Determining "Recoil Efficiency"

[solarshooter]

I have shown some calcs in the past where I've done point assessments of certain cartridges/bullets/rifles to try and determine what is the lowest recoil way to get a certain wind number. Today I decided to elaborate on this a bit and assess recoil and wind number as a function of MV and caliber.

First, I created a reference bullet for each caliber which has a weight and BC representative of the highest performing bullets in that caliber.


I then estimated powder charges needed to get that bullet to the given MV in a roughly 20" barrel. This is cartridge agnostic, and may not be perfect. I use this in conjunction with bullet momentum to calculate total recoil.


I then calculate recoil in a 9lb rifle, run the bullet at the given speed to determine the wind number, and finally calculate wind# per recoil.


The way I would use this chart is to narrow in on what bullet at what speed gives you your desired performance and what the "recoil efficiency" of that combination would be. You could then pick your barrel length and cartridge to get you that performance target. For instance, if you ask what is the minimum recoil way to get an 8mph wind number gun, the answer is a 6mm bullet at 3200fps or so, aka a 6UM. It also shows you the recoil INefficiency of larger calibers - moving up in weight is almost always less recoil efficient than going faster.

 

[khuber84]

Those 325-335g7 257 cal bullets traveling 2800-2950 fps sure do have a sweet spot!

 

[Gstew1930]

This is good stuff

 

[KyleR1985]

For the ballistically challenged, a wind number is:

Bullet X moving at Y speed gives you ______________ performance in Z mph wind.

Can you fill in the blank, or correct the back of class guy?

 

[wind gypsy]

For the ballistically challenged, a wind number is:

Bullet X moving at Y speed gives you ______________ performance in Z mph wind.

Can you fill in the blank, or correct the back of class guy?

Its the wind speed at which a wind hold correlates 0.1 mil per 100 yards.

EX: 5 MPH gun or 5 MPH wind # with a 90 degree 5 MPH wind would have the following wind holds

300 yds - 0.3 mil
400 yds - 0.4 mil
500 yds - 0.5 mil
600 yds - 0.6 mil

Doesn't typically go to infinity but is a good quick way to figure wind corrections at reasonable distances.

 

[KyleR1985]

Its the wind speed at which a wind hold correlates 0.1 mil per 100 yards.

EX: 5 MPH gun or 5 MPH wind # with a 90 degree 5 MPH wind would have the following wind holds

300 yds - 0.3 mil
400 yds - 0.4 mil
500 yds - 0.5 mil
600 yds - 0.6 mil

Doesn't typically go to infinity but is a good quick way to figure wind corrections at reasonable distances.

Awesome thanks.

 

[Stinky Coyote]

excellent, what about another look (and it maybe it overlays this efficiency?) of 'most bc per gr of bullet weight' efficiency, and what diameter that generally lands on?

we might be able to finally find the end of this lrh road to the perfect most efficient choice lol (of what is most efficient blend of copper/lead bullets currently available, maybe it will help drive future development paths?)

 

[solarshooter]

excellent, what about another look (and it maybe it overlays this efficiency?) of 'most bc per gr of bullet weight' efficiency, and what diameter that generally lands on?

we might be able to finally find the end of this lrh road to the perfect most efficient choice lol (of what is most efficient blend of copper/lead bullets currently available, maybe it will help drive future development paths?)

The parameter you're looking for is called Form Factor.

Ballistic Coefficient is a measure of how resistant a projectile is to aerodynamic drag. The formula is:

g7 BC = SD/i7

SD = Sectional Density, mass of bullet/frontal area
i7 = Form Factor (g7), ratio of projectile measured drag coefficient/g7 reference projectile drag coefficient. Lower is better. Picking the correct reference is a whole different discussion, suffice it to say we should all be using g7 for the bullets we are interested in.

So there are two components to it. Heavier bullets with the same caliber get an increase in BC. However, you pay for it with lower MV/higher recoil for same MV. Form Factor is a measure of how aerodynamically efficient the shape is. This is "free" performance from a recoil perspective - a higher form factor bullet will give you a better trajectory for no additional recoil. If a lighter bullet has a higher form factor but lower BC than a heavier bullet, you might be able to drive it fast enough to make up the difference in BC and get a better trajectory for the same recoil.

I've compiled a list of top performing (both external and terminal ballistics) bullets from 22cal to 7mm. This is using BC values from AB app. Here it is sorted by i7:

 

[AZ_Hunter]

The market really needs a factory 25PRC/SAUM/Westerner with the 130+ gr bullets. That really does look like the sweet spot.

 

[solarshooter]

A 25cal at 3k is high on my list of next cartridges. I have a standard bolt face and I love the 284 case, so I'm eyeing a 25-284, or maybe a 25-284 Shehane to get 3k in a 20" tube. It has similar recoil to a 6UM but better barrel life. Kind of a goofy "special snowflake" wildcat but I'm a reloader so why not.

 

[willfrye027]

Love my 25 creedmoor with 130 class at 2800-2900.

However I have been unable to shoot the difference at 600-1000 yards between it, a 6mm creedmoor with 109s, and 22 creedmoor with 88s. There is a noticable (to me) recoil difference stepping down from 25cal to 6mm with exactly the same gun weight and nearly the same powder charge. The 22 creedmoor is 10oz lighter and feels a little different..current preference is a 9.5lb 6mm creedmoor.

