My HBN experience and process

[1mechanic]

Ok the way I understand is you have barrel length ( the quarter mile ), you have the weight of the bullet ( the weight of the car ) and then you have acceleration, the pressure behind the bullet ( the amount of pressure on the throttle pedal ). The less pressure you put behind the bullet especially the peak the slower it will go in the small amount of time for the barrel length. The more pressure ( the harder you push the pedal ) the more speed you'll get for the small amount of time.

Not the greatest analogy but reduce friction and you reduce pressure like reducing a load charge, ( like reducing traction and spinning tires instead of putting pressure to the track ).

 

[QuietTexan]

Pressure is the result of a constriction, not a measure of flow or energy. I get where you're going with the analogy, but it's flawed in that "pressure" in your example is really power output. Pushing the pedal harder increases available energy by burning more fuel, whereas a rifle case has a finite amount of fuel available.

Reducing pressure doesn't translate to reducing total energy output, it's a change in timing of energy being transferred.

The energy budget for a rifle cartridge firing is the total potential energy of the powder mass measured in joules (and little bit from the primer) reduced by losses to heat. Heat losses are from friction mainly, but there's also compressing the air in the barrel in front of the bullet (increasing it's temp as it's compressed, Charles's Law), sound and light discharge from the crown (both sound and light are forms heat transference), heat absorbed by the brass case, and even movement of the brass case and chamber itself takes energy out of the system. Chamber pressure is a result of constricting the flow of gas created by powder burning out of the case through the barrel, with the bullet acting as a part of the pressure vessel and relieving pressure by adding more volume to the system as it moves down the bore.

At a lower peak pressure the same amount of energy is still transferred, but over a longer time period. Since acceleration is a measure of the change in velocity (feet per second) over time (per second), increasing the length of the application of a force nets at worst an equal acceleration rate because time factors in exponentially (feet per second per second aka feet per second squared) and any reduction in velocity at a particular point in time get's reweighted by the exponent. The end velocity should be at worst the same because energy is the same, at best faster because of reduced heat loss to friction netting an increase in energy imparted to the bullet.

This squares with what Calvin is seeing in higher velocities with identical loads. Reduced friction results in lower energy loss. Pressure is lower because the bullet accelerates faster and reduces the constriction on gas expansion.

When I said we could potentially look at the integral of pressure curves, that was a backwards way of wondering if there is a direct enough relationship between pressure-over-time to energy in joules to make a comparison. That would confirm that energy content of the powder is the driving factor behind velocity, and that velocity gains from friction loss are minor comparatively. This would also square with Calvin in that he saw single low single digit increase in velocity from the HBN coating on the bullet and the bore. Variance in charge weight (as a proxy for mass of propellant) will have more effect than HBN coating - if ES x 5 is greater than the increase in velocity he saw, there would likley be a weak correlation between HBN and increased velocity since it happens inside the normal range of velocity variance due to charge weight variance.

 

[asd9055]

Pressure is the result of a constriction, not a measure of flow or energy. I get where you're going with the analogy, but it's flawed in that "pressure" in your example is really power output. Pushing the pedal harder increases available energy by burning more fuel, whereas a rifle case has a finite amount of fuel available.

Reducing pressure doesn't translate to reducing total energy output, it's a change in timing of energy being transferred.

The energy budget for a rifle cartridge firing is the total potential energy of the powder mass measured in joules (and little bit from the primer) reduced by losses to heat. Heat losses are from friction mainly, but there's also compressing the air in the barrel in front of the bullet (increasing it's temp as it's compressed, Charles's Law), sound and light discharge from the crown (both sound and light are forms heat transference), heat absorbed by the brass case, and even movement of the brass case and chamber itself takes energy out of the system. Chamber pressure is a result of constricting the flow of gas created by powder burning out of the case through the barrel, with the bullet acting as a part of the pressure vessel and relieving pressure by adding more volume to the system as it moves down the bore.

