Home Forums Hunting & Shooting BPCR Question about Mathews book

Paul Matthews wrote a book called "Wind Drift and Deceleration" in regards to Black Powder bullets/velocities...anybody here read it?

Yep!

How you like it? I read a review that commented that he takes a different track than most in analyizing drift but still gets the job done. Worth the price?

.........I've shot that original .50-90, of Dave Gullo's, at sundown, at pigs.....300meters. The one he always poses with in the catalogues, .........neat old rifle, honest as the day is long...........and really accurate.
Once I got on to the sporting sights, and hold off....If I'm not mistaken, I had to shade right.............it was an absolute riot...with a center hit, the steel went straight back into the berm....................sheer kinetic energy............The Mathew's book,If I'm not mistaken this is the one where he gets pretty passionate about hurling boxcars.......... " use the heaviest bullet practical, for the chosen caliber"

Brutal thing to shoot prone, and I would note that that the basic thesis presented, never really went anywhere,

I'm still flyin' low, and slow.......

Lot of the guys are reaching for velocity.....and I spot for 'em. WIND SENSITIVE, albeit an extremely flat group....no probs. with the vert.

I like the way low and slow, with a heavy, carves wind, and have to live with the inherant vertical.

No free lunch, ya picks yer' vels., and takes yer' chances.

GTC

Dan; the book is not very thick, but I found it to be interesting and informative. A lot of it is way over my head, but quite a bit 'trickled' down to my brain as it passed over <img src="/ubbthreads/images/graemlins/crazy.gif" alt="" />
Good read and piques a lot of thought. I do not regret buying it and occasionally peek back into it.

Thanks, been toyin' with the idea of picking up a copy. <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />

Crossfire, interesting way of puttin' it...



...he do don't he? <img src="/ubbthreads/images/graemlins/grin.gif" alt="" /> Don't mind a little of that now and then myself.

............Hell Dan, I'll lend you my copy, Pm me with a snail mail addy (........This is cool, one year into this, and slingin' all the internet slang / jive.)

Really, it's a loaner, if you'd like to check it out.....our idea of a" light" bullet, in .45 cal. .........starts around 440 gr., so this can take a bit of gettin' on to.

I'll be " loafin" 550 gr. beauties, at a scorching , low vel, 1140, at tomorrow's match, in Tucson........the " screamers".......................? warp speed, 1300-1320fps......

Low and slow, GTC

Crossfire, let us know how you shoot with that almost subsonic start velocity. We have had a raging debate here at the Fort about starting velicities. I'll be interested in your take on the situation.

SS

I had the...er, recieved is a better word, a DISTINCT impression from a Marlin Cowboy Gun sometime back, loaded with 510 gr PP marathon runners to about 1600 fps. First shot at 100 was a surgically placed 10X, follow---ons almost boring. Good word for those torpedos I think, that 'boring' word. They kinda bore right thru everthing. Used Matthews lube recipe on the paper patch, cheated and used Reloader 7 instead of black. ES was about 3, SD point something inscrutable. Easy...bird holes? Bullets that big don't make bugholes. Targets for the visually impaired. <img src="/ubbthreads/images/graemlins/grin.gif" alt="" /> Were a whole lotta fun that, the ache in my shoulder was gone in a few hours.

Very tough shoot today, In Tucson .....Long day ,4 relays, and everyone complaining 'bout visibility, and dust , midday a bit of dust devil action, and switchy head / tailwinds.

Match won with a 31, I'm pretty happy with my 25..........Opened on Rams, got 8, 2 lousy chickens, 9 pigs, and closing on almost invisible turkeys,.........6

More tomorrow, it's been a 15 hr day, 240mi round trip...time for a A beer, and bed.

GTC

Dan, that 510 at 1600 fps+, in harness with that crescent buttplate, and out of that relatively light rifle sounds pretty brutal.

