Expansion Ratio

[chkunz]

Does anyone have a source for expansion ratios? I know a table listing expansion ratios would be for a specific bullet, seating depth etc. but nominal values might be helpful. I can calculate this myself but if someone else has published something on this it then I would prefer starting with that.

 

[dedogs]

TRex, I found a formula last year by just typing in Expansion Ratio in yahoo search. I believe it took me to an article posted on 24 HR Campfire. Don't have the link or I would post it for you. Hope this helps. dedogs

 

[GrocMax]

Generally described as P2/P1, where P2 is the high pressure, P1 is the low pressure, and both pressures are in absolute units.

The equivalent of Pressure Ratio, where compression occurs, just called Expansion Ratio because expansion occurs.

 

[chkunz]

Generally described as P2/P1, where P2 is the high pressure, P1 is the low pressure, and both pressures are in absolute units.

The equivalent of Pressure Ratio, where compression occurs, just called Expansion Ratio because expansion occurs.

I should have been more specific with my question. Expansion ratio as it applies to reloading is simply the ratio of the total volume of the gun to case capacity, it is the number of times that the gas expands by the time that the base of the bullet reaches the exit of the muzzle.

 

[chkunz]

TRex, I found a formula last year by just typing in Expansion Ratio in yahoo search. I believe it took me to an article posted on 24 HR Campfire. Don't have the link or I would post it for you. Hope this helps. dedogs

Thanks I will look it up and see what I can find. I was not looking for a formula though because I know how to calculate it. What I would like to find is a table with typical values for various cartridges and barrel lengths. For a given configuration it will vary slightly depending on the seating depth of the bullet. I could build my own table but I am lazy and first would like to see if someone else has done it.

 

[Nvreloader]

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

 

[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

That sound like what I am looking for.

 

[Webster]

Can you explain what you use the expansion ratio for? The ratio of case capacity to bore volume doesn't consider the huge volume of gas generated by the powder. The volume of gas generated by the powder varies with charge weight and burning rate?????? The powder probably generates a volume at least a 1000 times greater than the powder itself. I think that all that matters is the pressure VS time curve while the bullet is in the barrel.

 

[Bronsin]

Try this.......

http://kwk.us/powley.html

 

[chkunz]

Can you explain what you use the expansion ratio for? The ratio of case capacity to bore volume doesn't consider the huge volume of gas generated by the powder. The volume of gas generated by the powder varies with charge weight and burning rate?????? The powder probably generates a volume at least a 1000 times greater than the powder itself. I think that all that matters is the pressure VS time curve while the bullet is in the barrel.

Expansion ratio is not "the ratio of case capacity to bore volume".

 

[gunsandgunsmithing]

Maybe helpful..maybe not.
http://www.accurateshooter.com/technical-articles/overbore-cartridges-defined-by-formula/

 

[chkunz]

Maybe helpful..maybe not.
http://www.accurateshooter.com/technical-articles/overbore-cartridges-defined-by-formula/

Thanks for taking the time to send this but it is really not what I am looking for. The case capacity listed in the table appears to be the empty case capacity to the top of the neck and is useful information but the case capacity used in the expansion ratio calculation is the volume available for powder after the bullet is seated and is a little different for each bullet configuration. I thought someone might have constructed a table of several different cartridges and barrel lengths to give an overview of this parameter. I may have to build the table myself, it would just take a few hours of work and not that difficult to do but if someone else has done the work then I would prefer to take advantage of that work. Thanks again and take care.

 

[chkunz]

Try this.......

http://kwk.us/powley.html

Thanks. I tried this and it works well and easy to deal with. This does the tedious part of dealing with bullet lengths and seating depths. I did not check it against one of my calculations but I assume it is accurate. It is based on the work done by Homer Powley in the 1960s of which I am familiar.

 

[chkunz]

Can you explain what you use the expansion ratio for? The ratio of case capacity to bore volume doesn't consider the huge volume of gas generated by the powder. The volume of gas generated by the powder varies with charge weight and burning rate?????? The powder probably generates a volume at least a 1000 times greater than the powder itself. I think that all that matters is the pressure VS time curve while the bullet is in the barrel.

There is a good article in "Handloading" by William C. Davis, Jr. an NRA publication from January 1981. The title of the article is "Some Simplified Interior Ballistics for Handloaders". There are other references that explain this parameter (expansion ratio) and how it is used in calculating internal ballistics. Folks today do not often use the hand calculations presented in this article, they use the computer programs available today but a study of the old methods help to understand the basic physics involved if there is still anyone who is interested. Anyway the expansion ratio of most target rifles is on the order of 10 not 1000.

