Pressure question

[Mint]

I'm in the process of reading/learning, so this will be a very basic question about the relationship of pressure to recoil/velocity.

These 2 loads from Hodgdan. Why is pressure higher for a load with less recoil, and less velocity?

https://i.imgur.com/Lympotz.png

[Winger Ed.]

The burning rate/speed has something to do with it.

A fast powder will burn and hit you like a hammer blow. They do best in short barrels.
Slower powders will be more like a push, as their pressure comes on and really shine in longer barrels.

A decent demonstration is what I found out with .45-70s out of a Marlin CB.
A smokeless load kicks like a mule compared to the 'mushy' recoil of the same 405 gr boolit
going the same speed but with a full charge of double 'FF' black powder.
As I recall, the speed was right at 1350 fps.

[JonB_in_Glencoe]

Check into the pressure curve for each of those powders.

[gwpercle]

I'm in the process of reading/learning, so this will be a very basic question about the relationship of pressure to recoil/velocity.

These 2 loads from Hodgdan. Why is pressure higher for a load with less recoil, and less velocity?

https://i.imgur.com/Lympotz.png

I can't tell you why the pressure is higher ... I'm not a MIT Graduate ...
but I can tell you why load #2 develops more recoil 3.76 foot pounds ... it is the weight of the powder charge 15 grains H110 ... 5.4 grs Titegroup develops only 1.27 foot pounds recoil .
I can't explain that either but I know it is true ... the lighter the powder charge ... the less recoil ... I have a very simple mind and discovered this ballistics stuff can be extremely complicated . I just accept certain things as true and don't try and discover why ...
It tends to overload what little sane mind I have left .
Gary

[MT Gianni]

A powder may generate peak pressure in the first 0.032" of it's burn. A second powder might be much slower peaking in the first 1.123" of burn. The first powder may generate 1.0 cubic feet of gas. The second powder may generate 1.7 cu ft of gas.
Pressure is resistance to flow. If there is 1 cu ft of gas released in 0.003 of one second in a 4 bore shotgun it will have less pressure than if it were released in a 0.224 bore. It tries to flow to an equal pressure with atmospheric and does so by pushing against all that resists it. In whats relevant to us, that is a lead slug moving out of a bll, and expanding the space in which the gas was compressed. This increases the space, reduces the pressure of the gasses and all occurs in a millisecond.

Pressures are not all equal because the time they exert on the surfaces is not equal. Peak pressure is still peak pressure.

The solution is to read a lot of manuals, seeing that some loads have a higher pressure and less velocity with one bullet weight and caliber and it may be the opposite in the next bore size.

Many thing effect recoil including bullet weight, firearm weight and velocity. It is complicated enough that one should not look for simple solutions but try to grasp a general understanding.

[Hick]

Pretty much covered above but I can tell you that Titegroup is in fact a much faster burning powder than H110. It reaches its peak pressure pretty much before the bullet can move much. H110 has a slower pressure rise and the bullet can get moving sooner, which makes more space in the case so the peak pressure is lower.

[Mint]

Pretty much covered above but I can tell you that Titegroup is in fact a much faster burning powder than H110. It reaches its peak pressure pretty much before the bullet can move much. H110 has a slower pressure rise and the bullet can get moving sooner, which makes more space in the case so the peak pressure is lower.

Ah! Thank you!! Very good observation. You made me jump off the toilet early cause I had to go check my spreadsheet. I had the color formatting going in the wrong direction

And thanks to the other replies. I love formulas so I do enjoy this stuff.

[Mk42gunner]

You made me jump off the toilet early cause I had to go check my spreadsheet. I had the color formatting going in the wrong direction

And that is a mental image I did not need, at all.

I think you will fit in nicely around here, welcome aboard.

Robert

[Mint]

And that is a mental image I did not need, at all.

I think you will fit in nicely around here, welcome aboard.

Robert


:guntootsmiley::guntootsmiley:

[dverna]

Look at the formula for recoil. There is no component of pressure. It is not complicated at all.

Years ago there was a double blind test of slow vs fast powders done by Neil Winston with 12 ga loads. He proved a person could not tell any difference in recoil.

There is a lot of misinformation on the subject. But facts do not matter. It is what you believe that matters.

That is why placebos “work”.

