powder burn rates?
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RecoilRob
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Wow....someone could spend a LOT of bandwith on this one!!
But..trying to simplify: There are a couple different ways you are limited with your powder selection...the first by chamber pressures. A small amount of very fast burning powder can make the maximum allowable pressure but won't deliver great performance because it's done burning so quickly that in a long rifle barrel it stops pushing before the bullet leaves the tube.
A greater amount of slower burning powder can make the same maximum pressure but does it more gradually and pushes longer so the velocity attained will be greater in a longer barrel. This continues until you start to run into the other constraining factor which is the capacity of the case. Using too slow a powder will fill the case to the brim without being able to attain maximum pressure so the optimum powder choice always stays within a fairly narrow band of burning rates for whatever case volume you are working with.
I once loaded a .357 with H4831 just to see what would happen...and not much did! This is obviously WAY too slow for the cartridge and despite me filling it to compression it barely went 'pop' and though the bullet did make it out of the barrel it had so little power it bounced off the wood target backer. So in that case you need to go faster on the powder until you balance the amount you can fit with the amount of pressure you're allowed. See? It's basically a simple thing that is complicated by so many choices which is where the various loading manuals will guide you to appropriate powder choices and save you a lot of time.
But..trying to simplify: There are a couple different ways you are limited with your powder selection...the first by chamber pressures. A small amount of very fast burning powder can make the maximum allowable pressure but won't deliver great performance because it's done burning so quickly that in a long rifle barrel it stops pushing before the bullet leaves the tube. A greater amount of slower burning powder can make the same maximum pressure but does it more gradually and pushes longer so the velocity attained will be greater in a longer barrel. This continues until you start to run into the other constraining factor which is the capacity of the case. Using too slow a powder will fill the case to the brim without being able to attain maximum pressure so the optimum powder choice always stays within a fairly narrow band of burning rates for whatever case volume you are working with.
I once loaded a .357 with H4831 just to see what would happen...and not much did! This is obviously WAY too slow for the cartridge and despite me filling it to compression it barely went 'pop' and though the bullet did make it out of the barrel it had so little power it bounced off the wood target backer. So in that case you need to go faster on the powder until you balance the amount you can fit with the amount of pressure you're allowed. See? It's basically a simple thing that is complicated by so many choices which is where the various loading manuals will guide you to appropriate powder choices and save you a lot of time.
Nature Boy
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I started out reloading .308 for my M1A and really focused on burn rates due to the gas operated action. I started with a chart I found on the internet and made a spreadsheet out of it.
Then I researched everything I could find about what folks were using for the M1A. I made a band of powders that followed the conventional wisdom regarding what was safe, then highlighted what people were using. Dark Green for 'preferred' and Light Green for 'lessor used'. Anyway, take a look at it and see if it makes sense. It goes top/faster to bottom/slower
Theoretically, everything in the Orange band should be safe. If I didn't highlight it in Green it was because I couldn't find anyone mentioning it as being used for the M1A
Then I researched everything I could find about what folks were using for the M1A. I made a band of powders that followed the conventional wisdom regarding what was safe, then highlighted what people were using. Dark Green for 'preferred' and Light Green for 'lessor used'. Anyway, take a look at it and see if it makes sense. It goes top/faster to bottom/slower
Theoretically, everything in the Orange band should be safe. If I didn't highlight it in Green it was because I couldn't find anyone mentioning it as being used for the M1A
I was wondering how benchmark, h322 and h335 compared. my concern is I want a good fast accurate varmint load but also want to be safe and not shoot out my barrel either.
I also see things such as that powder is too slow for a 55gr bullet so use this. or you should use a 69gr bullet with that powder cause its best.
I almost attained one hole 5 shot group with benchmark the other day but have been using h335. just trying to help make a decision.
I also see things such as that powder is too slow for a 55gr bullet so use this. or you should use a 69gr bullet with that powder cause its best.
I almost attained one hole 5 shot group with benchmark the other day but have been using h335. just trying to help make a decision.
Nature Boy
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There's a lot of folks using Benchmark for .223. One of my friends favorite for 68-69 is Benchmark. The general rule applies, use the published load data for the powder, never starting at max.
