ES of slower powders

[PigButtons]

If this were other types of propellants, a term would get thrown around that for some reason isn’t associated with loading cartridges, “volumetric efficiency”. If we are talking about an engine, it was determined that 14.7/1 is the magic air fuel ratio for best performance. The computer and sensors have the job of maintaining that ratio in all conditions. A very basic look.

This is no different than loading at the bench for conditions, but without the computer and information inputs, it’s more art than science.

What I think I have found over the years, is that with many powders you can find a fill ratio that is most efficient. Meaning that if 98% produces the smallest ES/SD, you can move the bullet almost anywhere you want and if you keep that fill ratio, the spreads stay consistent. That ratio, determines initial burn rate and start pressures. If start pressures are consistent, they should be consistent all the way down the barrel, leading to consistent exit times and velocity.

The trick is getting that exit time where you want it. A “0” SD at the wrong exit time could be a lot of vertical.

What you are doing with seating depth or small powder adjustments is fine tuning that volumetric efficiency, manipulating the burn rate to its most efficient or consistent point in that particular chamber and day.

In an effort to prove a point that burn rates can be manipulated to extremes with case capacity and bullet weight, I used sub sonic 300 Blackout. 10.5 grains of 4227 under a 208 AMax that netted 1050 fps. In the same rifle, 11.5 grains under a 125 SST nets 1075 fps. and still has enough pressure to cycle an AR.

Being able to tune gas pressure in a load enough to cycle a gas gun, or not, simply by changing seating depth, changed my thinking about manipulating pressures and therefore burn rates.

So in my mind(as twisted as it can be), a high density load of a slow powder, may just actually have a faster burn rate, than a low density load of a faster powder. Where this will show on the target is different exit times at the muzzle. It’s possible to have the exact same velocity, with completely different travel time from chamber to muzzle. It’s all based on acceleration curves.

Just some different observations

I really like the "volumetric efficiency" in a gas Internal combustion engine analogy. Makes perfect sense to me. Burn rate ~ octane: Fill % ~ compression ratio: Bullet weight ~ reciprocal mass: Case shape ~ Fuel Flow Path. Get them all tuned to each other and you get consistent power.

 

[INTJ]

I still hold to ES doesnt matter even for hunting, and I tune a lot more hunting rifles than BR. If you dont test the rifle at the distance you plan to take game, you really shouldn't be shooting game that far then. But I get your point and I agree with you as well. My point is the load should be tested at the distance and as Leo said, "the paper doesn't lie"

I should clarify. By finding a load a close range and then making hits at long range I am referring going out and shooting gongs or rocks. So I agree that the max distance we plan to shoot game should be tested before taking such a shot. It isn't so critical inside of 500 yds, but at long range it's very critical.

I'll bet that those hunting loads you found that shoot well at 1000 yds have a fairly low ES. That is the advantage of load development at that distance.

Last week I did chrono some loads that I shot at 1000 yds. I checked four seating depths. Three shots of each seating depth shot round-robin for a ladder. The seating depth with the least amount of vertical had the lowest ES. I have no idea if that's always the case. In fact, I don't expect it to be. Still, it was interesting.....

 

[JohnKielly]

Twenty years back I started competing in a discipline shot only in Great Britain & Australia called Match Rifle which uses the .308 Winchester caliber over distances of 1000, 11000 & 1200 yards. I've inevitably found that loads that work consistently over all three distances are those with the lowest ES. Further, I've found that of the powders that work in a chamber throated way out beyond SAAMI to maximise the velocity of 210 & 215 Bergers & satisfy ES (Vargey, Reloader 17, N150 for example), the one that has always worked for me is the one with the smallest granulation, N550.

 

[Mulligan]

Surface area to volume ratio likely has a lot to do with ignition of powder. I believe this based on my experience and education in fire science.

When we teach a rookie school for wildland firefighters, we go through a short section on Probability of Ignition, during this section, we ask the students to ponder or visualize the effort it would take to ignite a ton on fuel. In this case, a one ton section of a large tree the trunk of which is lying on the ground, no brush or fine fuels around it. The other, a one ton bale of straw scattered 6" deep over a large area.
Which would be ignited easier if you were standing there flicking lit matches at them? This exercise really helps the students understand the concept of, surface area to volume ratio. They are both one ton of fuel, but are arranged much differently. That arrangement has a strong effect on ignition potential.

