Are burn rate and pressure curve synonymous?
- Thread starter Tommie
- Start date
One of the most interesting questions to come along. I think the powder makers or reloading manuel makers would be best suited to answer that accurately.
Yes.
Some other variables in ammo that change pressure curves; some more than others:
* powder temperature.
* primer flame.
* bullet release force.
* position of powder in case when primer fires (ever heard of the "SAAMI twist" specification?)
* bullet diameter, jacket hardness and jump to the rifling.
The barrel inside dimensions across several can also cause different pressure curve shapes for a given cartridge. And firing pin spring strength variables and how deep the pin dents are changes the primer flame output.
Some other variables in ammo that change pressure curves; some more than others:
* powder temperature.
* primer flame.
* bullet release force.
* position of powder in case when primer fires (ever heard of the "SAAMI twist" specification?)
* bullet diameter, jacket hardness and jump to the rifling.
The barrel inside dimensions across several can also cause different pressure curve shapes for a given cartridge. And firing pin spring strength variables and how deep the pin dents are changes the primer flame output.
True. I should have included “All other variables being equal” in my question.
Yes, they still can have different pressure curves. While the pressure curve shapes will have less differences, they'll be enough to produce different velocities and peak pressures.
There's enough difference across all lots of a given powder's same charge weight to produce a few dozen fps in velocity and a few thousand peak psi numbers in a given barrel.
I’m not really asking about lot to lot differences or other variables. Somehow I’m failing to ask the question correctly. Let me try this:
If two different powders have the same exact burn rate will these two powders have the exact same pressure curve. ALL other things being equal. In other words: will a measured burn rate have a predictable pressure curve?
If two different powders have the same exact burn rate will these two powders have the exact same pressure curve. ALL other things being equal. In other words: will a measured burn rate have a predictable pressure curve?
I don't know if this is an answer to your question, but as an old cannon cocker, I have always found propellants interesting. Read the section on propellants in section 1-6
http://halosix.net/resources/ops/FM/reference/us_army_cc_fa9011_ballistics.pdf
http://halosix.net/resources/ops/FM/reference/us_army_cc_fa9011_ballistics.pdf
dmoran
Donovan Moran
Probably not.
I'm not aware of powders being given a specific burn rate number that's repeatable across all lots of a given make and type. Therefore, how do you pick two that are exactly the same for a given cartridge, primer and bullet?
Here is an attempt to assign relative burn rate values.
http://www.chuckhawks.com/powder_relative_burn_rate.htm
Problem with it is, the exterior ballistics one lot of components produces will vary across different rifles. A 3% to 4% spread in a given powder's charge weights to meet velocity and pressure specs for military and commercial ammo is normal. And the same rifle and components will produce different velocities across several people.
Last edited:
dellet
Gold $$ Contributor
If two different powders, perform the same under the same test conditions in a lab. In theory they will perform the same under the same conditions in the field.
If you change the conditions, the answer will likely change. They may perform exactly the same with a 150 grain bullet, but not with a 175.
Burn rate charts group powders of the same relative quickness, within a given window. So by definition getting exact results, same exact pressure curve. From relative comparisons is not likely to happen.
If you change the conditions, the answer will likely change. They may perform exactly the same with a 150 grain bullet, but not with a 175.
Burn rate charts group powders of the same relative quickness, within a given window. So by definition getting exact results, same exact pressure curve. From relative comparisons is not likely to happen.
"Are burn rate and pressure curves synonymous"......
I'd vote yes,BUT....in a very narrow testing window.Which may,not be predictable.It'll sort of "just happen" when the conditions are exactly in sync.Generally not something that is transferred or,IMO should be a focus for improved loading(handloading for optimal performance).
I'd vote yes,BUT....in a very narrow testing window.Which may,not be predictable.It'll sort of "just happen" when the conditions are exactly in sync.Generally not something that is transferred or,IMO should be a focus for improved loading(handloading for optimal performance).
I have read often that they do......ie: "beware when loading at the top with 4064 that it peaks quickly ". To me this means that it burns quicker .....pressure peaks quicker, when loading max. charges.