If you want a softer shooting load, reduce the weight of the bullet and/or reduce the velocity. Dinking around with powders will be fun, expensive and a waste of time. Physics does not change.

[JimB..]

When you fire a round loaded with Titegroup the pressure peaks very quickly because all powder is consumed very quickly. Assume this happens in the first 2” of barrel, so you’ve got 33kpsi behind the bullet, it goes another 3” and the volume of space behind the bullet has doubled (assume 1” of case) and the pressure falls in half. About this point the friction between the bullet and the barrel is greater than the force of pressure on the bullet, so the bullet is slowing down.

Conversely H110 burns slowly, so pressure builds over a longer period (vs TG’s spike). Perhaps it reaches peak pressure at 10” of barrel and it’s still burning, when the bullet exits a 16” barrel pressure is down just a little, the bullet has been accelerating for most or all of the barrel length.

BTW, I’m making up the numbers above, really don’t want to go look up the details for each powder and do the math.

Recoil is more about perception than reality. The bullet is moving forward, so the gun moves backwards. Lots of forces at play from the mechanics of the action to the friction of the barrel to the mass of the powder charge. On top of that, the speed of the powder, the mass of the gun, and how you grip the gun affect how it feels, which is what you care most about. Easy to go down this rabbit hole, but maybe ignore it for now and consider it some years in the future.

[Mint]

When you fire a round loaded with Titegroup the pressure peaks very quickly because all powder is consumed very quickly. Assume this happens in the first 2” of barrel, so you’ve got 33kpsi behind the bullet, it goes another 3” and the volume of space behind the bullet has doubled (assume 1” of case) and the pressure falls in half. About this point the friction between the bullet and the barrel is greater than the force of pressure on the bullet, so the bullet is slowing down.

Conversely H110 burns slowly, so pressure builds over a longer period (vs TG’s spike). Perhaps it reaches peak pressure at 10” of barrel and it’s still burning, when the bullet exits a 16” barrel pressure is down just a little, the bullet has been accelerating for most or all of the barrel length.

BTW, I’m making up the numbers above, really don’t want to go look up the details for each powder and do the math.

Recoil is more about perception than reality. The bullet is moving forward, so the gun moves backwards. Lots of forces at play from the mechanics of the action to the friction of the barrel to the mass of the powder charge. On top of that, the speed of the powder, the mass of the gun, and how you grip the gun affect how it feels, which is what you care most about. Easy to go down this rabbit hole, but maybe ignore it for now and consider it some years in the future.

Makes perfect sense, thank you. I suppose I didn't know the pressure number was "peak," as now that would make more sense.

I do wonder however if AVERAGE pressure is still greater in a slower burning powder usually?

[BLAHUT]

Look at the formula for recoil. There is no component of pressure. It is not complicated at all.

Years ago there was a double blind test of slow vs fast powders done by Neil Winston with 12 ga loads. He proved a person could not tell any difference in recoil.

There is a lot of misinformation on the subject. But facts do not matter. It is what you believe that matters.

That is why placebos “work”.

If you want a softer shooting load, reduce the weight of the bullet and/or reduce the velocity. Dinking around with powders will be fun, expensive and a waste of time. Physics does not change.

I am not a betting man, but I will wager, if I give you two cartages for my 45/70, one loaded with 27 grs of 5744 and the other one loaded with 42 grs of blackhorn209, same bullet, same everything except powder, and You fire then back to back, You will be able to tell and know the difference.

[M-Tecs]

I am not a betting man, but I will wager, if I give you two cartages for my 45/70, one loaded with 27 grs of 5744 and the other one loaded with 42 grs of blackhorn209, same bullet, same everything except powder, and You fire then back to back, You will be able to tell and know the difference.

Very true. While pressure is normally not part of the equation the weight of what is ejected from the muzzle is. In addition to the bullet weight that also includes the weight of the powder.

[JimB..]

Makes perfect sense, thank you. I suppose I didn't know the pressure number was "peak," as now that would make more sense.

I do wonder however if AVERAGE pressure is still greater in a slower burning powder usually?

Peak is for safety, it only takes a small fraction of a second for a gun to come apart. Long slow push will give a higher average, and velocity, but it works best when you have enough barrel.

[Mint]

Peak is for safety, it only takes a small fraction of a second for a gun to come apart. Long slow push will give a higher average, and velocity, but it works best when you have enough barrel.

Thank you swanky boolit master