Large BC Differences — Due to Barrel Differences? 🤔

[JungleShooter]

Large BC Differences — Due to Barrel Differences? ​

I've been surprised to experience how different barrels will have varying degrees of hold off necessary for similar wind values. All else being the same, i.e. same pellet at same velocity.

OK, I really don't like reading this. Really. Don't.
Sorry.
(Thank you to the shooter to call attention to this issue, I have nothing against you!)


What I understand from this post is that
▪ the same pellet
▪ at the same MV
▪ from different barrels
➔ suffers from a LARGE difference in its ballistic coefficient.


I acknowledge there can be SMALL BC differences from different barrels.
But LARGE differences?
I don't like that.


Because it would make published* BC numbers pretty useless:
Every barrel—projectile combination would have to be tested. Individually.
You guessed it: I don't like that....
*(by airgunners, manufacturers, anybody)



Please, I'd love a discussion on that.
And I am open to accept what I don't like.
Please, supply some arguments or some kind of evidence (drift numbers, BC tests, etc.).
Because the thing I like less than large BC differences is — to continue shooting in ignorance.

Matthias

 

[OldSpook]

Large BC Differences — Due to Barrel Differences? ​

OK, I really don't like reading this. Really. Don't.
Sorry.
(Thank you to the shooter to call attention to this issue, I have nothing against you!)


What I understand from this post is that
▪ the same pellet
▪ at the same MV
▪ from different barrels
➔ suffers from a LARGE difference in its ballistic coefficient.


I acknowledge there can be SMALL BC differences from different barrels.
But LARGE differences?
I don't like that.


Because it would make published* BC numbers pretty useless:
Every barrel—projectile combination would have to be tested. Individually.
You guessed it: I don't like that....
*(by airgunners, manufacturers, anybody)



Please, I'd love a discussion on that.
And I am open to accept what I don't like.
Please, supply some arguments or some kind of evidence (drift numbers, BC tests, etc.).
Because the thing I like less than large BC differences is — to continue shooting in ignorance.

Matthias

His "large" may not be the same as someone else's. "Large" for a squirrel hunter may not be the same as large to a benchrest shooter.

I sometimes test my BC using a chrony and STRELOK or chair gun. It isn't unusual for me to measure a 10 or 20 percent difference from published data.

 

[qball]

Hey Matthias


This is a great conversation topic because it has sooooooo many variables. It's a observation made by some people that some polygon barrels do shoot a little better in the wind. Assuming pellet and velocity and bore size AND twist rates are the same the land and groove creates shaper deformation on the pellet which will interact with the wind bit more just like anything that has sharp corners will have higher drag as something that has smooth corners like cars.

In this picture is a good demonstration of difference in deformation on pellets by the rifling. If the twist rate is higher I foresee a little bigger difference in drag and effect from the wind. Again there are quite a few variables and YMMV.


Also manufacture publish BC data is usually at sea level which means most people will get higher BC based on the elevation of your shooting location.

 

[Franklink]

While this was technically a "review," there was a lot of testing done in that review that is relevant to this topic.

BSA Gold Star "Union Jack" in .177, ongoing review

Here she is! Just picked it up today and spent some time with it after the kids went to bed. I have yet to shoot a pellet, mostly just was getting familiar with it, scoped and stock adjusted to my liking. So, this will mostly be a photo dump, with a few initial thoughts. Disclaimer: this gun...

www.airgunnation.com

Specifically post #15 and post #37

That's the best head to head that I've done. Most of the other collective experiences that created my opinion that some barrels are just better in the wind is anecdotal, from shooting in the wind with lots of barrels from lots of different guns.

And yes, unfortunately, every barrel/pellet/fps combination will produce a different BC. Even a different batch of the supposedly same pellets can produce a different BC (JSB's reputation for tweaking the pellet profiles).