The implied question behind this is...
Does the speed at which a powder burns track perfectly with the amount of gas that the burned powder produced?
I would imagine its possible for powder A and powder B to burn at identical rates (ie complete combustion in xx milliseconds) but for one powder to produce more total volume of gas than the other. If that's true, then the pressure curves would not be identical.
Does the speed at which a powder burns track perfectly with the amount of gas that the burned powder produced?
I would imagine its possible for powder A and powder B to burn at identical rates (ie complete combustion in xx milliseconds) but for one powder to produce more total volume of gas than the other. If that's true, then the pressure curves would not be identical.
This is exactly correct.
Single base powders burn and produce gas differently to double base powders.
Single base powders burn hotter and release gas at an ever increasing rate as temp & pressure rise. There are progressive, digressive and neutral burn propellants. Examples in both single and double base are: progressive H4350, digressive RE25 & neutral W760. These factors govern burn curve as much as burn rate does.
Double base powders burn cooler and release more energy and gas differently to single base powders. The nitroglycerine content changes the release of gas to a more progressive event.
Due to these differences, the max pressure, and the curve, are quite different.
So, 2 powders that are the same in burn rate, which is NOT CONSTANT by the way, but different in composition will NOT have the same curve under peak pressure. Even if 2 powders of the same composition had identical burn rates, it is unlikely the curve would be the same.
It is also not true that a powder that produces x velocity will have the SAME max pressure as another powder that produces the SAME velocity. This simply isn’t even close to the facts.
Cheers.
This is exactly correct.
Single base powders burn and produce gas differently to double base powders.
Single base powders burn hotter and release gas at an ever increasing rate as temp & pressure rise. There are progressive, digressive and neutral burn propellants. Examples in both single and double base are: progressive H4350, digressive RE25 & neutral W760. These factors govern burn curve as much as burn rate does.
Double base powders burn cooler and release more energy and gas differently to single base powders. The nitroglycerine content changes the release of gas to a more progressive event.
Due to these differences, the max pressure, and the curve, are quite different.
So, 2 powders that are the same in burn rate, which is NOT CONSTANT by the way, but different in composition will NOT have the same curve under peak pressure. Even if 2 powders of the same composition had identical burn rates, it is unlikely the curve would be the same.
It is also not true that a powder that produces x velocity will have the SAME max pressure as another powder that produces the SAME velocity. This simply isn’t even close to the facts.
Cheers.
THANK YOU!
No. Ball and stick powders are very different.
http://www.firearmsid.com/Feature Articles/McCord_gunpowder/
I would also like to add that burn rate charts are NOT accurate, as no set STANDARD has ever been devised as to HOW they are listed and how they determine WHAT powder the others are RATED against.
For instance, IMR 4895 is rated at 100RQ by IMR. RQ is “ Relative Quickness”, BUT, H4895 is NOT given the same 100RQ value by Hodgdon or ADI who manufacture it.
Each powder manufacturer has their OWN powder they use as THEIR standard to determine RQ numbers, so it can only be taken as a rough GUIDE as to what MAY be similar.
Another very IMPORTANT factor is that burn rates are NOT, and have NEVER been, constant.
Burn rate changes with case size, shape, bore size and bullet weight.
The best way to determine an IDEA of what powders are suitable for any particular cartridge is to look at expansion ratio, it’s easy to gauge what burn rate works best when looking at this.
Hope this helps.
Cheers.
For instance, IMR 4895 is rated at 100RQ by IMR. RQ is “ Relative Quickness”, BUT, H4895 is NOT given the same 100RQ value by Hodgdon or ADI who manufacture it.
Each powder manufacturer has their OWN powder they use as THEIR standard to determine RQ numbers, so it can only be taken as a rough GUIDE as to what MAY be similar.
Another very IMPORTANT factor is that burn rates are NOT, and have NEVER been, constant.
Burn rate changes with case size, shape, bore size and bullet weight.
The best way to determine an IDEA of what powders are suitable for any particular cartridge is to look at expansion ratio, it’s easy to gauge what burn rate works best when looking at this.
Hope this helps.
Cheers.
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