Ballistic Coefficient: A Real World Example

I’ve blabbered about this gun and these two projectiles enough so I’m not going to make them the focus…

Last week I doped out 10-300 yards, comparing a pellet with a BC in the 0.046-0.049ish range, to a slug with a BC in the 0.09-0.1ish area. This was about a 6 hour project, spread over two days. The dope was actual on-paper results from 10-130 yards, and then on small dirt clods from 130-230 yards, and then using assistance from ballistics apps and continuation of the trajectory curve seen from actual results, to get those last 70 yards. Conditions weren’t amazing, but I shot enough of both the pellet and the slug at the various distances to have a fair level of confidence in the results.

Scope height over bore is null in this comparison (same gun, same scope, same barrel). Starting FPE is also fairly similar, just shy of 35 fpe with the slug and just shy of 30fpe with the pellet. Nearly the same average speed from both, 900-915 with the slug, and 910-920 with the pellet. Scope zero worked out to essentially 30-50 yards for the slug (2/10 mil hold-under for 37-40 yards) and 30-40 yards for the pellet (no hold-under). So pretty much the same scope zero.

The main differences in this comparison are of the BC, with the slug having roughly double the BC of the pellet.

Here’s the data, in the dope sheet-stickered-to-bottle format. Left column is distance, middle column is clicks (1/10mil) for the slug, right column is clicks for the pellet. (yes, combo of holdover and clicks to get to some of those farther distances).

1741213104129.png




Everything is fairly similar out to about 45 yards, at which time the slug starts to pull away, requiring less holdover. By 100 yards the pellets require more than a mil more elevation than the slug. By 150 yards the difference is almost 2 mils (1.8). At 200 yards, there’s more than 3 mils of elevation difference (3.3). And at 300 yards there is almost 9 mils more holdover required for the pellet than for the slug (8.8)! The pellet is quite literally dropping out of the sky at that point. One might even say that the slug shoots flatter than the pellet. ;)

As for fpe retention. I added two columns to illustrate that…

1741213160303.png



By now, this shouldn’t be news to anybody in the industry, but SEEING it, is still quite thought-provoking. It also makes much more sense now that I can reconcile the numbers on paper with how many pass throughs I get on prairie dogs even out to 150+ yards.

And we’ve certainly got an orders of magnitude effect at play. In my little comparison, we’ve got a 34.9fpe projectile still quite dangerous out to 400+ yards. (11.7fpe left at 400 yards for mine). That fpe is all I want or need. But scale up the power levels to 100-120 or more FPE, and the even better BCs that are available from some of the .22 slugs these days…and you’ve got to be concerned about anything for what? Something like 1300-1400yards downrange? Or roughly 0.75 of a mile. That’s of course max range and with something like a 30 degree angle, similar to what we’d see if we were shooting starlings or euro doves out of a tree.

I apologize for the tangent, didn’t mean for this to be a “the sky is falling” but rather a reminder that….

BC is king.
 
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I’ve blabbered about this gun and these two projectiles enough so I’m not going to make them the focus…

Last week I doped out 10-300 yards, comparing a pellet with a BC in the 0.046-0.049ish range, to a slug with a BC in the 0.09-0.1ish area. This was about a 6 hour project, spread over two days. The dope was actual on-paper results from 10-130 yards, and then on small dirt clods from 130-230 yards, and then using assistance from ballistics apps and continuation of the trajectory curve seen from actual results, to get those last 70 yards. Conditions weren’t amazing, but I shot enough of both the pellet and the slug at the various distances to have a fair level of confidence in the results.

Scope height over bore is null in this comparison (same gun, same scope, same barrel). Starting FPE is also fairly similar, just shy of 35 fpe with the slug and just shy of 30fpe with the pellet. Nearly the same average speed from both, 900-915 with the slug, and 910-920 with the pellet. Scope zero worked out to essentially 30-50 yards for the slug (2/10 mil hold-under for 37-40 yards) and 30-40 yards for the pellet (no hold-under). So pretty much the same scope zero.

The main differences in this comparison are of the BC, with the slug having roughly double the BC of the pellet.

Here’s the data, in the dope sheet-stickered-to-bottle format. Left column is distance, middle column is clicks (1/10mil) for the slug, right column is clicks for the pellet. (yes, combo of holdover and clicks to get to some of those farther distances).