I can honestly state that I've been belted way harder by A 350gr .45 cal at 2000+, out of a Marlin lever gun, than by a 540 gr .50 cal......in front of 109 gr 4831, out of my friend's Double .500 nitro-Express. ( Sorry, no idea as to that vel, we were busting rocks that day)

As Kenny Wasserberger projected, I also think Powder grade can have a lot to do with felt recoil. I watched the heavy charge ,3FG, high vel set shooting yesterday..........with 4 relays there was adequate time to spectate, and speculate. That sort of load really belts you.

I reckon that it's all about the RATE of bullet acceleration ,to a given velocity that makes it so.

In synch with Gunny's comments about softer alloys, I'm going to extrapolate that the harder alloys will kick you harder than the softer, and that's purely gut. While his annual consumption of alloy, powder and lube is hard to equal ( and enviable)....I nonetheless am blessed with the opportunity to shoot a lot, and that's where the "Gut" thing comes in.

One thing I observed yesterday, in watching the High vel group excercise , was frequent commment ....." Well the ELEVATIONS are great"..........but noticed that their wind correction call outs were frequent, and of fairly stout magnitude, given that the shifty wind conditions, and mirage changes were bad, they were subtle.

In counterpoint, I can state that once I was " Dialed in" for wind, that the only corrections made, on Pigs , and Turkeys, was minor elevations..................and that the groups were quite narrow...............taller than I would wish, but narrow ( (on " Invisible" , camoflage turkeys the elevations ran from high back, to high in the leg)..............we were short of spray paint, and the Three Points Silhouette range is ,at this time a pit of Caliche flour.............the targets, once recovered/ re-set come up out of this stuff a desert camo sorta shade....in afternoon light, and mirage ........HARD to get a good sight picture.

Sharpshooter, i guess what i'm scratchin around, and tryin' to get at here is that there's " No free lunch" and that one will either live with more wind sensitvity, with high vels, or a tendancy towards vertical stringing, at the lower end. We sure notice this at the 200m "Buffalo League shooot".........22LR,.............The match is typically won, with standard velocity target ammo, versus the High vel.......and there's definately a parrallel, of some sort .

I'd like to thank G&H270 for the tip on 50/50 Murphie's, and Isopropyl.................for WBS ( Wiping between shots)...it's slick, both literallly, and figuratively................interesting that the rifle swows a lot more "Torque effect", with this method VS blow tubing...........I'm havin to really conciously pull down on the forend now, or the thing will roll itself right up out of the notch..........and that shot will be a flyer.

Work safe, GTC

Crossfire, the Marlin CB had a fairly flat buttplate, not a joy for bench work but it really wasn't that bad for an 8 pounder, give or take. Suppose it would do 1800 fps with that bullet but the owner is not interested. Might strip of course, but being a Rigby owner I'd be curious.

I credit you a point on the soft lead/slow powder theory of recoil reduction. In a perfect world things would transform as appropriate, we mortals however have to make the choice and live with it.

The point about the standard velocity .22 RF winning the matches...'tis the cusp of my curiosity regarding the Matthews book. Other birds of the feather, Robert McCoy, Harold Vaughn too, they proclaim max drag at Mach 1, still pretty stiff in the transonic range where you fellas live and shoot. Mach .7-1.3 is the brunt of it. Lowers the BC, that being a chimera of sorts, subject to the whim of many things. Gets lower when slower, and when faster than... A boat tail VLD form at Mach 6 has a lower Cd than a Mach .5 Sharps bullet, or a .22 LR for that matter. 'Course it has to slow down too, sad to say. Understanding that drag as expressed in G's deceleration is still quite stiff in absolute terms, 'tis the coefficient that is lower. McCoy found an oddity of note, that being a 1" round ball in flight. It's Cd is weirdly low, very very low, and he attributed that phenom to a scale issue as relates to Reynolds Numbers.

Well, Jim Bridger never worried about all of that. I do enjoy the chat though.

Cross and Dan, I understand the problem we are all facing with sub/super sonic velocity and wind drift. I am beginning to suspect that there are some very non-linear things that MIGHT happen in these velocity ranges. To illustrate here are two ancedotes.

