confused about pressure meanings

[Cliff6]

I'm looking at Hodgdon's load data for 148 grain 38 special DEWC loads. I'm trying to find a softer shooting load.
Looking at just the lightest loads:
WST ---- at 2.5 gr shows 680 f/s and 13,000 PSI
Titegroup - at 2.7 gr shows 771 f/s and 7,700 CUP
W231 ------ at 3.5 gr shows 869 f/s and 14,200 CUP

I'm really confused. I know CUP and PSI are different, but I don't understand it.
I would think that the Titegroup load would shoot the softest, however, WST is over 100 f/s slower!

Can someone help explain this to me?

 

[fxvr5]

Different powders = different burn rates = different 'required' charge weights for a given speed.

Ignore pressure for your current task. Focus on velocity.

 

[fxvr5]

PSI and CUP do not measure pressure the same way so their values will not be equal. Ever. Except by chance. They're not really a guide to anything useful in most cases except to tell you when pressure is high and you don't want to exceed the maximum SAAMI value - for safety reasons.

Other than that, what is your question?

 

[Cliff6]

PSI and CUP do not measure pressure the same way so their values will not be equal. Ever. Except by chance. They're not really a guide to anything useful in most cases except to tell you when pressure is high and you don't want to exceed the maximum SAAMI value - for safety reasons.

Other than that, what is your question?

Ok, so if I ignore the different pressures (all WELL below SAAMI maximums) would it be reasonable to think that the slowest velocity load would have the lowest recoil?

 

[fxvr5]

Ok, so if I ignore the different pressures (all WELL below SAAMI maximums) would it be reasonable to think that the slowest velocity load would have the lowest recoil?

Yes. Recoil force has 4 components. 1) Bullet weight. 2) Bullet velocity. 3) Gun weight. 4) Gunpowder weight.

In this instance, bullet weight is the same, gun weight is the same, and gunpowder weight is close enough to the same that it has little effect on the calculation. Thus, the big factor is bullet speed, and a lower bullet speed means lower recoil.

You can plug those numbers into a calculator to calculate the recoil force;
http://kwk.us/recoil.html

Chamber pressure, by itself, does not predict recoil force. Gas pressure at the muzzle does contribute to recoil force (via gunpowder weight and gas velocity) and it is usually 'estimated' with a constant that varies depending on the firearm type. There is an explanation of that at the link, though it can be a little confusing. And for the most part can be ignored.

 

[243winxb]

slowest velocity load would have the lowest recoil?

I have no idea.

Should produce the lower muzzle energy? Speed + weight?

My guess is- The faster burn rate powder will reach peak pressure sooner, allowing pressures to drop sooner. More like a a hard quick shove?

But then again, a slow powder would maintain pressure longer, and peak later, may be more a lighter push?

Accuracy is my first consideration.

 

[Cliff6]

Yes. Recoil force has 4 components. 1) Bullet weight. 2) Bullet velocity. 3) Gun weight. 4) Gunpowder weight.

In this instance, bullet weight is the same, gun weight is the same, and gunpowder weight is close enough to the same that it has little effect on the calculation. Thus, the big factor is bullet speed, and a lower bullet speed means lower recoil.

You can plug those numbers into a calculator to calculate the recoil force;
http://kwk.us/recoil.html

Chamber pressure, by itself, does not predict recoil force. Gas pressure at the muzzle does contribute to recoil force (via gunpowder weight and gas velocity) and it is usually 'estimated' with a constant that varies depending on the firearm type. There is an explanation of that at the link, though it can be a little confusing. And for the most part can be ignored.

All that makes sense.

 

[fxvr5]

Recoil is just Newtonian physics. For every action there is an opposite and equal reaction. That's why it can be calculated so easily. The gunpowder weight is part of it because it is part of the 'ejecta' (the gunpowder weight part), which means it also comes out the end of the barrel but in the form of gas (the gas velocity part).