View attachment 544455



Everything is fairly similar out to about 45 yards, at which time the slug starts to pull away, requiring less holdover. By 100 yards the pellets require more than a mil more elevation than the slug. By 150 yards the difference is almost 2 mils (1.8). At 200 yards, there’s more than 3 mils of elevation difference (3.3). And at 300 yards there is almost 9 mils more holdover required for the pellet than for the slug (8.8)! The pellet is quite literally dropping out of the sky at that point. One might even say that the slug shoots flatter than the pellet. ;)

As for fpe retention. I added two columns to illustrate that…

View attachment 544456


By now, this shouldn’t be news to anybody in the industry, but SEEING it, is still quite thought-provoking. It also makes much more sense now that I can reconcile the numbers on paper with how many pass throughs I get on prairie dogs even out to 150+ yards.

And we’ve certainly got an orders of magnitude effect at play. In my little comparison, we’ve got a 34.9fpe projectile still quite dangerous out to 400+ yards. (11.7fpe left at 400 yards for mine). That fpe is all I want or need. But scale up the power levels to 100-120 or more FPE, and the even better BCs that are available from some of the .22 slugs these days…and you’ve got to be concerned about anything for what? Something like 1300-1400yards downrange? Or roughly 0.75 of a mile. That’s of course max range and with something like a 30 degree angle, similar to what we’d see if we were shooting starlings or euro doves out of a tree.

I apologize for the tangent, didn’t mean for this to be a “the sky is falling” but rather a reminder that….

BC is king.

What pellet make/model/weight did you chart?
 
Unless you are shooting on a windy day with the wind varying a lot, BC will not help your group sizes, that is much more complex.

Disagree, somewhat.

Sure, in a completely wind free situation, a low BC pellet can group well, even at distance. Those conditions are rare and fleeting.

Hunters/pesters and competitors (and the industry) gravitate to high BC projectiles because it's simply easier to hit what you're aiming at with higher BC projectiles. The greater the target distance, the more we see this effect.
 
I agree that there simply isn’t any way to fully account for wind variances at these distances. So it does help for that non-ballistic reason.

But it’s a good thing to test: on any not-calm day make several attempts with both projectiles to shoot your best group at 100y while accounting for wind. The better BC round will probably win. Or maybe it won’t! Because BC variance is also important.

I recall doing a very informal benchrest shoot at the PA 1000y club. It was breezy and unsteady and most shooters were shooting 6, 6.5, or 7mm cartridges. I was set up with a 300wsm and while it was well tuned and I shot it well, I’m sure a large part of my high placing came from the BC advantage of that round on that day. In calm conditions I suspect the 6s would have caught up completely.
 
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I agree that there simply isn’t any way to fully account for wind variances at these distances. So it does help for that non-ballistic reason.

But it’s a good thing to test: on any not-calm day make several attempts with both projectiles to shoot your best group at 100y while accounting for wind. The better BC round will probably win. Or maybe it won’t! Because BC variance is also important.

I recall doing a very informal benchrest shoot at the PA 1000y club. It was breezy and unsteady and most shooters were shooting 6, 6.5, or 7mm cartridges. I was set up with a 300wsm and while it was well tuned and I shot it well, I’m sure a large part of my high placing came from the BC advantage of that round on that day. In calm conditions I suspect the 6s would have caught up completely.
The Ultimate Field Target matches at Phoenix Rod and Gun Club have provided an interesting method of comparing.

Matches began around 2020. My first match was with the .22/18.13grain JSB pellets, and I have yet to score that low again because that was the last match I used such a low BC pellet. At that time Ialready had enough time in sub20 fpe field target that I wasn't knew to the concept of field target...ie the misses weren't for lack of experience. Everyone else that has since used that (or other similarly low BC pellets) has scored low. Targets at UFT matches go out to 100 yards. Historically, the .22/25.4grain Monster RD has probably been the pellet with the most successes at these long range field target matches. We haven't seen many shoot the new AEA/JTS .30s with the BCs in the 0.07+ realm, but I'm fairly certain they would be the highest scoring pellets on the farther targets.

Similar trends have developed in the exhibition games on paper (EBR/RMAC/PA Cup). The highest BC (pellet for those matches) is what guys are using and winning with.

I have 250+ yards off my back porch, and have also sent A LOT of projectiles at long range prairie dogs over the last 10-12 years. Living in a high desert environment gives instant feedback (dust clouds) marking the pellet impact (wind drift). BC and drift and wind speed have directly correlational effects. BC goes up, drift goes down. BC goes down, drift goes up.

High BC is what a guy wants for long range airguns, if hitting the intended target or shooting small groups is the desired goal.
 
I can agree that BC doesn't equal accuracy.