 

[solarshooter]

How long is the barrel on that 25CM?

I have a 9.75lb suppressed 6CM that is an absolute joy to shoot. If I could hunt with 22cal in my state I would build a 22CM in a heartbeat.

 

[B_Reynolds_AK]

The 22 creedmoor is 10oz lighter and feels a little different..current preference is a 9.5lb 6mm creedmoor.

What do ya mean in regards to the 22 CM?

 

[Stinky Coyote]

The parameter you're looking for is called Form Factor.

Ballistic Coefficient is a measure of how resistant a projectile is to aerodynamic drag. The formula is:

g7 BC = SD/i7

SD = Sectional Density, mass of bullet/frontal area
i7 = Form Factor (g7), ratio of projectile measured drag coefficient/g7 reference projectile drag coefficient. Lower is better. Picking the correct reference is a whole different discussion, suffice it to say we should all be using g7 for the bullets we are interested in.

So there are two components to it. Heavier bullets with the same caliber get an increase in BC. However, you pay for it with lower MV/higher recoil for same MV. Form Factor is a measure of how aerodynamically efficient the shape is. This is "free" performance from a recoil perspective - a higher form factor bullet will give you a better trajectory for no additional recoil. If a lighter bullet has a higher form factor but lower BC than a heavier bullet, you might be able to drive it fast enough to make up the difference in BC and get a better trajectory for the same recoil.

I've compiled a list of top performing (both external and terminal ballistics) bullets from 22cal to 7mm. This is using BC values from AB app. Here it is sorted by i7:
View attachment 823090
View attachment 823091

thanks, I figured you'd have done more stuff like this, am I reading it right the darkest green is the winners and tends to put out the most bc for the diameter at those weights? or has that alone been broken out without the recoil factors applied? just thinking about lead and copper bullets down the tubes we throw them down if there's a diameter that seems to spit out the most bc per grain of weight overall?

I thought I got nerdy with excel and studying, I was reading old ballistics tables books long before the computers came along when I was 12, prolly explains why excel is the main tool I use now for work. Data mine and make better tools and uses of the data. Anyhow, pretty cool work you're doing.

 

[willfrye027]

What do ya mean in regards to the 22 CM?

I think it’s recoil velocity, or possibly less barrel weight and more muzzle jump. The recoil from the 22cm just feels snappier even though it’s about the same or maybe less physical push as the 6cm.

Both are tikkas in rokstock with maven rs 1.2. The 6cm is a 26” taperless 750 contour, the 22 creedmoor is a tikka contoured 24” barrel.

 

[B_Reynolds_AK]

I think it’s recoil velocity, or possibly less barrel weight and more muzzle jump. The recoil from the 22cm just feels snappier even though it’s about the same or maybe less physical push as the 6cm.

Both are tikkas in rokstock with maven rs 1.2. The 6cm is a 26” taperless 750 contour, the 22 creedmoor is a tikka contoured 24” barrel.

Oh interesting. I havn't received my 22 CM yet, but sure love the recoil of the 6 CM. I suppose not being able to use a suppressor doesn't help at all in your case.

 

[solarshooter]

thanks, I figured you'd have done more stuff like this, am I reading it right the darkest green is the winners and tends to put out the most bc for the diameter at those weights? or has that alone been broken out without the recoil factors applied? just thinking about lead and copper bullets down the tubes we throw them down if there's a diameter that seems to spit out the most bc per grain of weight overall?

I thought I got nerdy with excel and studying, I was reading old ballistics tables books long before the computers came along when I was 12, prolly explains why excel is the main tool I use now for work. Data mine and make better tools and uses of the data. Anyhow, pretty cool work you're doing.

Highest form factor should give you the best trajectory per recoil. Obviously heavier bullets will still recoil more. I could have done the full assessment of wind number per recoil with each bullet, but that is A LOT of manual data entry into a ballistic solver, so I created the averaged reference projectiles instead. Note that some specific bullets will out/underperform the wind numbers I generated.

I'd like to code up my own ballistic solver at some point so that I can quickly solve for lots of trajectories. Then I could populate the full table quickly. I could even create my own version of WEZ at that point...

 

[solarshooter]

I think it’s recoil velocity, or possibly less barrel weight and more muzzle jump. The recoil from the 22cm just feels snappier even though it’s about the same or maybe less physical push as the 6cm.

Both are tikkas in rokstock with maven rs 1.2. The 6cm is a 26” taperless 750 contour, the 22 creedmoor is a tikka contoured 24” barrel.

Recoil impulse "shape" or "feel" is something we don't talk about enough. One of the biggest things I noticed shooting with a suppressor is the way it smooths out the recoil impulse and makes it less "snappy" and more "squishy" or "progressive".

 

[Stinky Coyote]

it's official, there are levels to this ballistics nerd game and I'm left wanting , good stuff solar shooter

 

[Stinky Coyote]

Recoil impulse "shape" or "feel" is something we don't talk about enough. One of the biggest things I noticed shooting with a suppressor is the way it smooths out the recoil impulse and makes it less "snappy" and more "squishy" or "progressive".

someone here posted at some point a comment about that difference in a sport weight 308 being just enough that the can changing the pulse was enough to start catching impacts in the scope...was that you? I hung onto that as I want a can for my 308 when we join as the 51st state it may be first on my list lol