At a lower peak pressure the same amount of energy is still transferred, but over a longer time period. Since acceleration is a measure of the change in velocity (feet per second) over time (per second), increasing the length of the application of a force nets at worst an equal acceleration rate because time factors in exponentially (feet per second per second aka feet per second squared) and any reduction in velocity at a particular point in time get's reweighted by the exponent. The end velocity should be at worst the same because energy is the same, at best faster because of reduced heat loss to friction netting an increase in energy imparted to the bullet.

This squares with what Calvin is seeing in higher velocities with identical loads. Reduced friction results in lower energy loss. Pressure is lower because the bullet accelerates faster and reduces the constriction on gas expansion.

When I said we could potentially look at the integral of pressure curves, that was a backwards way of wondering if there is a direct enough relationship between pressure-over-time to energy in joules to make a comparison. That would confirm that energy content of the powder is the driving factor behind velocity, and that velocity gains from friction loss are minor comparatively. This would also square with Calvin in that he saw single low single digit increase in velocity from the HBN coating on the bullet and the bore. Variance in charge weight (as a proxy for mass of propellant) will have more effect than HBN coating - if ES x 5 is greater than the increase in velocity he saw, so there's a weak correlation between HBN and increased velocity since it happens inside the normal range of velocity variance due to charge weight variance.

I for one, I am impressed with the details
And explanation
We are really looking for the fine balance for friction.

 

[Pdvdh]

I get where you're going here and I agree with the general direction. But I'm not sure the last part is worded precisely enough to say I agree fully.

In this instance there would be a reduction in PEAK chamber pressure, but the result is a flattened curve and not a decrease in total amount of gas expansion if the mass of propellant is constant. Figuring the integral of each pressure curve might be a shortcut to confirm, but the total amount of work done by a fixed mass of propellant in the same sized pressure vessel should be the same even with a lower peak pressure. So yes PEAK pressure is reduced but that doesn't translate to loss of velocity.

Coat a bore and bullets with HBN and the MV drops, compared to the same exact load in the same rifle. Every time, in every rifle, I've applied HBN treatment. That's the universal experience.

Has Calvin stated he measures an increased MV after HBN treatment, with the identical load and powder charge? If so, that would be the first I've heard anyone experience that following HBN treatment.

My observation is; the size of the pressure vessel isn't static. It's dynamic as the bullet moves down the bore. I'm confident the integral of the area under the pressure curve will be reduced following HBN treatment.

The only possible explanation for reduced MV with reduced bore friction is the reduction of the integral of the area under the pressure curve. IMO, that reduction will be due to the dynamically changing size of the pressure vessel 'during the period of time' the bullet is within the bore.

Additionally, powder burn rate will undoubtedly be affected by the reduced peak pressures.

This may be the most comparable analogy:
Jam a bullet into the lands and peak pressures increase, causing increased MV. The additional bullet to bore friction caused by jamming the bullet into the lands alters the pressure curve.

Reduce the initial bullet to bore friction by jumping the bullet into the lands and peak pressure drops, as does MV.

Similarly, but not in the same exact manner, HBN reduces bullet to bore friction... >reducing pressure... >reducing MV...

 

[Calvin45]

Coat a bore and bullets with HBN and the MV drops, compared to the same exact load in the same rifle. Every time, in every rifle, I've applied HBN treatment. That's the universal experience.

Has Calvin stated he measures an increased MV after HBN treatment, with the identical load and powder charge? If so, that would be the first I've heard anyone experience that following HBN treatment.

My observation is; the size of the pressure vessel isn't static. It's dynamic as the bullet moves down the bore. I'm confident the integral of the area under the pressure curve will be reduced following HBN treatment.

The only possible explanation for reduced MV with reduced bore friction is the reduction of the integral of the area under the pressure curve. IMO, that reduction will be due to the dynamically changing size of the pressure vessel 'during the period of time' the bullet is within the bore.

Additionally, powder burn rate will undoubtedly be affected by the reduced peak pressures.

This may be the most comparable analogy:
Jam a bullet into the lands and peak pressures increase, causing increased MV. The additional bullet to bore friction caused by jamming the bullet into the lands alters the pressure curve.

Reduce the initial bullet to bore friction by jumping the bullet into the lands and peak pressure drops, as does MV.