Now think about this, the same bale of straw, all fluffy scattered about the ground in a uniform 6" layer and another tightly bailed, bail of straw sitting is a bare dirt patch. The fluffy straw would ignite and spread much faster than the tightly compressed bail. It is the same amount and type of fuel, yet if both are ignited at the same time, one will quickly be consumed, the other, will smolder for days. Of course the fastest and slowest powders are much closer in burn rates than the straw example given, but I think there are similarities worth considering.

In wildland fire, we describe fuels as 1 hour, 10 hour, 100 hour, 1000 hour, and 10,000 hour time-lag fuels. This refers to the length of time it takes for the moisture content of the air to normalize with the fuel in the forest. The one hour fuels are dry grass and leaves and very small twigs. It would take one hour for the fuel to dry out as the day heats up. In other words, if you have 50% RH and 50 degrees (F) in the AM and the day heats up to 15% RH and 90 degrees, the fine fuels are about 1 hour behind the actual temp and RH changes, the heavier fuels could be months behind, therefore following seasonal trends and not daily or hourly trends. Powder is likely ( although I have performed some small tests on this, nothing worth sharing yet) a fuel that would respond in minutes, not hours. Think of the short range benchrest shooters who have used a particular powder and got a good load worked up loading at the range. Then the heat of the summer shows up and they go out with their good load and in the morning it works great. Then in the heat of the afternoon, they cannot adjust the powder thrower fast enough to stay ahead of the changes in the powder as they try to keep the tune.

Temperature in the case effects ignition, each fuel ( grass, trees, house shingles, and in this case, powder) has a "temperature of ignition". The fuel is heated to ignition temperature and at that point it is releasing a gas that burns. Until then, it is a heat sink. In other words, the energy cannot be released until the fuel is heated and the gases ignited.
If the heating and ignition of the fuels is not relatively consistent, I suspect it would be very difficult to have uniform extreme spreads. Given differences is primer weights, differences if kernel size of powder, and the host of other variables we cannot control, I find it amazing we see the uniformity we do see.

My best guess is, there may be a optimum temperature range where the bigger stick powders actually have a better (better in this case would be smaller) extreme spread?

CW

 

[Northridge]

I see this slightly different than my friends @Alex Wheeler and @Northridge.

We 1000yd BR shooters have a habit of saying ES doesn't matter, and many of us don't even use a chronograph when tuning at 1000 yds. I know I typically don't. It's just one more thing to drag up to the line and I don't need it.

However, whenever I do check my good loads with a chronograph, they are almost always have ES in the single digits or low teens.

So we have to be careful when we say ES doesn't matter. The stuff we do to load for LR BR, the case sorting and prep, primer sorting, bullets sorting, etc is going to minimize ES. I don't know if any of my LR BR loads, even my initial loads at short range, have ever had an ES of much more than 20.

A hunting rifle is a different matter, especially when we aren't able to shoot it at the distances we will hunt. I have seen sub 1/2" 100 yd groups with ES of 50 or more. I can promise that load won't shoot well at long range.

I and many others have had a lot of success finding a load at 100 yds, then making hits past 1000 yds. To do that, we have to find a load that shoots small AND has a decent ES. The priority is groups size, but the ES ought to be around 20 or less.

Now if we are doing load development at 1000 yds for a hunting rifle, then ES isn't a focus--because we won't have good groups or tuning ladders at 1000 yds if we have a bad ES.

I agree in part, there is a cut off but saying they simply do not matter is not what I try to convey. what I try to point out is this when you are are in a zone where rifle wants to shoot often the SD's in the 0-4 will simply be in a moment of move, shift or quadrant change and it will shoot bad but its counter a tenth or two back will have SD's in th 8-12 range but will hold indifference +- velocity in a competitive lump with zero stringing or popped shots. when i use a chrono graph what I most am looking for is not a velocity window sort of documenting velocity but how poorly the SD's correlates with good grouping. if the natural grouping aligns with 0-SD's great but in all honesty im more troubled when I document this. A tune that will "natural" ladder small and have slightly larger SD"s actually excites me.. what I mean by Natural is a platform that is not manipulated by tuner or muzzle brake but naked if you will. Now as of late I have spent a lot of time in the shadows tinkering with tuners and one of my biggest things to test was taking a known tune that simply produces low SD's but shitty grouping and bend or align frequency until it aligns with tune window making it good. well one thing I discovered was this is possible forcing rifle in to tune but the window was still narrow and un- forgiving or finicky. will it work in a pinch? yes but still not reliable day to day as the tuner is still fighting "natural" frequency in a custody battle. this is not a dig on tuners as they are a device that can make a situation cleaner but not always as I have discovered. but it does still evolve around a usable or except-able velocity SD with "stiffer barrels" now lets talk hunting tapers from about #6 contour down light weight barrels can manage "huge" SD's and shoot really small at distance, sometimes in short 3 shot clusters as small as any good bench gun at 1000 yard. documenting or realizing barrel compensation out of a light barrel is un matched as well as great grouping with massive SD's