I had an interesting experience in the last few months where I was shooting my long ranger with a STOUT tailwind, probably 25+mph that day. I measured BCs and they were up around 0.06 when that gun/pellet/speed configuration typically produces BCs between 0.048 and 0.052. In retrospect it makes sense though, airplanes get where they're going faster when they have a tailwind, so the pellets were retaining their speeds better that day, less air molecules to smash against since they were going "with the flow." So, even day to day differences in conditions can change the BC.

A ballistic coefficient is not set in stone, unfortunately. Also interesting to note that BC doesn't tell the whole story. Sometimes a barrel will do better or worse than you'd expect it to, even in the context of the BCs that have been collected from that combination. In that example in the link I shared above, that poly barrel doesn't have a much better measured BC than the other two barrels that it did better than in the wind.

 

[Ghostranger169]

Matthais,
I feel your pain. Closer range/higher velocity/calm conditions/larger ammo/larger kill zone shots are a bit less finicky, but farther/slower/windier/smaller ammo, smaller KZs can expose any shortcomings in assumed data(accuracy, susceptibility to wind, etc...) or assumed accuracy(from experience shooting in more favorable conditions). I had always used published data in Strelok and never saw much of a discrepancy until I tried shooting(and not hitting) at longer ranges and/or on really windy days.
I have found that if I want any type of certainty of predicting where a projectile will land(i.e.- hit what I'm aiming at) at longer distances(~85 to 200 yards) using Strelok Pro to give me a ballistic solution, then I must spend a lot of time carefully validating all the "known" ammo measurables(bullet weight, length, and diameter) of PUSHED THROUGH MY BARREL projectiles, and NOT just use what Strelok plugs in or is published. Average muzzle velocity must also be validated by long strings of shots(30 or more) at the specific fill pressures and under similar environmental conditions that I will be shooting.
Scope height must be validated as well, before moving on to validating BC(which is almost always LOWER than published values) at different distances, or using multiple BCs(for longest ranges). Also, this has to be done for each individual gun/barrel/scope combination. If I switch out barrels(same length, type, caliber) on my Crown, I often end up using a slightly different (measurements on pushed through the barrel ammo) bullet data(bullet length, diameter, weight) and BC to "true up" with Strelok Pro's ballistic solutions at longer ranges, even though I am shooting from the same tin of ammo, at the very close to the same speed. I usually only need to correct this data if I am shooting out past 80 yards. Most of Strelok's solutions are close enough for shorter distances and/or faster speeds and/or, etc...(as mentioned above).
Then, trying to measure and enter the correct values to depict how the average environmental conditions(average wind, temperature, etc...) are affecting your projectile(over the entire distance to target) while you are taking the shot bring a new set of challenges.

 

[elh0102]

We live in an age of too much information, and we have too many things that interfere with shooting. My head hurts just reading this stuff. Regardless of the information indicated by the technology, even the technoids among us are going to validate their assumptions by shooting. So, why not just shoot? The goal of all this is to hit our target, and there is only one way to find out which pellets and tuning combination will do that in any given rifle. I'm old, and I guess I just like something simple, especially when it works.

 

[rcs9250]

We live in an age of too much information, and we have too many things that interfere with shooting. My head hurts just reading this stuff. Regardless of the information indicated by the technology, even the technoids among us are going to validate their assumptions by shooting. So, why not just shoot? The goal of all this is to hit our target, and there is only one way to find out which pellets and tuning combination will do that in any given rifle. I'm old, and I guess I just like something simple, especially when it works.