I was worried about shooting 110g VMAX .308 at 3,200 FPS out of my FN SPR and it's affect on barrel wear, but I believe it was Walkalong who reminded me of this fact:
Barrels are a wear item. When it's used up, buy a new one
I was worried about shooting 110g VMAX .308 at 3,200 FPS out of my FN SPR and it's affect on barrel wear, but I believe it was Walkalong who reminded me of this fact:
Barrels are a wear item. When it's used up, buy a new one
Cheesemaker
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Benchmark, H322 and H335 are all close in burn rate - the Hodgdon chart:
https://www.hodgdon.com/PDF/Burn%20Rates%20-%202015-2016.pdf
The weight of the bullet comes into play when it starts to move. Heavier bullets tend to take longer to start move than lighter ones. Couple this with powder burn rates and you start to see how the interact.
Rule of thumb (loosely) - a heavier bullet with a faster powder will have higher pressures than a lighter bullet with a slower powder.
And then there is the barrel length - as RecoilRob explained.
https://www.hodgdon.com/PDF/Burn%20Rates%20-%202015-2016.pdf
The weight of the bullet comes into play when it starts to move. Heavier bullets tend to take longer to start move than lighter ones. Couple this with powder burn rates and you start to see how the interact.
Rule of thumb (loosely) - a heavier bullet with a faster powder will have higher pressures than a lighter bullet with a slower powder.
And then there is the barrel length - as RecoilRob explained.
Well said.
I feel too many reloaders, especially new reloaders, get their shorts in a wad worrying about burn rates. The technicians and scientists at the labs do all the work for you and all you have to do is read the information printed in the data from reputable sources.
Short of understanding that handgun sized cartridges use faster burning powders and as the cases get bigger going into the rifle area, the powder burn gets slower, there is not much use for burn rate for the reloader.
One, the burn rate listing from different sources will frequently be listed in a different order.
Second, the effective burn rate between two powders in two different cartridges can be different. One powder may show faster burn characteristics than another powder in one cartridge but the rates may be switched in a different cartridge.
When looking at the burn rate charts, keep in mind the rates are relative. Looking at the Hodgdon chart (for which Cheesemaker has already supplied the link) we see that IMR4198 is listed as "faster" than IMR3031, but how much "faster" is 4198 than 3031? The table doesn't tell you that.
Nature Boy
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Hey, lets be honest here, we get our shorts in a wad over more that just that
Jim Watson
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My only use of burn rate charts is to answer "What the heck is that stuff?"
So if I see a can of Vectan Tu 5000, I can look to see that it is in between Varget and 4320 and know that it might be worth trying in a medium expansion ratio rifle cartridge like .308.
So if I see a can of Vectan Tu 5000, I can look to see that it is in between Varget and 4320 and know that it might be worth trying in a medium expansion ratio rifle cartridge like .308.
Blue68f100
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Depending on the year of the chart and who published it you will find that they seam to move around. I've seen as much as 5 positions for powders know to be the same. It's just a reference and that all. All the powders have different pressure curves and peaks. Even if there nest to each other. Once may peak before the other and may generate the same pressure.
Burn rates are a very unreliable way to choose a powder. Burn rate charts rarely show powders in the same order and very often the same manufacturer will change the powder positions on their charts from year to year. If you want proof of their unsuitability for safe powder comparisons simply read the burn charts carefully, you will usually find a warning somewhere on the chart that tells you to not use the burn rate chart for selecting a reloading powder. For example, the Accurate powder's chart states;
"Burn rate charts can never reflect the differences between powders in the correct proportion, and can only place powders in approximate burn rate envelopes.
NEVER USE THESE TO DETERMINE/CALCULATE LOADS - ALWAYS REFER TO REPUTABLE LOAD GUIDES/MANUALS."
Manufacturers most often test burn rates by performing a closed bomb test. A measured amount of powder is deposited in to a closed metal container and ignited. Instrumentation measures the pressures, temperatures, and burn time. There are no universal standards for this test and variations in ambient temperatures, barometric pressures, volumes, etc. will cause the results to vary, this is why burn rate charts from different sources will not match. Also, no two batches/lots of the same powder will burn exactly the same, that's why the manufacturer of a specific powder will move the position of their powder relative to other powders from time to time. Put all of these uncontrollable variations together and you can see why burn rates are a poor yardstick.
