thoughts about pellet wind drift

The difference in seating force is due to differences in head diameter that are less than a thousandth of an inch, so maybe my argument about greater groove engraving for larger diameter pellets doesn't make quantitative sense? The difference between the rifling grooves in the JSB and AADF pellets in the photo may be more due to differences in pellet shape rather than seating force.

John,

There's a BUNCH of things mixed up here, so, let's try some "thought experiments"

Rifling profile's effects.- Pellets, in a 1/16" twist, exiting at 800 fps, make for a rotational speed of 36,000 RPM's.
The rifling depth of a typical airgun barrel is about 0.006" total after the choke.

¿Do you really think that surrounding air will have time to "drop into the grooves" ?

So, no, rifling depth has no bearing on the stability of a projectile. Once you have achieved the "non-skip" state, the depth of the rifling is irrelevant, EXCEPT when the depth is UNEVEN, and then it is not the depth but the unevenness of the rifling what creates problems.

A "tight" fitting pellet will not engrave "deeper" than a loose fitting pellet AFTER THE CHOKE, in part, that is what the choke is there for.
IF a pellet exhibits, after the choke differences in engraving, then the issue is the pellet SHAPE (dictated by the die, that is what is different when lots are changed).
What you are seeing is not "deeper grooves", but LONGER grooves that come from a slightly different shape. If you measured the groove diameter, I am sure it would be identical in both cases.

The difference between the JSB's and the AA's is MOSTLY in the skirt punch, which changes the center of gravity of the pellet, the Center of Pressure is dictated by the die, that dictates the shape.

Your MV loss is not typical, 2.5% is a bit much. I would tend to think that typical in a comparison between H&N and JSB/QYS, but between AA and JSB, seems a bit much. It is, in fact, enough to change the harmonics tune of your barrel. So, if you plan on shooting those new pellets seriously and extensively, I would start there.

Pellets do not need that much stabilization from the external ballistics standpoint, but they DO NEED a very high gyroscopical inertia to pass through the "mushroom soup" of air that wraps around the pellet at the moment of exiting the muzzle.

I've been doing some testing with Poly barrels, and, as long as the crown promotes a WIDE spread of the mushroom, they are better with slow twists.

You know that your LGU is more accurate WITHOUT the resonant cavity end plug. Why? because that particular rifle has something in the choke that skews the oscillations of the skirt. Mine was not that bad, but the moment I inserted diverters into the resonant cavity, it became much more stable and consistent.

MOST of the BC of a pellet as it comes out of a specific barrel is determined by how SMOOTHLY the pellet is released and how bad the crown concentrates that "mushroom" of air into the pellet's path. IF the pellet comes out with no "additional motions" (Precession, Nutation, and Yaw), then the BC will be substantially higher., WHY? because the SURFACE that the air "sees" as the pellet travels through it is smaller than the case where there are additional motions; and the pellet is "asleep" and turning ONLY on its own axis.

Wind drift depends on the BC because wind drift is proportional to velocity LOSS. The higher the difference in velocities between two points the higher the drift for that particular part of the range.
AND the BC's of pellets tend to go up, as velocities come down.

If you put those two together, you find the reason why so many top shooters shoot at 10½ ft-lbs. With the traditional pellets, this means shooting at around 740 fps, where is where there is an interesting inflexion point in the drag curve.

Lastly, I would remind you that the "Head diameter" in the JSB tins, is not really a measurement of the head diameter. Is the size of barrel where that lot has proven to be most accurate.
Is it a valuable bit of information?  as long as you keep within the same lot and brand, yes. But it does not "transport" across brands or lots.

I have found that QYS pellets that are labelled 4.50 shoot very well out of barrels that shoot well JSB's in the 4.52 size, AND the H&N 4.51 size.

AFAIK, both QYS and H&N DO measure the head sizes and label the tins according to actual head sizes, JSB does not. JSB labels the tins as their actual tests applied to each lot tell them to be the best application.

There are so many variables that the bottom line is: Do not argue with reality.
If a pellet batch shoots better than all others, stock up on those and shoot them for the important competitions, select the next "less good" for the local competitions and use the rest for practice at home.

One last note: The best way to deal with wind drift is to make sure that you absolutely nail the range and the vertical POI of your pellet. This will give you the most leeway in making slightly off estimations of wind drift.

😉

Keep well and shoot straight!