Shawn Williams

 

[Alex Wheeler]

I agree Shawn. And in my experiance, not just with personal rifles but the many that I help tune or get feedback on, Id say the best grouping and lowest es loads never line up. I mean, I can remember it ever happening. Usually its close but just off of on the powder charge. I think if I had to tune based on nothing but ES numbers, I would pick a load with 12-15 ft. of es. The hunting stuff is usually a little closer to 20. You can make them go single digit but the groups open up. It does not make sense but how many times do you have to see it play out to believe it?

 

[KMart]

Surface area to volume ratio likely has a lot to do with ignition of powder. I believe this based on my experience and education in fire science.

When we teach a rookie school for wildland firefighters, we go through a short section on Probability of Ignition, during this section, we ask the students to ponder or visualize the effort it would take to ignite a ton on fuel. In this case, a one ton section of a large tree the trunk of which is lying on the ground, no brush or fine fuels around it. The other, a one ton bale of straw scattered 6" deep over a large area.
Which would be ignited easier if you were standing there flicking lit matches at them? This exercise really helps the students understand the concept of, surface area to volume ratio. They are both one ton of fuel, but are arranged much differently. That arrangement has a strong effect on ignition potential.

Now think about this, the same bale of straw, all fluffy scattered about the ground in a uniform 6" layer and another tightly bailed, bail of straw sitting is a bare dirt patch. The fluffy straw would ignite and spread much faster than the tightly compressed bail. It is the same amount and type of fuel, yet if both are ignited at the same time, one will quickly be consumed, the other, will smolder for days. Of course the fastest and slowest powders are much closer in burn rates than the straw example given, but I think there are similarities worth considering.

In wildland fire, we describe fuels as 1 hour, 10 hour, 100 hour, 1000 hour, and 10,000 hour time-lag fuels. This refers to the length of time it takes for the moisture content of the air to normalize with the fuel in the forest. The one hour fuels are dry grass and leaves and very small twigs. It would take one hour for the fuel to dry out as the day heats up. In other words, if you have 50% RH and 50 degrees (F) in the AM and the day heats up to 15% RH and 90 degrees, the fine fuels are about 1 hour behind the actual temp and RH changes, the heavier fuels could be months behind, therefore following seasonal trends and not daily or hourly trends. Powder is likely ( although I have performed some small tests on this, nothing worth sharing yet) a fuel that would respond in minutes, not hours. Think of the short range benchrest shooters who have used a particular powder and got a good load worked up loading at the range. Then the heat of the summer shows up and they go out with their good load and in the morning it works great. Then in the heat of the afternoon, they cannot adjust the powder thrower fast enough to stay ahead of the changes in the powder as they try to keep the tune.

Temperature in the case effects ignition, each fuel ( grass, trees, house shingles, and in this case, powder) has a "temperature of ignition". The fuel is heated to ignition temperature and at that point it is releasing a gas that burns. Until then, it is a heat sink. In other words, the energy cannot be released until the fuel is heated and the gases ignited.
If the heating and ignition of the fuels is not relatively consistent, I suspect it would be very difficult to have uniform extreme spreads. Given differences is primer weights, differences if kernel size of powder, and the host of other variables we cannot control, I find it amazing we see the uniformity we do see.

My best guess is, there may be a optimum temperature range where the bigger stick powders actually have a better (better in this case would be smaller) extreme spread?

CW

An interesting test for the scientific minded on this subject might be testing H 4831 regular cut vs short cut or IMR 7828 regular vs SSC. Granted there will be lot to lot variation but it is the best examples we have in the powder world.

 

[dnellans]

I dont think anyone understands ES totally. You can take a very good ES load and add .3 of powder and make the ES higher. You can also effect it with small seating depth changes. I believe its to do with exit timing and muzzle expansion, however have no proof other than I cant explain it any other way. The good news is, ES and group size do not correlate. Shoot groups at the distance you compete or hunt and forget about ES.