Similarly, but not in the same exact manner, HBN reduces bullet to bore friction... >reducing pressure... >reducing MV...

No no, you're right, at equal charge weights the velocity DOES drop…I stated that I've been able, especially in more overbore rounds, to get higher velocity before seeing pressure signs BECAUSE y'all can go up in charge weight. Higher velocity sometimes, yes. At equal charge weights? Never.

 

[Pdvdh]

No no, you're right, at equal charge weights the velocity DOES drop…I stated that I've been able, especially in more overbore rounds, to get higher velocity before seeing pressure signs BECAUSE y'all can go up in charge weight. Higher velocity sometimes, yes. At equal charge weights? Never.

Exactly!

 

[Mikecr]

Unless it isn't about friction. With Moly, I believe it's about slight cooling of the charge as the moly vaporizes.
That HBN also affects MV is interesting.
I can swap between clean and WS2 coated, and see no MV change. This, while WS2 seems slippery as eel snot.

At any rate, I would not want MV change.
Everything I do in reloading is to prevent that, and I would not want to have to burn more powder either.
Really all I want is the best & most stable fouling.

 

[Calvin45]

Unless it isn't about friction. With Moly, I believe it's about slight cooling of the charge as the moly vaporizes.
That HBN also affects MV is interesting.
I can swap between clean and WS2 coated, and see no MV change. This, while WS2 seems slippery as eel snot.

At any rate, I would not want MV change.
Everything I do in reloading is to prevent that, and I would not want to have to burn more powder either.
Really all I want is the best & most stable fouling.

Eel snot! There's a visual!

And what you're saying makes good sense too if I understand it, that for you ws2 is primarily "stable fouling" so one more element to have a little more control over, and not so much a bullet lubricant in and of itself (slippery as it is).

I know I've heard guys using graphite in a similar capacity. No idea if it's a good idea.

 

[Slick8]

I'm going to try this in the near future.

Thanks for all the info, a new rabbit hole has been discovered.

 

[QuietTexan]

The only possible explanation for reduced MV with reduced bore friction is the reduction of the integral of the area under the pressure curve.

Lower muzzle velocity means less work is being done, so there has to be a reduction in force here. Pressure might be a part of that in burn efficiency (more below), but cannot be not the entirety of it. If the propellant mass (aka maximum potential energy) doesn't change yet total work decreases, there's an expensing of energy somewhere in the system and it's one that apparently doesn't correlate to pressure over time. Sounds like I'm wrong and the integral of the pressure curve isn't the right thing to look at trying to find a corollary for energy.

Additionally, powder burn rate will undoubtedly be affected by the reduced peak pressures.

That is true, and I stated I made the assumption that for high-pressure center fire cartridges that the change in burn velocity wouldn't be a factor inside the range of 40,000-65,000 PSI because the totality of burn doesn't change significantly. Since majority of burn happens in the first few inches of the barrel, and no barrel has been made that's long enough for friction to overcome the force of gas expansion and actually have the bullet slow down in the bore (look at that 308 Win test in the super long barrel) it seemed like a good assumption to remove one variable. Caveat - this would be in normal range of powder charges, I'm sure we've all stuck a pistol bullet with a light charge because energy budget was way, way too low and friction defiantly won.

I extrapolated that -sumption and it looks like it made an out me Back to the drawing board.

I think you're on to something with a potential root cause of reduced velocity being burn rate if some of the propellant is burning significantly later, or is not flowing thru the barrel fast enough (at least at the same rate as the bullet at any given point) to impart additional force on the bullet, increasing energy lost in the ejecta mass of gas. I'm going to go look at the back end of pressure curves more closely to see if maybe there is a significant loss of energy there. might show up as an excessively long pressure tail. It would make sense that an external loss of energy from the system in the largest component of all this (powder charge) would explain the decrease in muzzle velocity better than anything else.

Reduce the initial bullet to bore friction by jumping the bullet into the lands and peak pressure drops, as does MV.

HBN reduces bullet to bore friction... >reducing pressure... >reducing MV...

I do think still that's a bit of a stretch to put friction in here in relation to pressure. You brough up reduction in peak pressure as by-product of something else, likely burn efficiency or velocity (from above) and I'm agreeing with you there. I'll admit I made a poor assumption on the effect of burn timing.