HM

@hector_j_medina_g 

Hi Hector,

Thanks for the expert analysis! The pellets in the photos were pushed through the choke and it was harder to get AADF through. I assumed that the pellet head slightly underfills the bore (even at the choke) and doesn't quite extend to the groove diameter, but if the pellet fully fills the bore, than the engraving groove depth in the pellet will just be the height of the lands, which indeed is independent of the pellet head diameter. I now see that my assumption was probably wrong! I wasn't talking about rifling depth affecting stability but twist rate, which powder burners have to worry about when they're choosing barrels for a favorite projectile, or vice versa. A barrel twist rate of 1 in 16" seems really fast for puny 8.4 gr pellet, but I never thought about getting the pellet safely through the mess of air at the muzzle. I'm going to double check the values for the MV drop to make sure I didn't exaggerate. Excellent point about the inflection point in drag curve near 740 fps and higher BC at lower MV! I didn't know that JSB defines head diameter differently than other manufacturers! Very interesting! Also, good point about getting the elevation right! The other day I was think about how much easier FT would be if the kill zones were square!

In the final analysis, I always turn to empirical evidence (after all, I'm an experimentalist and a big supporter of reality!), but it's nice to have some idea of what is going on to guide the decisions that we make.

I learned a lot from your reply (as usual) and appreciate the time you took to answer my questions.

Thanks,

John

John;

My pleasure, thanks for reading!

Just to add some detail that I couldn't add in my previous response as I was about to get out of the house.

The Poly L-W barrel I was experimenting with ended up in this rifle:

https://www.ctcustomairguns.com/hectors-airgun-blog/the-cca-ssp-or-the-southpaw-super-plinker  

And it is proving to be uncannily accurate out to 45 yards, printing groups of 1" or less from the bench and in relatively heavy/swirling wind.

Still some more tests to be performed, but the increase in efficiency given by the FFH (and reduced "surplus" air coming out of the muzzle), plus the  6° target crown seem to have added a lot of performance to the system. There is no "muzzle piece" in this little rifle.
The rifling in this barrel is 1 in 36" (1 in 915 mm's), so real slow.
AND, it works! LOL!

The barrel does seem to prefer MV's well above 750 fps, and it has no problems with the 9.56 gr's pellets.

This may mean that I need to figure out a way to get a springer where I can change the barrel.

😉

Keep well and shoot straight!

HM

@hector_j_medina_g  I recommend you focus on finding your best wind prediction vice a focus on cause and effect.

I had a poly barrels  that was very accurate with JSB 8.4's. I later realized I cut the wrong end off the barrel when I shortened it, meaning it had no choke.

That barrel was superb, until I used up that lot of pellets. Then it was garbage. I couldn't get  anything to shoot in it.

There are no hard and fast rules about what makes a rifle/pellet combination accurate. Crazy stuff can sometimes work great, but one shouldn't make generalizations from those successes.

The biggest take away I have is that if you absolutley nail your drop curve it'll lead to the most accurate wind predictions. Beware, however, that software can have multiple viable drop solutions. Wind prediction will be best for the solution nearest to your actual BC. 

Everything starts with an accurate velocity.

K

@knobs 

Thanks for posting that.

It absolutely proves why, unless you are shooting slugs, it is a really good idea to shoot with choked barrels.

Your unchoked barrel may possibly be used to make a slug gun, I hope you didn't throw it away, LOL!

I agree with you that the best predictor for YOUR wind drifts is YOUR MV and YOUR BC's (yes, plural).

And I also agree that the best use of your time is to use actual/real results from YOUR system, than trying to use the "one size fits all" approach of conventional software. I've always believed that and that is why PP Calc was born, it does predict very well the drift, when the data fed makes sense. I've also been saying for years that the BC is just a scale factor that, for our purposes, scales two completely different things(like scaling a Hyrax to an Elephant), so, that is why you need to use different BC's by sections of the trajectory.

"Accurate Velocity" can have two meanings:

a) A velocity at which the gun is PRECISE

b) An accurately measured Velocity

version a) is not that hard to nail down to the third digit because, on one hand there is no third digit, LOL! and once you get a system working consistently out to 40-55 yards (½" - ¾" vertical dispersion), odds are you are good to go. You may need to tune your harmonics and revise your sighting equipment arrangement, but the powerplant is good to go.

version b) is somewhat of a problem because there can be as much as 5% difference in the readings between different chronos.

AND, the current "faith" in radar driven chronos is misplaced, they are no better nor worse that the ones using lightscreens.