1) A very experienced Sharps guy had some trouble with hitting at ranges out to 250 yds with his Sharps. He spent some time shooting his rifle at all the ranges out to 250yds. This shooter found a couple of plateaus in his resulting drop chart. His take on it is that his bullet changed ballistic coefficients radically during its flight.

2) I was on my way to shooting my best silhouette score of a 31. I had hit 10 turkeys and 9 rams and on pigs was having some trouble when my spotter told me that he just watched one of my bullets TUMBLE and knock down a pig with a keyhole hit. Now that is a surprise with a load that is consistent enough at the turkey line to take 10 with solid hits.

Now granted these are ancedotal instances but I am beginning to be convinced that there are some very complicated things going on with these transonic bullets.

I dunno.

SS

Mike Rix...a shooter of established competency, and merit.......( overall high score at WCA 2002, and subsequent really consistant , and credible marksmanship)....

.....has, in his own words, " skinned and gutted" two chrony's, at 2, or 300 meters....chasing this so eloquently put..." Chimera"

Drive 'ya crazy....how well...........and conversely, how POORLY these rigs will shoot.

GTC

Sharpshooter, I entered unto a cataclymic debate with an ardent desciple of .17 bore DOGMA, that being in regards to the merits of bore size as relates to drift. "BC be all!", he sayeth. Well, yes and know... Yes, if you look at it from a theoretically pure perspective. Know, that is if you know, we fiddle in the real world, thus his point about a .17 Bore bullet with a BC of 1.05 is little but subjective theory. The thing that allows us to stabilize conical bullets, rifling, induces gyroscopic stability. It has real world limitations, and penalties as well. Given conventional technique of bullet construction, the BC he projected for that caliber is impossible. The debate left me in an odd position of "knowing" he was wrong but being unable to articulate the reason. Thus did I delve into the mystic world of exterior ballistics at some length. My wife was kind enough to slap me on occasion when I drooled in comatose trance. The things I speak of are what you characterise as "very complicated", far too complex for me to pontificate on here in the broad sweep. One item at a time, yes, of course. I know some things on the subject, certainly not all. Some of you sports know a lot more about the Black Science than I, perhaps we can learn from each other?

Your friends experience........BC changes constantly, never remaining constant despite the best wishes of the bullet marketers. While atmospherics are somewhat constant during the time of a bullets journey from here to there, its velocity is not, and that plays in a big way regarding BC. I do not know your buddy's methodology...I am left somewhat curious as to what he found and how...it is not terribly important as his experience is his, as were the bullet, gun and loads. Unique unto him. It is easy to attribute cause and effect to statistical backscatter, his testing range is very short. So short that most of the bullet flight would progress thru the Mach region of highest drag...not the place for plateaus necessarily. As it leaves the muzzle the bullet is backing into the region of highest drag from the get go, then slowing...slower, the farther is falls below Mach 1. Thus are Hindenbergs able to transit vast distances after that with little loss of velocity.

Your experience with the sideways bullets...it is not ordained that a slow heavy bullet MUST veer wildly from its intended course only because it is looking about along the way. Would not suggest that load for T-Rex in any case. The thing(s) that make a bullet tumble in flight are many, your specific thing, I dunno. An imponderable for me, a question asked of many, is this: YOU(non-specific, all encompassing) say the bullet tumbles due to turbulence as it slows thru the transonic realm. I say, show me. Where is it written that said zone is in fact turbulent. Where is the document, book, research paper, learned rocket scientist that can show me the light? I have searched far and wide, I have asked allegedly wisened practioners of the art...I draw blanks. So, I still do not KNOW this riddle, but I do know that bullet FORM influences this upset, so too does the Sg, or gyroscopic stability factor. I know too that many many years ago some yokel in the Army did some tests with an issue load in a .45-70, and plunked a bullet nose first into some sand at about 3500 yards. Aspect was about 75* if memory serves, but it was still pointy end first. The boys at one of the ballistic research labs in the desert Southwest didn't believe it possible, until they watched a virtual replay on their millimeter wave length radar. White Sands? Sandia?

