you'd generally find available. In fact, I'm sure he says somewhere in his two volumes that it's slower burning than he can contemplate seeing much use for.

Your general point taken, although I'm fairly certain 4831 appears frequently in Ackley's data. Nevertheless, general principles of the subject he discusses are pertinent today.

 

[chkunz]

Bear in mind though that when P O was writing his books, 4350 was as slow burning a powder as you'd generally find available. In fact, I'm sure he says somewhere in his two volumes that it's slower burning than he can contemplate seeing much use for.

Today, in a world of Retumbo, H1000 et al in everyday handloading some people regard the 4350s as medium rate almost fast powders. Our perceptions as to what is the correct v 'over' bore capacity have changed drastically in a half century, hence the market for very slow burners.

Dr Geoff Kolbe in his book on internal ballistics published many moons back has a chart with a graph line running through a load of cartridges / case capacities v calibres with the 7mm Rem Magnum right on it and regarded on the theoretical rationale used as being right on the borderline. Anything on the wrong side of the line above the 7RM fell into the over capacity on that basis. Whether many would still regard the 7RM and its 82gn water capacity case as marginal over [7mm] bore capacity now is a moot point as substantially larger cases can be usefully employed with many of the powders introduced since Geoff did this work.

However, the simple rule that the smaller the charge, the higher the thermal efficiency and vice versa never changes. There isn't anything much around that matches the standard vel .22LR with 1.6gn of powder giving a 40gn bullet an MV of 1,050 fps and ~100 ft/lb ME or 60 ft/lb + per 1.0gn powder. No matter how many new cartridges and powders have appeared, no matter how many claims are made that some super new cartridge case shape with a different length to diameter ratio and precisely researched shoulder angle will 'revolutionise' cartridge efficiency, the rule of thumb that says that you divide any % change in case capacity / charge weight in a given calibre by 4 to get the resulting % velocity change provided all other factors (case fill-ratio, pressures, bullet, and barrel length) are the same still holds up pretty well.

Since the .22LR generally makes a very poor 1,000 yard F-Class or elk cartridge, we have to have larger and less efficient cartridges and a large percentage of threads on this forum are in essence asking for opinions on the various factors and trade-offs between calibres and cartridges for a given task (or all too often rather shortsightedly don't mention the task and shooting distances but just ask what's the 'best cartridge'!).

The simple answer is usually twofold (for competitive shooting anyway):

the smallest case that does the job fully.
what the winners use.

which may not always be the same thing

You provide a lot of good information and thought on "over bore" and new powders etc. but this goes way beyond my question. I am just looking for an easy way to get expansion ratio for a variety of chamber/bullet/barrel length configurations. This is a simple physical parameter of each gun configuration that has a direct bearing on internal ballistics, the utilization of this internal ballistic parameter is another subject altogether. But I am sure the information you have provided will be of interest to others, thanks.

 

[chkunz]

FWIW, P. O. Ackley had a lengthy section in his Volume I titled as I recall "Bore Capacity" which you may find useful. It is not a scholarly treatise but I believe it will reward anyone seeking viewpoints on expansion ratios, relative efficiency, etc.

I do have the Ackley book, Volume I/II and have read the section you refer to, "Bore Capacity" page 165. It would be of some value as background information for someone who wanted to understand expansion ratio and how to use the parameter for internal ballistics. Thanks for noting the reference, some folks who are interested in the subject might find it useful. Someone noted in another reply that the information is somewhat dated due to the powders that were available at the time. However expansion ratio is a physical characteristic of each bun configuration and is not dependent on other parameters. Thanks again for noting the reference.

 

[Brians356]

Did anyone previously reference this forum thread? Might be a few kernels of insight in there ...

https://www.shootersforum.com/ballistics-internal-external/59503-bore-capacity-expansion-ratio-math-help.html

Wouldn't QuickLoad provide this particular datum as one of its products?

 

[chkunz]

T Rex

What calibers are you looking for?

RCBS load has the bbl expansion for all the calibers they list.
They list for the 10",18 26" bbl's.

Tia,
Don

Thanks for the reference. I do not have RCBS Load but I may buy it since it has expansion ratio listed for their data, before I go too far down this road. This might be a good starting point and I could expand with my own calculations if I decide to put the effort into it.

 

[chkunz]

Did anyone previously reference this forum thread? Might be a few kernels of insight in there ...

https://www.shootersforum.com/ballistics-internal-external/59503-bore-capacity-expansion-ratio-math-help.html

Wouldn't QuickLoad provide this particular datum as one of its products?

I too a look at the link and it was some guys having some fun with how to calculate it and a first order effort to understand what it means. I do not have QuickLoad so I do not know if it provides the expansion ratio as one of the calculated parameters. Thanks.

 

[corsair4360]

I have an updated set of tabular data from my research. The newer Nosler cartridges data are my least comfortable data point(s). I have asked the moderator to get the process started for an update, we will see what happens. I now have 170+ cartridges in the list. I attempted to cut and paste the data, but it was at best hard to read.