Accuracy: fast burning powder vs slow burning powder

[Beiruty]

Fast vs slow burning powder and its effect on rife accuracy.

It is well known that for a given case capacity/bullet weight/caliber there is an optimum powder charge/powder burning rate/powder density that would maximize the MV potential of a given rifle.

However, let us focus on the effect of the fast vs slow powder on rifle accuracy.
My observation so far is that fast powder that would generate acceptable MV (say 2-4% less than the maximum possible MV) would generate more accurate loads. That is more so from light barrels than heavy bull barrels.


What do you think?

 

[Jager]

I think if using fast-for-caliber powders were intrinsically more accurate than slow-for-caliber powders... we'd all have empirically come to observe that fact over the many decades handloading has been a thing.

And, yet, we (the royal "we") haven't, at all, come to that conclusion.

The reason is that there is far more to the story.

 

[Beiruty]

More to he story:
1) Fast burning powder has major role in pushing the bullet into the lands faster
2) And, for the next few inches of the bullet travel where the reflective shock waves are critical on the orientation and alignment of the bullet inside the lands. That was theorized by the OBT theory author, Lang, in his paper.
3) By the time the bullet travels closer to the muzzle, the powder has been completely burnt and as a consequence the powder has less effect on the dilation of the muzzle bore at the the of the bullet exit. That should enhance the accuracy (my observation).
4) Light barrels would benefit more than bull barrels from the use of fast burning powder loads tailored for accuracy.

 

[jelenko]

Fast vs slow burning powder and its effect on rife accuracy.

It is well known that for a given case capacity/bullet weight/caliber there is an optimum powder charge/powder burning rate/powder density that would maximize the MV potential of a given rifle.

However, let us focus on the effect of the fast vs slow powder on rifle accuracy.
My observation so far is that fast powder that would generate acceptable MV (say 2-4% less than the maximum possible MV) would generate more accurate loads. That is more so from light barrels than heavy bull barrels.


What do you think?

Not sure what you are wanting to compare.
Are you wanting to compare a faster burning load that is near max pressure vs a slower burning load that is near max pressure? And, are you thinking the loads would be tuned to the rifle?

 

[jelenko]

And, for the next few inches of the bullet travel where the reflective shock waves are critical on the orientation and alignment of the bullet inside the lands. That was theorized by the OBT theory author, Lang, in his paper.
3) By the time the bullet travels closer to the muzzle, the powder has been completely burnt and as a consequence the powder has less effect on the dilation of the muzzle bore at the the of the bullet exit. That should enhance the accuracy (my observation).

The speed of the compression waves in steel is around 10,000 fps - much faster than the bullet travels => the bullet is going to see these waves more than once as the bullet travels down the barrel.

The % of powder burned is not what would affect deformation of the barrel - only the pressure.

 

[Beiruty]

Not sure what you are wanting to compare.
Are you wanting to compare a faster burning load that is near max pressure vs a slower burning load that is near max pressure? And, are you thinking the loads would be tuned to the rifle?

1) Assuming both powders charges are near max Pressure as you stated.
2) Assuming both powders' loads can be tuned for a given rifle
3) I would like to compare fast vs slow-burning powders. And, find out if the use of fast-burning powders would produce more accurate loads than slow-burning powders loads

 

[Beiruty]

...
The % of powder burned is not what would affect deformation of the barrel - only the pressure.

The rate of burning powder would correlate with fast decaying pressure behind the bullet near the Muzzle.
Fast burning powder ---> fast decaying pressure behind the bullets near the muzzle.
Slow-burning powder ---> slower decaying pressure behind the bullets near the muzzle.

 

[Beiruty]

243 87-gr V-max under RL23 (slow burning rate) Muzzle Pressure 15550 PSI

 

[Beiruty]

243 87-gr V-max under Hodgdon Varget (fast burning rate) Muzzle Pressure 13340 PSI

 

[Beiruty]

Fast vs Slow powder reduced the Muzzle Pressure by 14%

 

[darkangel_r2]

More to he story:
1) Fast burning powder has major role in pushing the bullet into the lands faster
2) And, for the next few inches of the bullet travel where the reflective shock waves are critical on the orientation and alignment of the bullet inside the lands. That was theorized by the OBT theory author, Lang, in his paper.
3) By the time the bullet travels closer to the muzzle, the powder has been completely burnt and as a consequence the powder has less effect on the dilation of the muzzle bore at the the of the bullet exit. That should enhance the accuracy (my observation).
4) Light barrels would benefit more than bull barrels from the use of fast burning powder loads tailored for accuracy.

From observations I have made its a question of signals in vs signals out. There are other factors at play but this is a big one.

The more consistent and sharp your peak pressure curve is the more consistent your barrel vibrations will be. The faster the powder burn rate generally the sharper the peak. This is the input signal into your barrel. Since you are in gordons I think having your z1 (max surface area lit/ fastest gas production) line up near or just before peak pressure also helps this happen. An elongated pressure peak (slower burning powders) puts in a more confused signal into the barrel to start vibrations.