My tests with different chronos of current manufacture tell me that the present "state of the art" is about a 2.5% deviation/difference between the outermost liers (or should it be "liars" LOL!), with most falling within 2% of each other.
It has now become MUCH easier to read the MV than it used to be, but, if you want to have useful data simultaneously from the chrono and the target, you're better off using the lightscreen/tripod type chrono that does not affect the muzzle or the pellet's exit.

Now, after many years of telling people that the last swageing die in the life of a pellet is the barrel itself, I think I have narrowed down the causes for pellets exhibiting different BC's from different barrels: the "additional motions" are the ones that contribute the most to the different BC's, especially at the short range/high velocity section of the trajectory. As the pellet moves forward, the linear velocity decreases at a much faster rate than the rotational velocity does, and so there is more danger of "overstabilization" in the pellet world, than of "understabilization".
Which is where slow twist rates come in.

I am now looking into some research that seems to obviate the need of a BC for trajectory and drift calculations, but we're still in the early stages and I will need some help from people with better grasp of the maths involved.

We'll see, there is no end to how interesting the "humble" airgun can be.

😉

Keep well and shoot straight!

HM

@hector_j_medina_g  The new Garmin Xero Pro's are extremely accurate. Factory calibrated to +/- .1% using highly accurate reference radars. It also uses  digital signal processing software that weeds  out noise and increases edge detection that is very important for subsonic   and airgun projectiles.

The most accurate light chrony I'm aware of is the Caldwell, claiming and accuracy of +/- .25% calibrated by projectiles of know velocity.

Both chronies must be properly set up to achieve the best field accuracy.

As one would expect the two chronies do not agree. Part of that problem is the result of the statistical variation that results from small sample sizes I use  for typical readings. (10 shots)  This isn't something I can find a practical way to correct because it requires far to many shots to get a 95% confidence in the outcome. ( possibly over 125)

Brian Lititz has tested the Garmin. He's found agreement of 2 fps between different units even for high velocity centerfire rounds. That implies factory calibration that is pretty good. He also found that the Garmin outperforms both the labradar and magnetospeed chronographs.

What I find is that the trued up BC's I get using the Garmin velocities are .023 for JSB 8.4's while the higher Caldwell velocities true up to BC's of .018. That's for a pellet with a 30 shot ES of 15.6, SD of 3.6, and vertical 10 shot spread of under 3/8" at 55 yards

As you know JSB 's advertised BC for the 8.4's is .026. Both BC's predict the same effective drop curve for the pellet.  The difference is in their wind predictions. I can't tell you which one is right. I can tell you which one I'm going to use. That's the part that each shooter has to figure out.

Regarding non BC predictive applications, one can do that with  Excel using measured drops and curve fitting. No scope height, velocity, or BC required. I've got it to match ballistic software to within a click in the past. What it can't do is adjust my drop chart on the fly for large changes in density altitude or velocity variations that might spring in the field. I'll be curious what you come up with.

K

@hector_j_medina_g 

I measured the MV difference between AADF lots 34 (new) and 13 (old).

 I alternated 5-shot strings between the two pellets (shot with my LGU using the Garmin chrono):

The difference between the two 15-shot average is around 11 fps. Although my LGU shoots pretty well with the new lot, you can see in the target (bench-rested 5-shot groups at 20 yards) below why I was so fond of lot 13!

The standard deviation was significantly lower with lot 13 (although, as long as the SD is below ~5 fps, I haven't noticed much correlation between SD and accuracy). Unfortunately, round-headed pellets don't cut very clean holes, but I think that this target shows that with lot 34, every now and then a pellet goes a bit astray whereas with lot 13 they all pretty much all go through the same hole at 20 yards.

So we're below 2% difference between lots of AADF, so I guess it's within expectations. In my springers, I see a very strong correlation between MV and how tight the pellet fits in the breach (tight fit means lower MV).

Best wishes,

John

@knobs 

I also like using curve fitting in Excel. In my elevation table I use no physics at all (except assuming that the pellet height is a smooth function of distance). Every time I practice, I check my POI at standard distances, and  put the height differences in an Excel spreadsheet. Then I do a 4th order polynomial fit and Excel spits out my range table from the fit. With time, the differences in POI and POA tend to get smaller and my table converges to values that are pretty reliable.

Of course, as K said, this doesn't allow the table to be quickly changed when conditions change. During sight-in at FT matches, I try to look for POI/POA differences at most of the standard ranges and just write the corrections on my table. I'm not sure this is the optimal (or even a good?!) way to do things but I'm pretty sure that I have other areas where I'm even worse (like wind reading and the positionals) so I'm going to work on those instead.