BC definitely makes it easier to get that accuracy though, by minimizing wind drift, and therefore reducing the importance of reading the wind and holding accordingly.
You are talking about accuracy, where BC will have an effect. I was talking about group size, or precision in US nomenclature, which is not the same thing as Bryan Litz explains in his book.
 
You are talking about accuracy, where BC will have an effect. I was talking about group size, or precision in US nomenclature, which is not the same thing as Bryan Litz explains in his book.

Semantics aside....

Okay groups. 5, 10, 15 shot groups at 100 yards in realistic conditions.....177/8.44grain pellet is going to print a larger group than a .22/25.4gr or a .25/34gr. And a good barrel/slug combination of a yet higher BC will be even smaller group size.

Edit:
Unless you are shooting on a windy day with the wind varying a lot, BC will not help your group sizes, that is much more complex.

Went back and read your comments and see that we agree.
 
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Semantics aside....

Okay groups. 5, 10, 15 shot groups at 100 yards in realistic conditions.....177/8.44grain pellet is going to print a larger group than a .22/25.4gr or a .25/34gr. And a good barrel/slug combination of a yet higher BC will be even smaller group size.

Edit:


Went back and read your comments and see that we agree.
Not really semantics, differentiating between the two is very important if you want to understand what is happening.

As for the 100 yard groups in any weather conditions, to try to ascribe the differences in group sizes to BC alone is pure folly and is ignoring the most important basic ballistic properties of pellets or slugs, which will have far more effect on the projectile's behaviour than BC. For example, the aerodynamic moment coefficient is far more important for group sizes than BC will ever be at any range, yet the majority of shooters have never heard of it. For pellets, the spin damping coefficient along with the barrel twist rate is also critically important for long range shooting. There are many more affecting dynamic stability, all of which can be said to be more important than BC, which itself is a poor guide to anything much, being based on flawed basic assumptions about the changes of drag coefficient with Mach numbers.
 
Not really semantics, differentiating between the two is very important if you want to understand what is happening.

As for the 100 yard groups in any weather conditions, to try to ascribe the differences in group sizes to BC alone is pure folly and is ignoring the most important basic ballistic properties of pellets or slugs, which will have far more effect on the projectile's behaviour than BC. For example, the aerodynamic moment coefficient is far more important for group sizes than BC will ever be at any range, yet the majority of shooters have never heard of it. For pellets, the spin damping coefficient along with the barrel twist rate is also critically important for long range shooting. There are many more affecting dynamic stability, all of which can be said to be more important than BC, which itself is a poor guide to anything much, being based on flawed basic assumptions about the changes of drag coefficient with Mach numbers.

Please reread posts #8 and #10.
 
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Based on the last two posts I'm thinking I should back up a bit...

Working under the assumption that a guy has muddled through the various projectile options and found a projectile that the barrel likes, ie accuracy and precision.....THEN it becomes a matter of BC. Higher BC projectiles outperform lower BC projectiles. Dig through any match reports for airgun events and if you can find lists of projectiles used you'll see that, of the projectiles allowed in that particular competition, the ones with the the highest BCs will most often be the one used by the winner.

"found a projectile that the barrel likes, ie accuracy and precision" is likely due to some combination of the alphabet soup above, ("aerodymnamic moment coefficient," "spin dampening coefficient,", etc) as defined by those in the field of theoretical ballistics. I'm more of a "shoot a bunch and see what happens in the real world" kind of guy. It works for me cuz I enjoy shooting.

Found two (or more) projectiles that your barrel likes? Go with the one with the higher BC and you'll be pleased at how much easier it is to hit your target (whichever word you like to use for "hit your target").

Gravity, and it's conveniently consistent nature, is easier to account for than wind AND gravity. High BC projectiles don't turn off the wind, but they sure make it easier by minimizing the hold off necessary.

In short, assuming accuracy and precision is there, ballistic coefficient is the (current) best proxy we have here in the real world, for a pellet/slugs ability to "buck the wind" and continue on its trajectory. Is BC perfect? No.
 
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This is a fascinating discussion. Begs the question, why are lead free pellets less accurate? If it's just a game of BC and ammo weight, can't you compensate by going up in Caliber?

BC isn't as simple as weight and caliber. There are some aspects of pellet design (ratios, and shape, and weight distribution) that affect the BC. Barrel rifling can also affect the BC. As can elevation and humidity, etc.

For example: the pellet charted in my original post here,, the .20/15.89 has a BC higher than what's usually reported for the JSB .30/44.75. The .30 is almost three times heavier, and of course larger in diameter.
 
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