But for the layman burn rate charts are better than just guessing although I'd recommend reading the manufacturer's recommendations and their reloading information as a primary guide as to what is safe. If the manufacturer doesn't show powder charge information for the cartridge you are trying to build then I'd avoid using that cartridge combination - unless you have verified/first hand knowledge that the load will work. For example, Hornady shows a load using their 110gr Vmax bullets over IMR 4198 for the .308 Win but it's not listed in their Service Rifle section, but I've used that load in my M1As for years with no issues (and it's a very accurate load). While it's not recommended by Hornady I've found no reason to not use it.
I use QuickLoad to help develop my loads. One guideline I like to use is the amount of the usable case volume that the powder uses - the filling percentage. I wont use a powder that will result in less than 50% filling. Years ago IMR came to the conclusion that .30 cal rifles seem to work best when the usable volume is filled to between 93% to 98% and I try to use that guideline for just about everything that I load, including pistols. High fill volumes will prevent you from getting double powder drops and I subscribe to the theory that it prevents unexpected pressure spikes due to unreliable flame front progression through the powder charge. There are powder choices that will work but result in low fill volumes and I'd avoid them. I also avoid compressed powder charges, especially with ball powders. I don't crimp and a compressed charge can push the bullet out of the case which can change everything about the cartridge.
"Burn rate charts can never reflect the differences between powders in the correct proportion, and can only place powders in approximate burn rate envelopes.
NEVER USE THESE TO DETERMINE/CALCULATE LOADS - ALWAYS REFER TO REPUTABLE LOAD GUIDES/MANUALS."
Manufacturers most often test burn rates by performing a closed bomb test. A measured amount of powder is deposited in to a closed metal container and ignited. Instrumentation measures the pressures, temperatures, and burn time. There are no universal standards for this test and variations in ambient temperatures, barometric pressures, volumes, etc. will cause the results to vary, this is why burn rate charts from different sources will not match. Also, no two batches/lots of the same powder will burn exactly the same, that's why the manufacturer of a specific powder will move the position of their powder relative to other powders from time to time. Put all of these uncontrollable variations together and you can see why burn rates are a poor yardstick.
But for the layman burn rate charts are better than just guessing although I'd recommend reading the manufacturer's recommendations and their reloading information as a primary guide as to what is safe. If the manufacturer doesn't show powder charge information for the cartridge you are trying to build then I'd avoid using that cartridge combination - unless you have verified/first hand knowledge that the load will work. For example, Hornady shows a load using their 110gr Vmax bullets over IMR 4198 for the .308 Win but it's not listed in their Service Rifle section, but I've used that load in my M1As for years with no issues (and it's a very accurate load). While it's not recommended by Hornady I've found no reason to not use it.
I use QuickLoad to help develop my loads. One guideline I like to use is the amount of the usable case volume that the powder uses - the filling percentage. I wont use a powder that will result in less than 50% filling. Years ago IMR came to the conclusion that .30 cal rifles seem to work best when the usable volume is filled to between 93% to 98% and I try to use that guideline for just about everything that I load, including pistols. High fill volumes will prevent you from getting double powder drops and I subscribe to the theory that it prevents unexpected pressure spikes due to unreliable flame front progression through the powder charge. There are powder choices that will work but result in low fill volumes and I'd avoid them. I also avoid compressed powder charges, especially with ball powders. I don't crimp and a compressed charge can push the bullet out of the case which can change everything about the cartridge.
The main thing you need to know is they are both well suited to .223.
If you used IMR-4198/ in a 7MM Mag, you would not be able to get max velocity because the pressure curve is too steep (Fast), and it would be easy to blow it up if not very careful. (A case full.)
If you use IMR-4831 you would be able to fill the case and get the most out of it, because the pressure curve is less steep (Slower) and you can use more powder without exceeding max pressure.
Make sense.