But I'm still holding to I don't think there's a significant enough change in heat absorbed by the barrel or in heat generated by friction to explain an actual decrease in velocity, basically that the impact of reduced friction would have to be incredibly significant to meaningfully impact burn rate. I'll try to prove myself wrong though and model it in QL though. I'm thinking set very short barrel length with large enough charge to not fully burn (<75% maybe to start) and drastically change barrel friction input. I expect QL to dump out a higher velocity if I only reducing friction, and that I'll need to force an outsized impact of burn to see a decrease. But I'll check it out, let me see what I can do.

 

[Tech4]

No snake oil required, in fact your supposed to remove all oil.

Does it work the snake oil removed? I do wonder the mix of gunpowder and HBN what would be in the toxic cloud explicitly when using a brake.

 

[QuietTexan]

Unless it isn't about friction.

I think you're correct. I don't see MV changes with MS2. Barrel friction sems to be a minor part of the puzzle.

Similarly, but not in the same exact manner, HBN reduces bullet to bore friction... >reducing pressure... >reducing MV...

But for fun lets go the other direction. If reduced friction reduces muzzle velocity, increased friction should increase MV. The direct relationship has to work both ways.

Seems like copper fouling would also make this large of an impact on velocity if friction was the root cause. Copper fouling can sometimes cause high pressure issues in my experience, but I've never quantified a change in muzzle velocity due to it. Let's go with the assumption is it results in higher velocity since higher pressure (at least it shows higher pressure signs on the case), because that the assumption we're working with on the lower friction side.

My thought has always been fouling acts as a bore restriction since the metal buildup sits proud on the lands. Copper fouling is primarily at the muzzle end of the barrel, an any increase in velocity is at the end of the burn curve either way, increased friction or constriction.

So I went to look at static coefficient of friction for Copper-Copper and Copper-Steel.

Static coefficient:
Copper-Copper 1.6
Copper-Mild Steel 0.53
Aluminum-Aluminum 1.035
Cast Iron - Cast iron 1.1

Dynamic coefficient:
Copper-Copper ??? (see below)
Copper-Steel is 0.36.
Aluminum-Aluminum 1.4
Cast Iron - Cast iron 0.15

I put in the AL and cast iron to show two metals with similar static coefficients can be drastically different dynamically, so there's no way to guess at which way copper would go.

I found one paper saying that dynamic coefficient for Copper-Copper ranged from 0.4 to 1.1, but wasn't able to control for removing oil from the surface of the material consistently. If it's on the low end of 0.4 not a big deal, but if the 1.1 is correct then copper fouling might increase chamber pressure due to both increased friction and constriction.

Probably too many variables in alloy metals and hardness to really make a correlation though. Interesting thought experiment but I'm not going to go deeper. +1 to Pdvdh's theory because it didn't fail this test outright though.

No no, you're right, at equal charge weights the velocity DOES drop…I stated that I've been able, especially in more overbore rounds, to get higher velocity before seeing pressure signs BECAUSE y'all can go up in charge weight. Higher velocity sometimes, yes. At equal charge weights? Never.

I'll admit I misread that.

 

[Pdvdh]

What evidence is there to support the hypothetical suggestions that modified bullet to bore friction isn't the causative factor reducing MV with HBN treated bullets/bores?

Only one item is being changed in the mix. HBN is applied to the bullet/bore surface. MV is reduced.

By all accounts, HBN is inert. HBN isn't oxidized at the temps experienced during powder combustion? Should have no affect on powder combustion.

Is there a competing hypothesis with an equally logical explanation? Any corroborating empirical evidence?

Pixie dust? Black magic? Voodoo?

Whoops...

 

[1mechanic]

I think everyone is hung up on friction and it making heat or reducing it depending on the coefficient.

What if we look at it like drag? No coating, lots of drag holding bullet from going down the barrel creating pressure.

Low drag, bullet goes down the barrel easier not making as much pressure and pressure is what makes more fps. Hence why adding more powder creates more pressure and more fps.