Felt Recoil: High vs Low Pressure

[samb300]

I don't have QuickLoad, so this is more of a theoretical question unless someone can chime in with a quick analysis to help me out.

What effect does a "high" versus a "low" pressure cartridge have on felt recoil? If I run the numbers on JBM it clearly shows the more powder you add to achieve the same velocity, the greater the recoil. However, this doesn't take into account the case volume, powder burn rate, or pressure.

Take for example, a 6 Dasher shooting a 105 Hybrid at 2950 fps with 32.0gr Varget. That will obviously be high pressure, but is burning a very small amount of fast burning powder to achieve a good velocity. How will that compare to something like a 6x47L (or 6XC or 6 Creedmoor) that uses 38.0gr of H4350 to achieve the same speed?

I recognize these numbers are somewhat theoretical, but they're in line with known loads.

Thanks,

Sam

 

[spife7980]

JBM - Calculations - Recoil

www.jbmballistics.com

 

[samb300]

JBM - Calculations - Recoil

www.jbmballistics.com

The third sentence of my post describes me already running the recoil numbers on JBM.

 

[XLR308]

It doesn't matter pressure wise it's pure physics, x weight rifle firing Y weight bullet at z velocity equals recoil energy and speed.

 

[Supersubes]

I’m not sure JBM can calculate what’s going on. Recoil just doesn’t rise in a linear fashion, especially at the upper end of pressure where all the sudden recoil begins to spike. Just my observation.

 

[samb300]

It doesn't matter pressure wise it's pure physics, x weight rifle firing Y weight bullet at z velocity equals recoil energy and speed.

I understand basic physics, but even your statement is over-simplified since the JBM calculator shows that increasing the powder charge weight increases recoil even as bullet weight, velocity, and rifle weight are constant.

 

[XLR308]

I understand basic physics, but even your statement is over-simplified since the JBM calculator shows that increasing the powder charge weight increases recoil even as bullet weight, velocity, and rifle weight are constant.

I have allways considered pressure in the equation to be neutral since it is exerted in all directions but I'm not a physicist or rocket scientist so may have something to learn as usual.
I think the reason it shows an increase even though all else is the same is it relies on accurate input on your part and is being manipulated.
An increase in pressure should also indicate an increase in velocity unless something is yielding from an excess of pressure.
Does that sound right ?

 

[mick243]

I understand basic physics, but even your statement is over-simplified since the JBM calculator shows that increasing the powder charge weight increases recoil even as bullet weight, velocity, and rifle weight are constant.

Don’t forget, the mass of propellant exits the muzzle at great velocity, therefore more propellant leads to more recoil (unless you have a brake, but that only modifies the recoil pulse after projectile exit so the mass of propellant still add to the initial slope of the recoil pulse)

 

[mcfred]

What effect does a "high" versus a "low" pressure cartridge have on felt recoil? If I run the numbers on JBM it clearly shows the more powder you add to achieve the same velocity, the greater the recoil. However, this doesn't take into account the case volume, powder burn rate, or pressure.

Generally, chamber pressure/burn rate doesn't really matter. The charge weight and velocity do. All else being equal, 50 grains of gas at 3000fps (at exit) will produce more recoil than 40gr of gas at 3000fps.

Of course it's more complicated than that, but it's a convenient 90% solution.

Add a muzzle device and those calculated numbers are virtually meaningless.

 

[Steel head]

I can definitely feel a difference with my 260 shooting 140’s at 2700 vs 2800+.
It’s not huge but it’s there.

 

[Western Living]

Pressure is not a constant, but instead we are typically concerned with peak pressure to ensure safety. Those peak pressure events almost always happen before the bullet exits the muzzle, usually in the first inch of bullet travel. Quickload will show the muzzle pressure, or the pressure at the time the bullet base exits the muzzle. This is almost always low. In handguns its low because peak pressures are rarely very high. In rifles it is low because the combustion finishes are the pressure is relieved to a great degree as the bullet travels down the long barrel.

Powder mass does contribute more to recoil than an equal portion of bullet mass because it is accelerated to a higher velocity than the bullet. Not all powder is accelerated to the same velocity, so a constant can only be used to estimate the average velocity of the powder gases. One such constant for estimation is 1.8 times the bullet's muzzle velocity.

High pressure does appear to be correlated with fierce sound pressure. Although we cannot ignore the contribution of muzzle breaks, porting, compensators or short barrels that direct more of the sound waves at the shooter's position, cartridges like .327 Federal Magnum have high muzzle pressures from short barrels, whereas .45ACP has a relatively low muzzle pressure from a similarly short barrel. The sound of the .327 is much more deafening. Even if we account for the supersonic shock wave by comparing it to a 90 grain .38 Special, the cartridge with the higher muzzle pressure is much louder. The sound pressure doesn't contribute to recoil in the proper sense, but it does have a great effect on "felt recoil" for many shooters.

 

[High H2o]

Of course it's more complicated than that, but it's a convenient 90% solution.

Damn, didn't know there was a term for what I've been doing my whole life

 

[Clark]

Recoil pain is invariant with chamber peak pressure.
The threshold of pain, I measure at ~ 20 psi skin pressure on the shoulder.


1) The most important thing in reducing pain is increasing area of the butt.
A 200 pound woman walking on you bare foot is much more comfortable than a 100 pound woman in high heels.
The high pressure per square inch caused by high heels caused Boeing to redesign their galley floors.

2) The second most important thing is recoil pad compliance.
If it is as soft as a woman's falsie, it will just compress to easily.
If it is hard as your truck tires, it will not compress.

3) The third most important thing is recoil pad thickness.
If it is too thin, there is not enough distance for deceleration.


In conclusion, we want to spread the recoil impulse over time and area to stay under 20 psi at the shoulder.
The best recoil pads I have found is the 1" thick Limbsaver grind to fit, but left unground for more area.

My 338WM with Limbsaver I can shoot all day, but my 30-30 with a small hard butt causes me pain.

 

[lte82]

The two main components of felt recoil are peak force and total momentum. Imagine peak force being the top of the force (or pressure) vs time curve, total momentum is the area under that curve. Higher pressure increases felt recoil by increasing the peak, which IMO is the biggest component of what you feel, and what pushes you off target. A slower burning powder with less pressure will give a wider curve but less peak, which gives more of that “push” feel.

A 6.5 creedmoor using varget @ 2750 FPS will have a much sharper recoil impulse and higher peak force than RL16 @ 2750, though the total momentum will be relatively the same. I usually find the lower peak force (lower peak pressure as well) easier to deal with on barricades, which is probably why most guys seem to be opting for lower velocity / lower pressure loads in PRS these days.