For people who want to torture themselves with math, Wikipedia has a page with formulas. https://en.wikipedia.org/wiki/Recoil

 

[rfwobbly]

Recoil is just Newtonian physics. For every action there is an opposite and equal reaction.

...and we've known this since 1680. Back when Walkalong started reloading.

 

[BBarn]

For those same bullet loads, the lowest velocity load produces the lowest bullet energy and bullet momentum. And in most cases, the perceived recoil will be the one with the lowest velocity/energy/momentum.

However, muzzle blast often increases the perceived recoil. So a load with larger amounts of slow burning powder might seem to have more recoil than another load with less powder and similar velocities.

With semi-autos, slide velocity can also affect perceived recoil. Slide velocity is mostly a function of muzzle velocity, but the faster pressure rise of faster burning powders might lead to a slightly higher slide velocity (for a given bullet velocity), along with a corresponding effect on perceived recoil.

With all three of the OP revolver loads using powders of similar burn rate, I would expect the perceived recoil to correlate fairly well to bullet velocity.

Probably an unnecessarily long-winded answer.

 

[jmr40]

Recoil is determined by:

Weight of the projectile
Weight of the powder charge
Velocity of the projectile
Weight of the firearm

You can plug the numbers into a recoil calculator

ShootersCalculator.com | Recoil Calculator

There isn't going to be a huge difference in any of those loads, but assuming equal bullet weight and equal firearm weight the load with the slowest velocity and least powder will recoil less.

 

[fxvr5]

However, muzzle blast often increases the perceived recoil. So a load with larger amounts of slow burning powder might seem to have more recoil than another load with less powder and similar velocities.

For two powders that produce the same speed with the same bullet, the powder that uses more charge weight will produce more recoil. That's the 'conservation of mass' thing at the Wikipedia link. It's real, and measurable even with a simple tool like a Ransom Rest which demonstrates it as muzzle rise. But with the small difference with the fast powders in the OP's post mean it will barely be perceptible.
https://www.shootingtimes.com/editorial/measure-relative-handgun-recoil/99442

 

[25-20 WCF]

PSI and CUP do not measure pressure the same way so their values will not be equal. Ever. Except by chance….

The two measurement systems can produce identical values, not often but not “never”. See below from the 1990 Hercules manual, refer to the .30 Carbine and .45-70 data in particular. “Never” is a dangerous concept to use….



BTW pressures do matter, the powder is ejecta and the higher the pressure the higher the gas velocity at exit. This is additive to the bullet energy/momentum, the heavier the powder weight and velocity the heavier the recoil will be. Equal bullet velocities with different gas mass/velocities/energies/momentums will effect the perceived recoil. Pressure does matter…


.

 

[George P]

Ok, so if I ignore the different pressures (all WELL below SAAMI maximums) would it be reasonable to think that the slowest velocity load would have the lowest recoil?

Slowest velocity with the lightest bullet weight in the heaviest gun gives the lowest recoil - that is Newton

 

[Jim Watson]

A bit of pressure can improve powder burnup and give more uniform ballistics.
That poofty load of titegroup will be erratic. Not that it matters much at across-the-poker-table ranges.

 

[fxvr5]

The two measurement systems can produce identical values, not often but not “never”. See below from the 1990 Hercules manual, refer to the .30 Carbine and .45-70 data in particular. “Never” is a dangerous concept to use….

And you've proved my point. A rare event indeed, to the point where by probability it seems like chance.

BTW pressures do matter, the powder is ejecta and the higher the pressure the higher the gas velocity at exit. This is additive to the bullet energy/momentum, the heavier the powder weight and velocity the heavier the recoil will be. Equal bullet velocities with different gas mass/velocities/energies/momentums will effect the perceived recoil. Pressure does matter…

To expand this, when comparing two powders, a slower powder can produce less peak chamber pressure, yet more velocity and higher gas pressure at the muzzle.
https://www.shootingtimes.com/editorial/compensators-pressure-gas/99170