Best wishes,

John

@knobs 

Until a manufacturer presents me with his NIST certification with the deviation showed vs. the National Reference Ballistic Chronograph, for ME, it's all vaporware. And if you are interested, this short note will illuminate the bullet's path (pun intended):

https://www.nist.gov/laboratories/tools-instruments/reference-ballistic-chronograph  

It's easy to claim a certain accuracy, but you need to explain vs. what and which part of the whole process you are certifying. Calibrating vs. ""highly accurate reference radars" seems a bit circular for a solid argument.

Problem with radars is not speed of reading, it's accuracy when the projectile's foot print is small. I still need to receive assurances by any of the radar Chrono makers that they can read a 0.177" pellet beyond the 44 yards line (40 meters). When that time comes, I'll jump in and buy one.

In any case, a difference of up to 2% will not make too much difference. LOL!

Not only does BC's change with velocity, since velocities depend on atmospheric variables, and those are totally random, to pursue the finding of the "ultimate/most precise" BC is, to me a futile endeavour.

Again, PP Calc was born from that conviction, and from the need and want to allow shooters to "adjust on the fly". Your comment reminded me of Ray Apelles, that had a very effective way to do this (he even sold his software, but never did really catch up), IIRC, he used a variation of the Pejsa method, and he once put to test my PP Calc. We came to within one click over the longest range (in his case 75 yards) LOL!

Now, your BC's re-affirm my conviction that PCP's are easier to shoot 😛

I have shot thousands of pellets through different rifles in controlled conditions and no pellet/rifle combination has ever come up with a BC higher than 0.019

My most reliable set, through several thousands of shots, gives me BC's of:

0.0156 @ 9 M

0.0174 @ 41 M

0.0190 @ 50 M

And this gives me an average error of 0.06 mRads  over the whole trajectory.

This is with the QYS 8.49 Streamlined (similar to H&N's "Baracuda 8", but more efficient).

What I am looking at now is a way to backtrack some sort of ballistic constants, from a Third degree polynomial. IF that works, then we can have a direct drag of the pellet and the need to go through the BC will be eliminated for all calculations. It's an effort that is in its infancy, but seems to hold promise. IF it works, then there should be a way to put it into an app.

IMHE cubic fittings work better than fourth degree fits, but John has been using the fourth power and he likes it. Anyway, to each his own.

Keep well and shoot straight!

HM

@johnc 

I would tend to interpret your chart a bit differently:

It seems that you started from a "Cold bore", which in springers, usually means a high MV.
Shots 1 to 3 settled the powerplant and from there on, you clearly see a creeping up of MV's for lot 34.

Lot 13 stays pretty much the same, though it was the lot that was shot AFTER the lot 34's first five.

So, while Lot 13 stays the same, Lot 34 creeps up. This would mean, to me, that you have a slightly different ALLOY in the pellets and the barrel is either getting into that, or getting out of the alloy of lot 13.

And here comes an added variable: the content of Sb is low in most pellets (under 2.5%), but a difference of 0.1% can make the pellet appreciably harder. So, it may be that it's not a different head diameter, but just a different alloy.

In my guns I do not see a correlation between pellet fit (when inserting) and MV's because the way my guns work is that they "seat" the pellet always to the same spot upon closing the action.

And this suggests me two experiments you should do, given that you are the expert experimentalist:

1.- Repeat the test, but lube with Pledge and bake your pellets for 3 mins at about 350° F per 500 pellets if starting from cold or 2 minutes if it is the second or further batches.

2.- Seat your pellets with a spherical object of 7 mm's diameter.

You can invert the order of the experiments, just don't them at the same time, LOL!

That will give us a bit more info.

Keep well and shoot straight!

HM

@johnc 

We had talked about the third vs. fourth order polynomials. So I am going to send you in an Email a paper that merits your reading.

And we can talk about that in Ohio (I assume you are going to the Steubenville GP).

Keep well and shoot straight!

HM

@hector_j_medina_g  The Garmin is only designed to return muzzle velocity. Tracking out to 44 yards isn't necessary, although if that's your personal standard, I'm good with that.

It sounds like you're going to attempt to integrate a solution using the Cd curve so you'll have live drag across the trajectory?

K

@knobs 

Yes, I know the limitations of the "short" radar readers. I understand their use in firearms from the POV that you do not need to wait for a cold line to setup your chrono when shooting at targets, but I think it is overspending for airguns. JMHO
The 44 yard line is the "current state of the art" in real terms. Tests performed by others and published. For me I would need to be able to read the speed of a 0.177" cal pellet at 55 yards with absolute consistency to be happy.