Pardon my run on sentences, hope this didn't muddy the water for you too much. It is indeed a very surreal world, this mixing of lead and the speed of sound.

Dan, I read your post a couple of times and now that I have some narcotics and alcohol in my system I am feeling better. Bear in mind that the most operable part of my discussion was the "I dunno" part.

It could be that I misspoke when I said that the real mystery was the transonic part of the bullets flight. I was thinking transonic because that seemed to be the one place on the silhouette range where lots of us have had things go strange. The pig line at 220yds has tripped up many of us. Especially those that are launching bullets over 1250fps. It seems to me that the drop into the 1115fps range is around 200yds or so. Anyway, it just astounds me that the same load can shoot well enough to knock down 9 or 10 turkeys at 417 then 9 or 10 rams close to 560 can do such strange things at 220yds.

Here is my current thinking. The silhouette rifle I have been shooting does not do well past the turkey line if I let the starting velocity fall below 1200fps. Closing in on 1300fps is much better on turkeys and rams, but once in a while the same load will be wild at pigs. Of course, my solution was to shoot different loads at turkeys/rams as opposed to pigs.

Any insights you have are always appreciated.

SS

Sharpshooter, I am sincerely hoping the pain was transient but in the spirit of the Campfire applaud your efforts to keep your local distillery in the black, so to speak. <img src="/ubbthreads/images/graemlins/wink.gif" alt="" /> On occasion my prose is very convoluted.

I too suffer the dreaded "I dunnos", and the cursed "Horns of Delimma" as often or more so than many younger and wiser men. For that I am grateful. <img src="/ubbthreads/images/graemlins/smirk.gif" alt="" />

To the meat of it then: I do not think you misspoke, or if so, I misunderstood in the spirit of your statement I think. Without trying to sound superior, for I am not, I do not know what you know of the subject, thus I try to simplify/distill as I speak, the subject being as deep as the oceans. It is not necessary to understand how to calculate a 6DOF equation, it takes a super computer to do it in a reasonable amount of time in any case. Having an general understanding of what the calculation explains has some merit. Perhaps this is not the best example, my purpose only to make clear that being a math wizard(I'm not) does not preclude some understanding, and perhaps that leads to an epiphany when needed?

Recall that I mentioned the drag curve associated with the transonic range, that being the velocity of your bullets in the shorter ranges, and as you indicate your bullets are subsonic at 200 yards give or take. Differentiate drop from windage, Drop being a function of ToF, Drift being an issue of drag. If there is a question on this feel free to ask, I'm speaking in general terms, and again, I'm uncertain of your knowledge. The most severe effects of drift/drag are felt in the transonic realm...this may cause hit or miss issues if there is a breeze that day, even at shorter distances. Drag takes several forms, parasitic and induced, both in regions of laminar flow and turbulent flow in the flow field around the bullet. At the peak of the drag curve(mach 1) laminar flow wanes, and flow aft of that point is turbulent or detached, especially on the shank. This is a source of parasitic drag. The order reverses as speed increases or decreases from Mach 1. Look at the form of your bullet... at Mach 1 the point at which the radius of the bullet nose becomes caliber diameter, that is the point of differentiation in these two types of flow. As the velocity changes so too does the point of separation, moving aft as velocity increases or decreases. Having said that, understand that this in not just about your bullets, rather ALL bullets have this issue. Understand too that all bullets have laminar flow and turbulent flow simultaneously at any speed, regardless of form.