Do you not worry about ES -at all- Alex? Or just once it’s within reason you make sure that positive compensation on the load tune takes case of the rest?

Vertical is easy to think about as ES and positive compensation but you actually said “group size”, which isn’t just vertical either. Any thoughts on vertical vs horizontal?

 

[taylorw]

I agree with Alex.. Ive done a fair amount of testing with the correlation between ES and tuning past that ~850 range since 2012 and can say, without a doubt, my best tunes, more times than not, fell between 10-15 ES with the most common number for a given load being 13ES.
I usually have vertical when the load is running in that mid single digit range and looking at the target, it’s usually in the area where your just coming into your tune window (transitioning from the vertical climb to the plateau)
So the way I picture this is if you decide to shoot groups strictly off single digit ES, some shots hit the lower end of the tune window while others drop out into the area where the charges are still climbing the target. At least that’s my take on it anyways..
And as for why the best tune falls in those low teen numbers.. I have no idea other than muzzle position and compensation.

 

[JFrank]

Shawn lost me when he started bending and aligning frequencies.

 

[Northridge]

Shawn lost me when he started bending and aligning frequencies.

Lol, shoot ladders enough and if your willing to agree with what you see time after time doors will open I promise you will witness what I am getting at. some would think there is simply one shock wave, cosign , bell curve etc. and that it happens in a soft delicate round manner, I tend to disagree with this mind set. by manipulating the sign wave and its characteristics when we implement different forces, shock multiple vibrations, heat , stiffer lighter stocks etc. its a marvel for sure. I have opinions on SD's in regard to better grouping so often lines up with lesser SD's as well but maybe some other time..

Shawn Williams

 

[INTJ]

I agree in part, there is a cut off but saying they simply do not matter is not what I try to convey. what I try to point out is this when you are are in a zone where rifle wants to shoot often the SD's in the 0-4 will simply be in a moment of move, shift or quadrant change and it will shoot bad but its counter a tenth or two back will have SD's in th 8-12 range but will hold indifference +- velocity in a competitive lump with zero stringing or popped shots. when i use a chrono graph what I most am looking for is not a velocity window sort of documenting velocity but how poorly the SD's correlates with good grouping. if the natural grouping aligns with 0-SD's great but in all honesty im more troubled when I document this. A tune that will "natural" ladder small and have slightly larger SD"s actually excites me.. what I mean by Natural is a platform that is not manipulated by tuner or muzzle brake but naked if you will. Now as of late I have spent a lot of time in the shadows tinkering with tuners and one of my biggest things to test was taking a known tune that simply produces low SD's but shitty grouping and bend or align frequency until it aligns with tune window making it good. well one thing I discovered was this is possible forcing rifle in to tune but the window was still narrow and un- forgiving or finicky. will it work in a pinch? yes but still not reliable day to day as the tuner is still fighting "natural" frequency in a custody battle. this is not a dig on tuners as they are a device that can make a situation cleaner but not always as I have discovered. but it does still evolve around a usable or except-able velocity SD with "stiffer barrels" now lets talk hunting tapers from about #6 contour down light weight barrels can manage "huge" SD's and shoot really small at distance, sometimes in short 3 shot clusters as small as any good bench gun at 1000 yard. documenting or realizing barrel compensation out of a light barrel is un matched as well as great grouping with massive SD's

Shawn Williams

Shawn,

So are you saying a hunting rifle with a lighter contour barrel, or a carbon barrel, could shoot well at 1000 yds and have a three-shot ES of say 50-60 fps? I have never even tested that as I keep tuning till I have a good group with with an ES 20ish or better.

I have never considered that a lightweight barrel might allow for more positive compensation than a heavy barrel.

 

[Northridge]

Shawn,

So are you saying a hunting rifle with a lighter contour barrel, or a carbon barrel, could shoot well at 1000 yds and have a three-shot ES of say 50-60 fps? I have never even tested that as I keep tuning till I have a good group with with an ES 20ish or better.

I have never considered that a lightweight barrel might allow for more positive compensation than a heavy barrel.

traditional full steel contours yes, carbon fiber is a different cat all together.. I also find light contours perform better often being spanked more from a charge weight prospective, obviously safe pressure being observed on the upper end.

Shawn Williams

 

[gunsandgunsmithing]

Lol, shoot ladders enough and if your willing to agree with what you see time after time doors will open I promise you will witness what I am getting at. some would think there is simply one shock wave, cosign , bell curve etc. and that it happens in a soft delicate round manner, I tend to disagree with this mind set. by manipulating the sign wave and its characteristics when we implement different forces, shock multiple vibrations, heat , stiffer lighter stocks etc. its a marvel for sure. I have opinions on SD's in regard to better grouping so often lines up with lesser SD's as well but maybe some other time..