Yes, the idea is to have a REAL drag curve, that is why the long range readings of the velocity are AS important as the maths developed to approx the whole thing with a cubic polynomial.

The eternal theory-practice-theory-practice cycle.

😉

Are you going to Ohio?

I have a whole house to my own from Friday night to Monday morning, LOL!

Keep well and shoot straight!

HM

The main thing which I have wasted the most time on in trials is muzzle velocity radars. We always had two operating, one each side of the gun barrel near the muzzle, or further back if the gun had a muzzle brake, and they had to agree to within .3 m/s, which, with small arms, was challenging. The units we were using were ten to twenty thousand dollar units. The only way of using them was to extract the raw data from the units and to curve fit the data ourselves to obtain accurate muzzle velocity values. The majority of the trajectory was tracked using a multi-million dollar Doppler tracking radar, which had to be transported on a low loader.

This is why I do not like the idea of using radars as chronographs for airguns. I do have a LabRadar, but only because you can get a file with rawish data, which you can then analyse yourself. I use a Nate Chrony in conjunction with the LabRadar to obtain data over the trajectory. Radar manufacturers would try to produce their own analysis, but it was never satisfactory for our purposes. I would not buy any radar which did not permit the recovery of the raw data. I always want to know what data they have used and how they have used it before accepting their results. Many of the units will still give you a number no matter what range they have managed to track to. This is why the claimed accuracies are a nonsense, as it will depend entirely on the number of data points collected and the range over which they have been collected, and this will be critically effected by the setting up of the units and what else is around the area you are shooting in. We found that for small arms, small changes in the position of the radars and the angles they were looking at could give large changes in the matching of the muzzle velocities. I was lucky in that when I was using the radars, I had professional instrumentation engineers helping me, one of whom was a recognized world expert in tracking gun launched projectiles.

Deep rifling grooves act like paddles and spin up a ring of air around the pellet, giving it a bigger profile for the wind to push on. Just a thought.

@james_perotti 

James, I think that it is not exactly like that.

Think of this:

Imagine a paddle that can return so fast to the original position that the water that WAS in front of the paddle has not yet returned.

Against WHAT is the paddle going to push?

The grooves in airgun barrels are mostly in the 0.002" to 0.003" deep (each side), the choke may add half a thousandth. AND they are spinning at around 30,000 RPM's (when shot from a 1/16" twist at roughly 800 fps).
Airplane propellers normally have a limit of 3,000 RPM's, and our pellets have SUBSTANTIALL smaller "paddles" and rotate 10X faster. Faster the 3,000 RPM's airplane propellers are not very effective.

It is when the pellets have "additional" movements (Nutation, Precession and Yaw) when we get the effect you mention, THESE add a "ring" of lead that increases the caliber and that is what reduces the BC.

Lastly, remember that pellets are FLANGE stabilized projectiles, meaning that the skirt is traveling in a "cone of vacuum" that is created by the head. IF the skirt leaves the center of that cone, it is pulled by the other side and stabilized. That is why WC pellets do NOT NEED a rifling if they are shot under 500 fps. The rifling is there to overcome the effects of the "Mushroom Cloud" that is produced when high pressure air overtakes the pellet.

Like this:

The difference is that this bullet is traveling substantially faster than most pellets, and so the bullet is ALMOST clear of the mushroom. Pellets will not even start to clear it.

Quite a lot of "state of the art" airguns are now using barrels with twists in the 900 mm's region (about 35").

Trick here is to ensure that the air at the muzzle is "diverted" away from the pellet's passage in an opportune and effective manner.

Keep well and shoot straight!

HM

@miles_m 

Thanks for reading, Miles.

Up to the last weekend, I would have agreed wholeheartedly with you. My tests of the original Garmins, LabRadars, and others were not particularly enticing.

BUT, last weekend I had the opportunity, afforded by my good friends that were shooting the Sherwood Forest GP, of checking a Garmin Xero (latest version), vs an Athlon Rangecraft at the range, and then compare those velocities with my "trustworthy" Caldwell Precision Chrono at home.

I used my CCA D-54 shooting at around 777 fps. With my Caldwell, a 20 shot string yielded an average of 775.2 ± 2 fps

The Garmin yielded an average of 766.3 fps and the Rangecraft yielded an average of 763.1 fps

Now, the difference in altitude between home and Sherwood Forest (Ohio, not Nottinghamshire), is about 1,000 ft. So it falls exactly into the 0.125% per 1000' of change for the D54 platform that has a 28 mm's diameter piston, and so is more stable as pertains to the altitude changes.