I don't want to muddy this but must address another issue at this point. Bullets go thru a lot of acrobatics when they leave a barrel. Assuming sufficient twist in the rifling, they are stabilized sufficiently to overcome the differential between Center of Gravity(usually aft), and Center of Pressure(forward). Gyroscopically stabilized forms may rotate rigid in space only when there are no forces to upset them, and when this occurs it manifests itself in the form of precession. Think childs top on the floor, wobbling when it is first set free, then again just before it falls. This is precession, and it is just what your bullets do. And my bullets too. There are many forces at play as a bullet exits the muzzle, and they all induce precession in a bullet. I will address two of them, those being of some import regarding the questions at hand. The first is imbalance about the axis of rotation. N'er was a bullet built that was perfect, only varying degrees of imperfection. Your bullet lumbers down the barrel, constrained to rotate on the design axis by the bore itself, even though slightly out of balance. When it leaves the barrel, it IMMEDIATELY begins to sort that out by shifting from rotation about the design axis to rotation about the axial CG. This induces a fast frequency precession in the bullet, and by the time it sorts this out the precession will null. Oddly enough this occurs typically between 100 and 200 yards, and is what is referred to as "going to sleep" in bullet speak. Well, there is another fly in the ointment, that being a slow frequency precession, and its magnitude is largely influenced by the Gyroscopic Stability Factor(Sg) imparted by the twist of your barrel. Many things contribute to this precession, gravity being but one small example, crosswind being another. It does not damp or null thru the flight of the bullet. It may diminish or grow larger as a function of Sg, but it WILL NOT null at any distance. The combination of these two precessions is best visualized by imagining that the bullet nose is marking a piece of paper, the resulting pattern being what is called a rosette, or continuing series of small loops about the larger circumference of nutation caused by the slow cycle precession. It is called an Epicyclic Precession. Because the bullet is wobbling in very small parts of a degree about the axis and is deflected by same, it causes the bullet to fly in fashion that resembles a helix about the line of flight. This INCREASES drag, something we already have enough of...and it is the source of Induced drag. Stick your arm out the car window at 60 mph, palm extended parallel to the tarmac. What you feel represents Parasitic drag. Rotate your wrist so that your palm is perpindicular to the wind, what you feel as an increase of drag is induced drag, even though both forms are coexisting.

In General terms an Sg of 1 is considered the theoretical point of stability vs. instability. From a practical standpoint, an Sg of 1.3 is a working minimum, and this value can change as a function of all the factors of atmospherics and bullet dynamics. Target shooters and especially lead shooters like twist rates as slow at possible, bullet deformation and stripping being two issues of consideration. Will a bullet unstable at 200 yards become stable at further distance? I dunno, but have doubts. Must take a moment to consider though that aerodynamic moments change dramatically(reduce) below Mach 1(thinking out loud about CG/CP issues) and thus Sg increases in such circumstance. Perhaps unstable(big wobble) but not tumbled may recover and proceed on its merry way? Once tumbled however, all is lost IMO.

I have rambled on way too long at this point, so will let you consider these things, ask questions if you care to do so. There is much I do not know about the specifics of your gun/load/bullet etc, thus it would be difficult for me to wax poetic about solutions. Better you figure this out as you can. Idle speculation... perhaps you use a bore rider, thus two points of separation betwixt laminar and turbulent flow...perhaps your twist is giving a marginal Sg for the transonic range...slumping???...probably not....bullet base deformation causing Tricyclic precessions? No, I didn't discuss that, better that I don't actually...confusing me on my best of days...

Regards

NICE post, well written, intruiging, I'll be savin' this one, to study, and further confuse myself..................thank's Dan.

GTC

Dan I'm with you part of the way. I understand the concepts of turbulent/laminar flow and Reynolds number in relation to fluid flow. Well that's from geothermal ground loop work. I am familiar with the precession rosette, sort of.

I am not really so interested in fixing a problem with my current silhouette rifle and load, which by the way I am changing as we speak. What I am interested in is the principles by which I should be trying to get the highest number of steel targets on the ground. Here is where I am now, see what you think.

1) Silhouette is really three distinct sports. Long range rams requiring enough energy to put them on the ground. Mid range accuracy on turkeys and pigs. Offhand shuetzen on chickens that for the most part is ingnored by us AAA and lower shooters in an effort to hit as many of the other three banks with bench weight rifles as possible.

2) The lightest recoiling caliber that will reliably put rams down is desirable. 40-65 probably rules, 45-70 is very popular and I think a fast twist 38 might be the best.