elh0102,
As I was reading the posts in front of yours, I was developing pretty much the same opinion. I love to tinker, I guess more with my hands than my brain, but I find the discussion very interesting. All the variables involved are interesting. Having been in manufacturing my entire life and realizing whether a simple component or complex one, no two are the same, just like a finger print. Some features on the part that vary won’t make any difference but some do and tighter tolerances will minimize that effect. But, in things like barrel ID’s, they try to hold the tightest tolerance practical with respect to manufacturing equipment and final cost. The end user deals with the final result.
Like you, I’m old, I enjoy reading all the science but don’t have to apply it unless I want to. For me, I go to the range with my rifle , ammo, SCBA tank and set targets at what I’ll call “ethical squirrel kill distances”. For me, that’s 10-50 yds, at least at the present time anyway. Then I’ll shoot every ten yards within that distance and note it in my dope book and determine where each point of impact is on the reticle (for come ups) and then do the same thing for actually dialing up from my no wind zero and then when hunting I can choose between reticle or dial come ups. Typically the come ups are small but when working with the desired kill zone on a squirrels head, I feel it’s necessary. If my shot feels more ethical to be a heart lung kill zone, it’s a little more forgiving in size.
But even with my fairly simple method, obviously if anything changes in wind, FPS, pellet weight, pellet shape, cleanliness of barrel and me, all bets are off for that dope.
I suppose it would be a very boring hobby if you just turned knobs to specified settings, insert pellet, then shoot dead center. Cool, but all that could be done at home in the recliner without firing a shot.
I like my degree of complication but enjoy learning about the variables.
Randy

 

[Arzrover]

I've measured a good number of bc's in similar barrels with the same batches of pellets as well as different batches of pellets in the same barrel. Part of the ART project goals from my position was to select the best barrel in accuracy AND bc. Many shot sub moa but gave a little worse measured bc. It was an interesting project and really, not finished even yet for me. The thing that I had hoped to find was the WHY.... still have only a vague idea. There is something more than just bore and rifling profile.

I have an AA RN10 in 13 ft lb w jsb 8.4s that will shoot right with my 20 ft lb USFT w JSB 10.3s in the wind. This is the puzzler that I keep going back to. The USFT is a 23" LW poly and probably the best I've tested and runs right w Franklink's USFT. I have not measured the bc of the 3 but how can 8.4s at 13 ft lb blow no more than 10.3s at 18 ft lb? The RN10 is a standard rifled barrel from the early 90s and is most probably an LW.

So to me, the rifling consistency, dimensions, symmetry, and perfection of the crown, contribute, but I've seen plenty of anecdotes of measured consistency that do not do as well as others. Another aspect that is likey related is the ammo sensitivity. Some will shoot well with about everything and others only 1 or just a few. I know Mike N has put in a huge amount of time trying to understand all of this and after some conversations with Frank Walther of LW , I feel that he and his company have put in the time and can probably build that barrel... but they are adamant about not sharing secrets across the different customers own research as well as their own.

Tough puzzle and the current JSB pellet quality isn't helping. I wish other companies would make pellets as high in bc as JSB.

Bob

 

[elh0102]

elh0102,
As I was reading the posts in front of yours, I was developing pretty much the same opinion. I love to tinker, I guess more with my hands than my brain, but I find the discussion very interesting. All the variables involved are interesting. Having been in manufacturing my entire life and realizing whether a simple component or complex one, no two are the same, just like a finger print. Some features on the part that vary won’t make any difference but some do and tighter tolerances will minimize that effect. But, in things like barrel ID’s, they try to hold the tightest tolerance practical with respect to manufacturing equipment and final cost. The end user deals with the final result.
Like you, I’m old, I enjoy reading all the science but don’t have to apply it unless I want to. For me, I go to the range with my rifle , ammo, SCBA tank and set targets at what I’ll call “ethical squirrel kill distances”. For me, that’s 10-50 yds, at least at the present time anyway. Then I’ll shoot every ten yards within that distance and note it in my dope book and determine where each point of impact is on the reticle (for come ups) and then do the same thing for actually dialing up from my no wind zero and then when hunting I can choose between reticle or dial come ups. Typically the come ups are small but when working with the desired kill zone on a squirrels head, I feel it’s necessary. If my shot feels more ethical to be a heart lung kill zone, it’s a little more forgiving in size.
But even with my fairly simple method, obviously if anything changes in wind, FPS, pellet weight, pellet shape, cleanliness of barrel and me, all bets are off for that dope.
I suppose it would be a very boring hobby if you just turned knobs to specified settings, insert pellet, then shoot dead center. Cool, but all that could be done at home in the recliner without firing a shot.
I like my degree of complication but enjoy learning about the variables.
Randy