Now, Why do I trust the Caldwell? because when I was building BB guns for the Law Enforcement Agencies  ( https://www.ctcustomairguns.com/hectors-airgun-blog/first-the-army-now-the-two-top-leos-of-the-nation), the Ballistic Research Facility tested with their Oehler 36, the MV's that I quoted, finding them in acceptable correlation (that means within 0.5%).
AND that Oehler 36 is routinely calibrated vs. the Reference Ballistic Chronograph ( https://www.nist.gov/laboratories/tools-instruments/reference-ballistic-chronograph) at the NIST.

So, while not a certification of any sort, it does give me the "warm and fuzzies" that my Caldwell Chrono is not shabby at all.

In the 8 years that have passed between the introduction of the original Garmin Trainer, the 11 years that have passed since the introduction of the LabRadar, and the current production of radar Chronos, there have been substantial advances, MOSTLY in the firmware. When you say that the main "gist" is how to interpret the raw data, you nailed it, my friend.
These firmware advances have taken large strides towards producing useful and real field-worthy information.
And, the rapidity with which the Athlon Rangecraft produces a reading is really eye-opening, twice as fast as the Garmin, at least.

Now, that does not mean I am going out and buying one. ROFL! As a gunsmith my main use of the Chrono lies in making sure the guns I sell are legal for the competition (not legal as in your case, but still...), or "Fit for Task/Purpose" in other applications. And in that sense, the Radar units still do not give me any advantage for the day to day use in the shop.

I do have to say that I may start to take the CALIBRATED QiuFeng to competitions, with the suitable adapter for my piston airgun, as what we did see at the official Chronoing station was not quite as it should be.

Not that I live by the Chrono, but it WAS comforting to know that I was using the wrong ballistic table on the first day (Duuuuuhhhh!!!!).
And that allowed me to do much better in the second day.

I would entreat you, as a fellow scientist/engineer, to give another look at the current versions, ESPECIALLY the Athlon RangeCraft. It was a pleasant surprise for me.

Keep well, my friend, and shoot straight!

HM

Thanks Hector, I always wondered about the skirt being in a vacuum. About the rifling grooves spinning to fast to catch any air, then are the rifling grooves in a vacuum as well?

Posted by: @james_perotti

↑

Thanks Hector, I always wondered about the skirt being in a vacuum. About the rifling grooves spinning to fast to catch any air, then are the rifling grooves in a vacuum as well?

Do note that high pressure areas are in blue/green, the vacuum areas in red. I have not found at which velocity this was made, or the specific design / shape used. So, it MIGHT  not be exactly about what we are talking about. But it gives a good idea.

The funny thing is that, regardless of the clarity of this simulation, some pundits still insist on the pellet being a "drag" stabilized projectile... go figure.

Now to your question:

If you refer to the rifling grooves in the HEAD, then there are several possibilities:

1.- You have a high quality barrel, (L-W or equivalent) that is dimensioned so that a 4.50 mm's head rides the top of the lands. 

2.- Now, let's assume that you are using a quality pellet that has been sorted by head size and labelled as 4.50 (H&N FTs or QYS's)

If 1 & 2 are true, then the rifling marks on the head of the pellet will be ONLY due to the choke, and they will be barely ½ of thousandth of an inch.

If 1 is true but you are using the quality pellets that are labelled by testing lots in air gauged barrels (JSB's), then the rifling marks could be between ½ and 1 thou. If your barrel likes the 4.50's.

SOME barrels like "fatter" pellets, like the Walther barrels (they usually like the 4.53's or some 4.52's), then the rifling marks will be between ½ to 2 thou's deep.

Now, IF you use a pellet with a domed, or a streamlined head, then the rifling marks of the head do NOT ride in a vacuum.

HOWEVER, if you choose any other type of head that has a "meplat" or something that works like one, then the rifling marks of the head DO ride in a vacuum.
And this is the peculiar reason why some strangely shaped pellets (Hades, BHE, BH, CrHP, etc.) MAY fly extremely well from some barrels.

The function of the meplat is to induce a controlled turbulence just at the edge of said meplat, and this allows for air to slip on air for the rest of the ojive, which offers less resistance than air slipping on lead or gilding metal (as in the case of very high quality low drag spitzer bullets). The SIZE of the meplat is an art, more than a science, and it is something that has not been fully explored in the pellet world.

HTH, keep well and shoot straight!

HM