3) If I am going to shoot 4 or more chickens reliably, the rifle weight cannot exceed 10 1/2 lbs.

4) The ram load should have as high a velocity as possible to minimize wind drift and elevation problems. Of course accuracy must be maintained.

4a) The ram load at 1300fps can easily be a problem at the pig line for some reason I don't understand.

5) Silhouette is a statistical game. A rifle that shoots a load that drifts in the wind a few points less than everyone else's will eventually prevail in that fewer wind miss-calls will result in bullets in the dirt as opposed to catching the edge of the steel.

That's kind of where I am now. What do you think?

SS

Sharpshooter, by your leave I shall contemplate this a bit and return with my thoughts. I'm at the south end of three full days of fishing and pretending to be a bachelor...I'm whipped...

Either tonight or tomorrow AM, time for a siesta...

I with you Dan. I'm just recovering from the headache your first post gave me. I shall return soon from the fabled Fort Chadbourne silhouette match in a few days and I will bounce this off a couple of the better shooters there.

Take care,

SS

Sharpshooter, some of what you mention is I think extraneous to where I'm thinking the problem may be found. First thing I want to clarify is in your thought:



I understand your desire to have a flatter trajectory and less drift, but I'm thinking there may be some confusion regarding the relationship betwixt velocity and drift. Drift...isn't drift. It's a deflection. A popular but incorrect misnomer. Because it is a deflection the resulting displacement of a bullet is a function of DRAG.

D=W(T-Tv)

Where:
D= deflection in feet
W=wind speed in feet per second
T= Time of Flight at a specified distance
Tv=Time of Flight in a vacuum over same distance

It is a common misconception that bullets drift with the wind, they do not. You may do a little research and work some problems with a calculator, or go to any of several ballistics web sites and punch in a few numbers...follow the results. It is the nut of what I've discussed previously. Try this one if you like:
http://www.eskimo.com/~jbm/

The particular point I make is this. A given bullet similar to the designs you use, fired at velocities you indicate for your loads will suffer more displacement due to wind than the same bullet fired at subsonic velocities, even if just barely subsonic. If you do not know the BC or an approximation of same for the bullets you are using make one up, I'd suggest one in the .135 to .350 range. Typical of standard .22 LR bullets is a BC of .139 IIRC, and the number will serve for the exercise. A HIGH VELOCITY LONG RIFLE WILL SUFFER MORE "DRIFT" THAN ONE OF STANDARD VELOCITY. You might even find that published in some manufacturers ballistics tables. Your bullets will be likewise blessed.

Your 1250 fps load mentioned earlier leaves the muzzle at approx. Mach 1.08, right in the worst part of the drag curve. Lemme show ya something here.

[img][image]http://img.photobucket.com/albums/v298/muddler/dragcurve.jpg[/img][/image]

Now this is a fictional representation of a drag curve for a bullet of the sort you are shooting and the numbers are of my choosing and not necessarily representative of anything real, although the form of the curve is valid. The curve is also backwards from how they are usually depicted as tthe velocity is represented in the context of diminishing velocity, or as your bullet flys.

You bullet leaves the barrel in a realm of HIGH DRAG and probably within 35 yards or so has slowed to Mach 1, and even higher drag situation. Is is also the part of the bullets flight where the HIGHEST AERODYNAMIC MOMENTS are encountered, or in simple terms, that realm where your bullet is most likely to become the least stable IF the Sg is low, or marginal. As the bullet continues down range and slows further, the aerodynamic forces diminish, the Sg increases in relative terms and life is bliss...more or less.

My specific suggestions:

1. Shoot a shorter bullet if you think your twist rate is marginal.
Increasing velocity in an attempt to overcome a low twist rate is a fools errand...do some math, calculating RPM changes with a 100 fps velocity increase as compared to a 2" shorter twist, you'll understand my position I think.
2. Shoot at a lower initial velocity, say 1100 fps. It will reduce your flight time in the transonic velocity range, and your bullet will likely be more stable. I'm sorry that will affect your trajectory adversely, but your "drift" will be smaller as a result.