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spitballer
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I've been reloading for years and I'm still learning about burn rates! In the end I simply have to agree that most of the hard work has been done for us, and published load data is the place to start. I mean, when you factor in all the factors like barrel length, twist rate, bullet hardness, etc. it's truly mind boggling, at least to me it is, and I'm grateful to the manufacturers that have gone the extra mile and published guidelines for using their products. One of the basics I remember from the Civilian Marksmanship program was that target ammo uses faster powder and travels slower, while high-velocity ammo uses slower powder and travels faster. This may be over-simplifying but I've always tried to keep it in mind when shelling out big bucks for yet another can of powder. FWIW Lee's reloading book discusses theories regarding powder speed and powder selection, and presumably other manuals do also.
The only real use I have ever made of the burn rate charts has been in picking between loads in cases where the manual was developed using a different barrel length than I am using.
For example, the data Hodgdon's provides online for .223 Remington was developed using a 24 inch barrel. If my rifle has a 16 or 18 inch barrel, I may choose to start developing a load around one of the faster burning powders like IMR3031 versus a slower burning one like IMR4320. In any case, all it does is guide my selection of a starting point.
My rationale for gravitating towards a faster powder in a shorter barrel when the load was developed in a longer barrel is that I believe the faster powder is more likely to be closer to the performance in the load data.
For example, the data Hodgdon's provides online for .223 Remington was developed using a 24 inch barrel. If my rifle has a 16 or 18 inch barrel, I may choose to start developing a load around one of the faster burning powders like IMR3031 versus a slower burning one like IMR4320. In any case, all it does is guide my selection of a starting point.
My rationale for gravitating towards a faster powder in a shorter barrel when the load was developed in a longer barrel is that I believe the faster powder is more likely to be closer to the performance in the load data.
Unfortunately it doesn't work that way. You will still get more velocity with the slower powder in the shorter barrel.
Fast and slow is relative. They are all very, very, fast, some are just slower than others.
Fast and slow is relative. They are all very, very, fast, some are just slower than others.
RecoilRob
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A while back I was doing some checking on suitable loads for a KelTec PLR-16 which has all of a 9" barrel, and darned if the fastest loads using the heaviest charges of slowish powder in 24" barrels were also coming out of the little 9" the fastest too! Seems the majority of velocity has been gotten by the time it moves that far and the only thing I really noticed by changing powders was the concussion of the muzzle-blast did seem to be a bit less using a quicker powder such as RL-7 vs H335 for example which makes a freaking basketball sized orange flash.
Another consideration is the economy of loading: if 21 grains of RL-7 (going from TopOfHead..do not duplicate!) will do the job....you save some cash over using 26-28 grains of the really slow stuff. As mentioned you MUST watch the case filling!! Slow rifle powder sloshing around inside a large case can and will do weird things when it's lit...and can become a bomb under certain circumstances that are best to be avoided.
One fellow was loading some reduced loads for an old rifle *that I can't remember..but it's unimportant* and knew darn well to elevate the muzzle before slowly bringing the loaded rifle down to shoot to position the powder back against the primer. He fired many, many of these and all went according to plan until he let his buddy shoot it once...and forgot to tell him about the powder positioning. Yep...the guy loaded it muzzle down, brought it up to level and BOOM...the thing splintered on him. Keeping the load density to 90% or more is a great way to ensure consistent ignition characteristics and almost mandatory with ball powders IIRC.
Another consideration is the economy of loading: if 21 grains of RL-7 (going from TopOfHead..do not duplicate!) will do the job....you save some cash over using 26-28 grains of the really slow stuff. As mentioned you MUST watch the case filling!! Slow rifle powder sloshing around inside a large case can and will do weird things when it's lit...and can become a bomb under certain circumstances that are best to be avoided.
One fellow was loading some reduced loads for an old rifle *that I can't remember..but it's unimportant* and knew darn well to elevate the muzzle before slowly bringing the loaded rifle down to shoot to position the powder back against the primer. He fired many, many of these and all went according to plan until he let his buddy shoot it once...and forgot to tell him about the powder positioning. Yep...the guy loaded it muzzle down, brought it up to level and BOOM...the thing splintered on him. Keeping the load density to 90% or more is a great way to ensure consistent ignition characteristics and almost mandatory with ball powders IIRC.
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