Having all powder burned before barrel exit also helps keep your velocity spreads low. The earlier the burn out and more consistent your pressure profile (good ignition, pressure curves tight on top of each other) the tighter your es/sd numbers will be in general.

One thing to keep in mind is that barrel vibrations are developing from rest. They start at zero amplitude and build up to max amplitude. So the faster the bullet the lower amplitude vibrations you will be dealing with. This is generally a good thing. It is especially a good thing for close range accuracy.

Bore size also contributes. 60k psi in a 308 bore has a ton more force acting on the barrel than 60k psi in 6mm or 5.56 as force from pressure on an object is applied via its surface area. You can get away with a lot less metal in the barrel and still have an accurate rifle with small calibers.

It will depend on the amount of metal you have around the crown weather muzzle pressure is a factor or not. Pencil profile with magnum powders might be an issue. Strait taper with 6mm ppc powders not likely an issue lol.

Bullet weight also has a huge input on timing regardless of powder used. A 6.5 creed with a 144 berger and a 123 lapua have very different exit times even with the same powder.

 

[mikecr]

Burn efficiency is apparently better with higher powder percentages burning in or closest to chamber.
I speculate that slower powder burning further down a barrel adds to bullet mass and varies more in burn rate. I also believe high muzzle pressure is detrimental to clean bullet release.

I can't prove this.

 

[Homerange]

3) By the time the bullet travels closer to the muzzle, the powder has been completely burnt and as a consequence the powder has less effect on the dilation of the muzzle bore at the the of the bullet exit. That should enhance the accuracy (my observation).

In the absence of a decent crown that indeed might be valid however there are other things to consider with fast vs slow powders.....throat erosion.

 

[K22]

I don't think there are any absolutes when it comes to this issue if we are focused solely on accuracy.

A lot of the work has already been done if you are shooting well established traditional calibers - i.e., proven loads that work fairly regularly with certain calibers. Starting with powders that have a history of performing well with certain caliber / bullet combo's is a good place to begin. I don't think you have to revent the wheel so of speak.

Generally, I've found that the faster powders tend to work better with lighter bullet and the slower powders with heavier bullet but it's not absolute. My 243 Win Browning X Bolt shoot H4895 w/ the Sierra 85 BTHP better than either IMR 4064 or IMR 4350 which totally surprised me. The only reason I tried H4895 was that I had a lot of it and couldn't get the other mentioned powders. I was stunned by the results. Thus it goes to show that nothing is absolute.

Magnum cartridges tend to do better with slower powders but you have to have sufficient length of barrel to take advantage of the slower powder. I never understood cutting the barrel down under 24 inches for a magnum cartridge. 26" is ever better. Most don't buy a magnum for accuracy per se but for the extra energy that they feel is needed.

In my opinion, let the rifle tell you what it likes. Unforturnately with today's shortages, extensive load testing can be problematic. That's why I'd start with something that has a solid reputation for performance with a given bullet / cartridge combo but don't be afraid to try something new if that approach doesn't produce the results you need.

 

[RegionRat]

It is well known that for a given case capacity/bullet weight/caliber there is an optimum powder charge/powder burning rate/powder density that would maximize the MV potential of a given rifle.

Is this really an “optimum” or driven by several material limits in the brass, steel, and bullets?

For example, if the safety margins on the cartridge case could be violated, wouldn’t we search for the next higher accuracy node? We would stuff more energy into the case and keep on going until something else failed or we lost accuracy by going faster. Regardless of the powder burn speed.

So, I’m just playing Devil’s Advocate here, but I don’t think we can say there is an optimum recipe for accuracy since there is no standard barrel length or profile for a given caliber. Maybe there could be an argument for this if we narrowed the discussion to a specific example like say a Palma bbl design. Even then, the load manuals list a wide range of powder speeds and you probably wouldn’t get everyone to agree that just one or two of them was an “optimum”.

My observation so far is that fast powder that would generate acceptable MV (say 2-4% less than the maximum possible MV) would generate more accurate loads. That is more so from light barrels than heavy bull barrels.

Maybe we should again narrow this down. What is the specific observation? Is this a generality we would all agree with or one that would be a debate?

If we walked down the lines at some major BR or F-Class competitions, we would certainly see some statistics for a few things that tend to show a theme, but would we really say that there is an obvious pattern to accuracy?

Sometimes, there is a survey where the attendance is invited to list their equipment and details of what they are shooting. If we started with a list like that and narrowed the discussion to a few examples of the top finishes in some well attended matches, we may be able to have a better discussion based on actual values and observations with the assumption that those competitions drive some sort of “optimum” of accuracy. Then maybe we could look at the differences in powder or burn rate and see if any of the theory holds up.

 

[darkangel_r2]

Maybe we should again narrow this down. What is the specific observation? Is this a generality we would all agree with or one that would be a debate?

If we walked down the lines at some major BR or F-Class competitions, we would certainly see some statistics for a few things that tend to show a theme, but would we really say that there is an obvious pattern to accuracy?