Dan, this is very good stuff here. I am following you so far. Let me give you some hard numbers to think about. I did some chrono testing on one of the hunting loads and I think I have some pretty accurate BC numbers. Initial velocity mean of 1254fps, 97 yards later the mean is 1152fps. I am guessing the BC on this bullet is around .385? That makes it drop below sound at around 135yds from the muzzle assuming the speed of sound at my elevation is around 1115fps. Do you still think there is less deflection to be had if the intial velocity is subsonic?

I am doing my best to square what I am seeing on the line with the numbers. Frankly, everyone I am seeing winning is shooting long bullets, fast. That means .40's weighing 425grs or so and .45's of at least 525grs. Most of the fellers that I watch win our matches month in and month out are shooting these bullets over 1200fps. Now this may simply be a result of some great shooters doing some dumb things, but I am not certain at this point.

Excellent discussion either way. I much appreciate your time and input.

Thanks,

SS

Yes. You don't have to slow down much to gain on this wind drift thing however. Some 'sperimentation would be useful on a day with a steady full value crosswind of perhaps 5-10 mph...old loads vs some new ones. New ones being slower and/or shorter in the bullet's perspective. If you still want the velocity try a bit shorter bullets. Reason we like longer heavier bullets is this:

BC = W/I x D^2

Where:
W = weight in pounds
I = Form
D = Diameter

Weight is the lead dog in this calculation, so with all of us being disciples of BC... in lead bullets, long=heavy=BC. BC is proportional to Section Density. The formula has been around a fair time, it is generally useful for ballpark discrimination but does not address atmospherics or phase of the moon. It is conceptually instructive however. Badda-da-boom.

Thank you for the kind words SS. I rather learn some things from this too, having not spent a great deal of time considering things in this realm. Most of my shooting is at higher velocities and with lead I am at shorter ranges, the application still hunting deer and sometimes hogs.

Your BC sounds reasonable to me. Take note that the speed of sound changes as a function of temperature. Faster on warm days, slower on cold. The difference in velocity between "fast" and "slow" in BPCR shootign is not really very much, measured in hundredths of a Mach. Without doing any figuring it may be that temperature differences have more influence on the issue than your muzzle velocity...significant if Sg is marginal. Going on memory alone(risky), I recall Harold Vaughn's words regarding twist rate and 6mm PPC competitors and their retentive ways...shooting 16" twists with 60ish grain bullets that stabilize fine in John Denver country, but not down here in the swamps where a 15" or maybe 14" twist is required. It is the influence of Aerodynamic moments as tempered by pressure altitude, temp and humidity. Perhaps we have more gnats in the air too....

Regards-

Ok Dan, sounds like an experiment is in order. I am thinking 200 meters alternating rounds with 20 each of my current 1250fps load and one throttled down to around 1120fps. There should be enough difference in elevation to distinguish which group the load falls into. If the breeze is halfway consistent I should get some decent results. T-test the results? I guess measure each round from a fixed point?

Good stuff here.

SS

SS, Not sure what "t-test" means.... based on your thoughts on BC and my assumptions....I wag'd 500 grains for the bullet, G1 form... expect a difference of drop at 200 yards in the range of 2-3". 1" less wind drift with the slower bullet, a 10 mph full value crosswind, ISA(International Standard Atmosphere). Rough figuring...maybe two different targets and common POA? Will be curious to hear your results.

Have you fiddled with the JBM calculator regarding your bullet design/length and twist?

Dan, I was thinking of a t-test to test for a significant difference between the deflections. See if I've got a real difference or random variance.

I am shooting a 40-70 Sharps straight with a 400gr bullet. Its about 1.24" long and has a .27 meplat. The reason I chose 200m is that I have a 4'x4' target board at that distance on my range. Frankly, the range can be anything out to 1200yds on my range, but I was ducking work.

You are right about two different aiming points on the same target board, I was going to alternate shots to minimize interference from other variables.

Suggestions appreciated.

SS