 

[JarheadAZ]

The Accurate Shooting overbore chart is what prompted me to eliminate the .308 from my shooting activity and concentrate of the .260 and .30-'06. It confirmed to me that the .308 was simply not adequate for reliable results in my limited prowess at 1000yd. It was like boxing with a hand tied behind compared to the .260. It also helped establish the peak level of punishment I am willing to inflict on my bore's throat, achieving the desired results without needing to run the hotter loads.

Beyond helping select a chambering, I have little further use for such charts.

Greg Langelius

 

[gunsandgunsmithing]

The Accurate Shooting overbore chart is what prompted me to eliminate the .308 from my shooting activity and concentrate of the .260 and .30-'06. It confirmed to me that the .308 was simply not adequate for reliable results in my limited prowess at 1000yd. It was like boxing with a hand tied behind compared to the .260. It also helped establish the peak level of punishment I am willing to inflict on my bore's throat, achieving the desired results without needing to run the hotter loads.

Beyond helping select a chambering, I have little further use for such charts.

Greg Langelius

What stands out to me about the chart is the top five. With the exception of the 458 win mag..which for obvious reasons doesn't fit the same conclusion, the others are some of the absolutely most accurate cartridges ever designed. I don't think that's a coincidence. I'd venture to say, that with good bullets and a heavy enough gun to control the recoil, even the 458 would be a very accurate caliber. Of course, if frogs had wings...yada, yada. A good case for all of the top 10 in that chart can be made.

 

[JarheadAZ]

I concur; and I also suggest that a borderline overbore cartridge can be made to behave a bit better by trying to find a node as closely aligned with the published minimum charge as can be practical.

While I don't immediately see a cartridge in between the .223 and the .22-250, I venture that a 22-250 with a milder load could serve needs ranging from a hot loaded .222 to the full blown .22-250. I have shot the .22-250 downloaded to as far as 9gr of Unique with the 52gr SMK, as well as 36.0gr of Varget with the same bullet.

Far from ideal, it still serves to illustrate that creative handloading can serve more needs than most imagine, including eliminating the need to play around with wildcats.

I would also venture that playing around with charges that trample the limits of published data is no task for a beginning handloader. There is true danger lurking beyond those published load limits. One hint/suggestion is that when going below published minimums, switching to faster, rather than a slower, powder burn rate would be highly advisable.

I have learned, with some personal discomfort, that nothing good lurks beyond published maximums. It may seem to work, but twisting the dragon's tail will always have a serious downside eventually. Two items hot rodders usually overlook are Metal Fatigue and MTBF. If you have to look them up, then you really should look them up.

I could tell beginners not to do this or that, but they're going to grow up and go there anyway someday. I did, eventually. I'd rather see them approaching that dark cave mouth with a flashlight in their hands than not.

...And, a milder load treats the rifle's bore with more respect.

Greg

 

[gunsandgunsmithing]

I concur; and I also suggest that a borderline overbore cartridge can be made to behave a bit better by trying to find a node as closely aligned with the published minimum charge as can be practical.

While I don't immediately see a cartridge in between the .223 and the .22-250, I venture that a 22-250 with a milder load could serve needs ranging from a hot loaded .222 to the full blown .22-250. I have shot the .22-250 downloaded to as far as 9gr of Unique with the 52gr SMK, as well as 36.0gr of Varget with the same bullet.

Far from ideal, it still serves to illustrate that creative handloading can serve more needs than most imagine, including eliminating the need to play around with wildcats.

I would also venture that playing around with charges that trample the limits of published data is no task for a beginning handloader. There is true danger lurking beyond those published load limits. One hint/suggestion is that when going below published minimums, switching to faster, rather than a slower, powder burn rate would be highly advisable.

I have learned, with some personal discomfort, that nothing good lurks beyond published maximums. It may seem to work, but twisting the dragon's tail will always have a serious downside eventually. Two items hot rodders usually overlook are Metal Fatigue and MTBF. If you have to look them up, then you really should look them up.

I could tell beginners not to do this or that, but they're going to grow up and go there anyway someday. I did, eventually. I'd rather see them approaching that dark cave mouth with a flashlight in their hands than not.

...And, a milder load treats the rifle's bore with more respect.

Greg

Ok..so what is MTBF, in reloading context?

 

[dedogs]

Mean time Between Failures

 

[gunsandgunsmithing]

Mean time Between Failures

Thanks! I thought that may be what he was referring to, but due to pressure?? I'm going on 40 years of reloading...between failures.