Shawn Williams

I agree that the sine wave is not a smooth, simple pattern. In fact, I know it's not the case at all. The sine wave is rough and jagged due to several factors, but they can be summarized by saying that there are multiple frequencies traveling up and down the barrel at once, at something near 20,000fps in stainless steel. You can stumble upon a spike along the sine wave when tuning. With a tuner, it's characterized by a tiny group that goes to complete shat with a 1 mark move of the tuner. That said, there is still a dominant sine wave pattern that will give consistent and repeatable group shape on both sides of a sweet spot. That's what you're looking for!!

I see no difference in "forcing" a frequency with a tuner, as opposed to a smaller contour, or longer barrel, ie, less stiff barrel. I see tuners much like changing barrel stiffness without affecting velocity. They leave that up to the load...much like changing bbl length but keeping the same velocity, changing the frequency but not speed of the load. This is how tuners work, by optimizing where the muzzle is when the bullet reaches the muzzle....Timing.

The tuner being at the end of the bbl is adjusting the average of all the frequencies going on at once, behind it.

As to less stiff barrels offering a wider node...I agree. A tuner(mass) at the end of the barrel literally does create more muzzle deflection and a wider arc(amplitude) while the bullet is still in the barrel. That's an interesting statement on its own because physics teaches us that more mass at the muzzle will reduce amplitude. That's true, over time, but in the time we're concerned about, while the bullet is in the barrel, it's not the case at all...making a stiff barrel act like a less stiff barrel in terms of amplitude/muzzle deflection and its affect on tuning.

Interesting discussion, even if it was about burn rates and velocities.

 

[Northridge]

I agree that the sine wave is not a smooth, simple pattern. In fact, I know it's not the case at all. The sine wave is rough and jagged due to several factors, but they can be summarized by saying that there are multiple frequencies traveling up and down the barrel at once, at something near 20,000fps in stainless steel. You can stumble upon a spike along the sine wave when tuning. With a tuner, it's characterized by a tiny group that goes to complete shat with a 1 mark move of the tuner. That said, there is still a dominant sine wave pattern that will give consistent and repeatable group shape on both sides of a sweet spot. That's what you're looking for!!

I see no difference in "forcing" a frequency with a tuner, as opposed to a smaller contour, or longer barrel, ie, less stiff barrel. I see tuners much like changing barrel stiffness without affecting velocity. They leave that up to the load...much like changing bbl length but keeping the same velocity, changing the frequency but not speed of the load. This is how tuners work, by optimizing where the muzzle is when the bullet reaches the muzzle....Timing.

The tuner being at the end of the bbl is adjusting the average of all the frequencies going on at once, behind it.

As to less stiff barrels offering a wider node...I agree. A tuner(mass) at the end of the barrel literally does create more muzzle deflection and a wider arc(amplitude) while the bullet is still in the barrel. That's an interesting statement on its own because physics teaches us that more mass at the muzzle will reduce amplitude. That's true, over time, but in the time we're concerned about, while the bullet is in the barrel, it's not the case at all...making a stiff barrel act like a less stiff barrel in terms of amplitude/muzzle deflection and its affect on tuning.

Interesting discussion, even if it was about burn rates and velocities.

I agree never gets old discussing what we find vs what is the theoretical conclusion, threads do evolve though not intended as our minds day dream over the possibility's as we share our ideas. I agree with your explanation as it makes complete sense to me.

Shawn Williams

 

[INTJ]

I am really agnostic on whether ES and/or SD is important. I started out tuning at short range for LR BR, and I did pretty well tuning that way but making sure my chosen loads had reasonably low ES. Early this year at Deek Creek, the load I found at 200 yds gave me some 5" 10-shot groups and a 2.9" 5-shot group at 1000 yds.

When I changed my LG barrel and finished my HG, I started initial tuning at 300 yds. With both rifles, the best 300 yd load wasn't the best at 1000. Now I was able to identify the node that shot best at 1000 at 300.

I then started tuning using the round robin ladders at 1000 yds and my groups have tightened. Like I mentioned earlier, I don't usually use a chrono when tuning at 1000, but when I have chronoed my best 1000 yd loads, the ES is always in the single digits to low teens. So I took it as a given that a good 1000 yd load would also have a good ES.