Randy, we are of similar minds, and our air rifle usage is the same. I was a competitive BR shooter for years, RF and CF, so believe me, I understand the minutia of precision accuracy. I remember being up to 3 AM preparing brass to fire form and then develop loads. I was not then retired, and that hobby got to be too much like a second job. So now I enjoy my air rifles, mostly out to 50 or 60 yards. I test enough to get a good pellet and balance the tuning around it. Then I shoot. If I miss, I get a bigger target, and life is fun!
Ed

 

[Ghostranger169]

elh0102,
I feel your pain too. I still pull out the springer from time to time just to have fun and plink like I did in my youth.
I will respectfully(slightly) disagree with the statement that "we live in an age of too much information".
While it can be taxing to wade through a mass of available information to find out which bits and pieces are relevant and which aren't, it's even more taxing to need information and not be able to have access to it. Plus, ya don't HAVE TO do anything with it(or even look at it), if ya don't want to.
I believe we live in an age where access to information has made actual knowledge(what you retain by having proven to be accurate through experience) irrelevant. The sentence: "I don't HAVE TO KNOW xyz because Google knows and I have a smart phone" gets bandied about quite a bit.
Also, we have long since lived in an age where most technologic advancements have surpassed the point of most people's ability to use them, or at least use them correctly(think all the buttons on a tv remote control). Too many options is not always a good thing.
All that being said, the main point of this thread is really just wanting to use the correct BC value(s) instead of incorrect ones, for whatever you are ALREADY using them for. And maybe open up a discussion about the how published BCs are just a "ballpark" number(perhaps measured under a singular set of conditions) and NOT an absolute.

 

[tor47]

I do not know if the OP actually measured the BC. But I have read that barrels with faster twist rates can make the pellet to "climb" or drop more, dependent on which side the wind blow from. So the BC can teoretically be the same, even if the POI is not.

 

[OldSpook]

... but how can 8.4s at 13 ft lb blow no more than 10.3s at 18 ft lb?

Time of flight? How much difference is there?

 

[Centercut]

Then we can go and throw in “vertical jump” which is a factor in addition to but not the same as or predicted by BC. The same pellet shot at the same speed can react differently when into a quartering wind from either direction from different spec barrels.

I’ve seen this when shooting both .30 caliber and .25 Heavy pellets. This is more than likely the reason FX is trying to go “back to the future” with their prototype 1:40 twist .30 caliber liner that Frederick and Hein (maybe other factory shooters) used at RMAC with great results. I’ve noticed it myself when shooting my old ST barreled .30 Bobcat compared to faster twist barrels. They’d show similar accuracy with little to no wind, but the vertical spread would be measurably less with the super slow twist ST barrel.
I’ve also noticed it with two .25 Crowns side by side. One shooting with the 1:18 Superior Heavy and the other with the 1:27 Pellet A liner. Equivalent accuracy but tighter vertical spread in gusty quartering winds for the Pellet A.
Just another factor to consider…

 

[elh0102]

elh0102,
I feel your pain too. I still pull out the springer from time to time just to have fun and plink like I did in my youth.
I will respectfully(slightly) disagree with the statement that "we live in an age of too much information".
While it can be taxing to wade through a mass of available information to find out which bits and pieces are relevant and which aren't, it's even more taxing to need information and not be able to have access to it. Plus, ya don't HAVE TO do anything with it(or even look at it), if ya don't want to.
I believe we live in an age where access to information has made actual knowledge(what you retain by having proven to be accurate through experience) irrelevant. The sentence: "I don't HAVE TO KNOW xyz because Google knows and I have a smart phone" gets bandied about quite a bit.
Also, we have long since lived in an age where most technologic advancements have surpassed the point of most people's ability to use them, or at least use them correctly(think all the buttons on a tv remote control). Too many options is not always a good thing.
All that being said, the main point of this thread is really just wanting to use the correct BC value(s) instead of incorrect ones, for whatever you are ALREADY using them for. And maybe open up a discussion about the how published BCs are just a "ballpark" number(perhaps measured under a singular set of conditions) and NOT an absolute.