Sometimes, there is a survey where the attendance is invited to list their equipment and details of what they are shooting. If we started with a list like that and narrowed the discussion to a few examples of the top finishes in some well attended matches, we may be able to have a better discussion based on actual values and observations with the assumption that those competitions drive some sort of “optimum” of accuracy. Then maybe we could look at the differences in powder or burn rate and see if any of the theory holds up.

If we are talking about raw accuracy (correct me if I'm wrong) I'm not sure if there is a current 100 yard world record that's using a powder slower burning than v133.

 

[RegionRat]

@darkangel_r2 that illustrates part of my point.

There are some patterns to what we are calling state of the art accuracy performance, but there may or may not be agreement when we throw in Midrange, Long Range, F-Class, Highpower, etc.

It would even be difficult to get a consensus on what constitutes a "fast" or "slow" powder in a given context.

We can model internal ballistics to a degree, but then it falls to real results to calibrate a model well enough to be able to either mirror those results or go even farther and predict the next ones.

If a particular context gets nailed down to a standard, you can have a decent debate on the concept of which powders will tune for accuracy better than others.... maybe....

 

[Ned Ludd]

FWIW - the originator of OBT Theory is Chris Long. You will find a wide range of responses here regarding his longitudinal barrel shock wave theory as an explanation for OBT Nodes, even from those that generally believe those nodes exist, such as myself. What I'm getting at is that your premise about using faster powders is based, in part, on the theory of longitudinal barrel shock waves and how they might affect dilation of the bore at the muzzle, and it is not even widely accepted that this theory is the correct explanation for the existence of OBT Nodes. This theory is certainly not written in stone. For that reason, I wouldn't get too far down in the weeds ruminating about this.

In terms of optimal precision, what I can tell you is that I have observed on more than one occasion that I have gotten the best precision in a given load using powders that were only just slightly faster than what might be considered optimal for a given bullet weight/caliber. I know a few other people that have had the same experience. An example of this would be the use of H4895 in the .223 Rem with heavy (90-95 gr) bullets. Although only slightly faster than Varget, H4895 in my hands has given noticeably better results, time and time again. Unfortunately, I cannot tell you exactly why this is, I can only tell you that I have observed this behavior. There may be some rational scientific explanation, or it may be as simple as that Varget is just a little "slow" for the barrel lengths/bullet weights I am using, rather than that H4895 is slightly "fast". We generally might have a few different powders from which to choose within a given burn rate for a particular cartridge/bullet/barrel length combination. Within that window, it is likely that more than one powder might provide acceptable precision, if we were actually able to test all of them. Any differences observed between powders that all fall within an "acceptable" burn rate window might easily be due to some factor or intrinsic property of the powder beside than the actual burn rate. Trying to understand and/or quantify such differences is going to be a tough row to hoe. The alternative is simply to test different powders and determine empirically which works best in a given load. Of course, we always want to know "why", but often must settle "what works" without any true explanation. I think this is likely to be one of those cases.

 

[mikecr]

With a 6PPC I don't think you would find anything competitive with a powder much slower than N133.
But this is not purely about burn speed in a ~22" barrel. I believe most of it is about delving in competitive pressures (which are not viable in larger cartridges). Diminished returns of pressure, providing diminished variance of returns. This is possible with such a tiny little chamber.
Similar is available with an overbore 30br.
They get you to 300yds

The potentials with this approach would logically ramp downward as cartridge capacity goes upward.
Viable max pressures continually fall with chamber area.
Given this, I think it's prudent to go no more in capacity than needed.
Example:
With a choice of 260AI -vs- 6.5x284, for ~140gr bullets, I would go 260AI running way less and faster powder.
For 123-130gr bullets I would choose 6.5x47L for the same reasons.
To run 123gr bullets in a 6.5x284, would seem unnecessarily challenging to best precision. And there is just no good reason to do it. Now there is probably someone out there shooting the combo like crazy, but I doubt it would be a majority trend.

 

[jackieschmidt]

If you look at the way many of us shoot a 6PPC, 133 is actually too slow.

When you are using a 12 inch long drop tube with a slow trickle to get it all in there and still have room for a bullet, common sense says,……Why don’t you got to 130, or 4198, or 2015, etc.

The answer is, it won’t agg as well.

keep in mind, what we call a medium load is still considerably hotter than what any civilian loading manual would consider maximum.

so, in this case, the slower powder for the case volume wins out.

As a note, I have seen one instance where a shooter used a powder considerably slower than 133 to win a National Yardage. It is a great Benchrest Story.

It was in the mid 2000’s, and we were at Kansas City for the NBRSA Nationals. The last yardage was the Heavy Varmint 200 on Saturday morning. Larry Bagget had been struggling with vertical, and announced that he was going to try something that was to put it mildly, different.

He went to a local gun store and bought a pound of 4895. He then went to a hardware store and got a .080 drill. He drilled the flash holes out on about 15 pieces of brass and then loaded them to the top with the 4895. He was shooting his own 68 grn bullet.

Well, he wasn’t going to win small group with that load, but that rifle consistently shot nice round 4 tenths groups all morning in some tough conditions, and ole Larry won that yardage with around a .220 agg.

I have always thought that was a neat story, and I got to see it Happen.