The biggest downside to my short range tuning is the amount of ammo takes. I think I need to see 5-shot groups and repeatability to be happy with a load, and that burns a lot of barrel life. The 1000 yd ladders show good load in MUCH fewer shots. Such to the point that I am not tuning at short range anymore, since the 1000 range is only 2.5 hours away and I am a member.

The long range hunters seem to swear by low ES. I developed a 338 Lapua load for a customer recently. He made a hit at 2600 yds (witnessed) with this load and also made an offhand hit at 1300. He said he the only thing he didn't like about the load was the ES--It was 22 FPS. (That was the ES for the best group I found.) To which I relied something like "Dude! If you are nailing all your long range targets, and even made a hit at 2600, the ES isn't an issue."

I found his load at 100 yds. I have in fact found several hunting rifle loads at 100 yds, all with reasonable ES, and then validated them out past 1000. So the idea that I could take a load with 50 FPS ES and do the same thing is interesting, since I have just taken it as a given that if I was developing loads at short range I needed to make sure the ES was low.

 

[NZ_Fclass]

I suggest that, given that there is no hard data.. we go our usual route and test each hypothesis i.e. we develop our loads, as per normal.
What we DO know, is that certain powders perform better with different primers, in the same case. Whether this refers to ignition time or ignition temperature, I have no idea.

 

[Alex Wheeler]

Do you not worry about ES -at all- Alex? Or just once it’s within reason you make sure that positive compensation on the load tune takes case of the rest?

Vertical is easy to think about as ES and positive compensation but you actually said “group size”, which isn’t just vertical either. Any thoughts on vertical vs horizontal?

No I don't worry about it at all. It will work itself out. If you do all the testing you should be doing you will end up with an accurate load and the es will be what it is. I have hunting rifles that group 3" at 1k in the 20s for es. Different primers will lower the es and make the group bigger. Every bench gun I have tuned will end up with es in the teens usually. Only a couple tenths away is single digits and bigger groups. I tune every thing at 1k and really have never seen best es and groups line up. So if they do not correlate why look at them? That said your not going to end up with crazy es if you tuned the rifle for accuracy. With good practices and good components and a well built rifle you just dont see crazy es to begin with.

 

[Alex Wheeler]

traditional full steel contours yes, carbon fiber is a different cat all together.. I also find light contours perform better often being spanked more from a charge weight prospective, obviously safe pressure being observed on the upper end.

Shawn Williams

Yes I find that too and its interesting. Most of the light sorters like to run just off of bolt lift. Drives me crazy.

 

[Alex Wheeler]

I agree that the sine wave is not a smooth, simple pattern. In fact, I know it's not the case at all. The sine wave is rough and jagged due to several factors, but they can be summarized by saying that there are multiple frequencies traveling up and down the barrel at once, at something near 20,000fps in stainless steel. You can stumble upon a spike along the sine wave when tuning. With a tuner, it's characterized by a tiny group that goes to complete shat with a 1 mark move of the tuner. That said, there is still a dominant sine wave pattern that will give consistent and repeatable group shape on both sides of a sweet spot. That's what you're looking for!!

I see no difference in "forcing" a frequency with a tuner, as opposed to a smaller contour, or longer barrel, ie, less stiff barrel. I see tuners much like changing barrel stiffness without affecting velocity. They leave that up to the load...much like changing bbl length but keeping the same velocity, changing the frequency but not speed of the load. This is how tuners work, by optimizing where the muzzle is when the bullet reaches the muzzle....Timing.

The tuner being at the end of the bbl is adjusting the average of all the frequencies going on at once, behind it.

As to less stiff barrels offering a wider node...I agree. A tuner(mass) at the end of the barrel literally does create more muzzle deflection and a wider arc(amplitude) while the bullet is still in the barrel. That's an interesting statement on its own because physics teaches us that more mass at the muzzle will reduce amplitude. That's true, over time, but in the time we're concerned about, while the bullet is in the barrel, it's not the case at all...making a stiff barrel act like a less stiff barrel in terms of amplitude/muzzle deflection and its affect on tuning.

Interesting discussion, even if it was about burn rates and velocities.

Mike, the part about a tuner increasing amplitude is interesting. Any of my experiance adding a mass to the muzzle has reduced amplitude at the target. Poi shifts less vertically across charges. Where a lighter contour barrel has a larger amplitude at the target, much more vertical poi shifts across charges. Any thoughts on that?