You're right, I was being a little sarcastic about too much information. There are times when I take liberal advantage of the resources available. But when it comes to precision accuracy, I'm just at a point in my life in which I work in round numbers, not three decimal places!
Ed

 

[d3vnull]

Time of flight? How much difference is there?

Be careful there they didn't like that answer in 2020

https://www.airgunnation.com/threads/less-wind-drift-heavier-weight-or-more-speed.855602/

 

[Franklink]

Time of flight? How much difference is there?

Yes, you've supported your stance that a shorter time of flight gives the wind less of a chance to influence the pellet but that argument isn't applicable in the example Arzrover shared because: An 8.4 @ 13fpe is about 830fps at the muzzle. A 10.3 @ 20fpe is about 930 at the muzzle. The 8.4 was never traveling faster than the 10.3, at any point of the pellets flight path. Since the 8.4 was never going faster, it cannot have a shorter flight time, assuming they are both being shot to the same distance.

 

[Arzrover]

There is also another factor which likely changes the bc... obturation.
In my example above, both rifles had relatively small ports. In the USFT case, it's to help with consistency in an unregulated rifle. In the RN10 case, it is a design tradeoff to allow straight into the barrel loading and was never really intended for 12 ft lb and above. When the air blast is damped by the small port, the swelling or reshaping of the pellet is less than one like a Red Wolf where full bottle pressure is applied briefly to the pellet. I believe this was a large factor in CPH's doing so much better at 20 ft lb than the comparable pellets in the Premier golden era. Very little skirt to obturate and harder alloy.

So to me, a longer, softer pulse to achieve the same velocity SEEMS like it should shoot better in the same barrel by changing the shape of the pellet less. Slugs would have little change, so they would show less preference .

Bob

 

[OldSpook]

Yes, you've supported your stance that a shorter time of flight gives the wind less of a chance to influence the pellet but that argument isn't applicable in the example Arzrover shared because: An 8.4 @ 13fpe is about 830fps at the muzzle. A 10.3 @ 20fpe is about 930 at the muzzle. The 8.4 was never traveling faster than the 10.3, at any point of the pellets flight path. Since the 8.4 was never going faster, it cannot have a shorter flight time, assuming they are both being shot to the same distance.

Hence the question mark, you will note in my reply. But hey who reads for content these days expecially when a fight is so much more fun? It was just a question. That's all.

 

[OldSpook]

There is also another factor which likely changes the bc... obturation.
In my example above, both rifles had relatively small ports. In the USFT case, it's to help with consistency in an unregulated rifle. In the RN10 case, it is a design tradeoff to allow straight into the barrel loading and was never really intended for 12 ft lb and above. When the air blast is damped by the small port, the swelling or reshaping of the pellet is less than one like a Red Wolf where full bottle pressure is applied briefly to the pellet. I believe this was a large factor in CPH's doing so much better at 20 ft lb than the comparable pellets in the Premier golden era. Very little skirt to obturate and harder alloy.

So to me, a longer, softer pulse to achieve the same velocity SEEMS like it should shoot better in the same barrel by changing the shape of the pellet less. Slugs would have little change, so they would show less preference .

Bob

There is a good argument. Obturation in a pellet changes the shape of the skirt, expecially with thin walled skirts. A more cylindrical pellet would ??probably?? have a lower BC? Still what sorts of differences are we really talking about? WRT BC? Maybe the drift is driven more by spindrift than we think?

 

[Franklink]

Hence the question mark, you will note in my reply. But hey who reads for content these days expecially when a fight is so much more fun? It was just a question. That's all.

Not looking for a fight. You asked a question. I answered it.

Please don't derail this thread too. There are likely things we can all learn from the collective knowledge of the forum members.