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All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: rsterne on January 01, 2018, 03:15:11 PM
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I just received a PM asking some very good questions about why I chose flat-nosed designs for my BBTs rather than round-nose or spitzer.... and a follow up question about my opinion regarding .308 vs. .45 caliber for long range shooting with an airgun.... Here is my response....
Flat nose vs. round nose or spitzer.... I think this is a case of what your brain tells you (logic) not matching what actually happens in fluid dynamics.... All of the available "bullet design" programs I have run across, and those that calculate the BC, are based on the work of Robert McCoy who worked at the Aberdeen Proving Grounds and wrote several ballistics programs (in C++ I think), including McDrag and McGyro.... McDrag calculates the Cd (drag coefficient) and then compares that to the G1 drag model, to get the BC (G1) at all velocities from Mach 0.5 to Mach 5 in Mach 0.1 increments, with some extra calculations thrown in between Mach 0.8 and 1.0 where things change in a hurry.... McGyro calculates the gyroscopic stability over the same range, using the same bullet dimensions.... The required dimensions for each program are caliber, overall length, nose length, meplat diameter, nose radius (if not tangent), and base diameter and boattail length, if used.... This program is used on two websites, JBM, and Geoff Kolby's, and is also used by Lila in his drag/twist calculations.... JBM have it available for download (in C++ ? ) which I couldn't use, but I printed it out and then used all the equations and wrote my own Excel spreadsheet which faithfully duplicates all the calculations, and I used that to refine my Bob's Boattail designs.... I have both the original version, and a truncated version for airgun use that stops at Mach 1.5.... To get a feel for how this program works, try out Geoff Kolbe's site.... and JBM's Drag/Twist program....
http://www.geoffrey-kolbe.com/drag.htm (http://www.geoffrey-kolbe.com/drag.htm)
http://www.geoffrey-kolbe.com/barrel_twist.htm (http://www.geoffrey-kolbe.com/barrel_twist.htm)
http://www.jbmballistics.com/cgi-bin/jbmdrag-5.1.cgi (http://www.jbmballistics.com/cgi-bin/jbmdrag-5.1.cgi)
JBM's calculator artificially limits the Meplat diameter to 0.35 calibers (35%), that limit is NOT in McCoy's original program.... If you play with the calculators and change Meplat size, and concentrate on the high subsonic range, you will find that a bullet with a moderate Meplat actually has less drag than either a round nose or a spitzer.... In addition, there is no doubt that Meplats hit harder on game instead of just punching through, and they alloy the use of a Hollow Point without any drag penalty (only a slight reduction in BC because of the loss of mass).... Since MOST guys are not JUST paper punchers, and want the best possible performance on game, using a moderate Meplat makes sense, if it comes at no drag penalty, or actually with a slight drag reduction.... It is counterintuitive, but based on the best (only) ballistics programs we have access to, seemed to be the way to go....
One thing I found by playing around with the spreadsheet using McCoy's math, is that in the high Subsonic range (specifically Mach 0.85-0.95) and particularly right around Mach 0.9 (1000 fps) there is a slight reduction in drag available if you have the angle between the Ogive and the direction of flight around 20 deg.... I have never seen this published before, I believe it to be "original work" to come to this conclusion.... This means that shorter bullets, with shorter nose radius Ogives, need larger Meplats.... while longer, heavier bullets need smaller Mepats, to achieve minimum drag in that velocity range.... Below Mach 0.85, the Meplat size seems to make little difference.... but above Mach 0.95, and certainly above Mach 1 where a shockwave forms around the nose of the bullet then the Meplat needs to be smaller.... In fact at Mach 3 and above, the optimum seems to be a Meplat of only about 5% of the caliber (0.015" on a .30 cal).... which is likely why all the best long range bullets seem to have a tiny HP tip.... We get so used to looking at those shapes, and the hype about their incredibly low drag.... that our brains become nearly hardwired into thinking that spitzers must then LOGICALLY be best for airgun use as well.... McCoy's math certainly doesn't indicate that, and in comparisions to test data from the Aberdeen Proving Grounds, his McDrag program is supposed to be within 3% Supersonic (over Mach 1.2), 11% Transonic (Mach 0.8-1.2) and 6% Subsonic (below Mach 0.8 ).... The limitations of his program are clearly spelled out on the Kolbe Drag Calculator page.... Here is an example of the output of my spreadsheet using the McDrag math, for my 200 gr. .308 cal "Whiteout" bullet that won the EBR 200 yd. Big Bore in 2015....
(http://i378.photobucket.com/albums/oo221/rsterne/Ballistics/McDrag%20308%20BBT%20Whiteout_zpsiccbfznq.jpg) (http://s378.photobucket.com/user/rsterne/media/Ballistics/McDrag%20308%20BBT%20Whiteout_zpsiccbfznq.jpg.html)
That bullet was designed to take advantage of the extra power available from Helium, which they have since banned at the EBR.... Regarding the choice of .308 vs. .45 cal, I think that for airgun use, smaller is better, and here is why.... If you look at a cylinder of lead, the Sectional Density is proportional to the length.... The same thing applies to any given shape of bullet.... To get a higher SD, you need more length.... Consider this photo of a collection of bullet of nearly identical SD....
(http://i378.photobucket.com/albums/oo221/rsterne/Bullet%20Casting/Sectional%20Density_zpsmaptgb6x.jpg) (http://s378.photobucket.com/user/rsterne/media/Bullet%20Casting/Sectional%20Density_zpsmaptgb6x.jpg.html)
Note that the length is virtually unchanged from .22 cal to .45 cal.... I think it is pretty obvious which bullets have the lowest Form Factor (drag), it would have to be the smaller ones, right?.... You can calculate the Ballistics Coefficient of any bullet from the simple equation....
BC = SD / FF
where SD = Sectional Density (bigger is better) and FF = Form Factor (lower is better, the G1 model has an FF of 1.000).... Therefore, for bullets of the same SD, the lower the FF (drag) the higher the BC.... In the photo above, you would expect (other than for detail changes between designs) that the smaller calibers would have the higher BC.... OK, but larger calibers have higher SD's, doesn't that make up for it?.... Not in airguns, and here is why....
We have limited pressure available to accelerate our bullet.... We want to end up with a certain velocity range, and we can't realistically use barrels that are many feet long.... This puts an UPPER LIMIT ON SECTIONAL DENSITY that is related to pressure times barrel length.... Here is a graph showing that, if we want to reach about 950 fps....
(http://i378.photobucket.com/albums/oo221/rsterne/PCP%20Internal%20Ballistics/SecDensvsPresvsLength_zps152829e8.jpg) (http://s378.photobucket.com/user/rsterne/media/PCP%20Internal%20Ballistics/SecDensvsPresvsLength_zps152829e8.jpg.html)
Each line represents a different barrel length, so if, for example you select a 36" barrel and 3000 psi, the maximum SD you can drive to 950 fps is about 0.250.... In fact you will find these SD numbers are higher than you are likely to actually GET to 950 fps, you should consider them a "lofty goal".... What would these bullets look like in .308 can and .458 cal?.... Well, an SD of 0.250 in .308 cal would weigh 166 gr.... and in .458 cal it would weigh 367 gr.... I don't have any BBTs designed at those specific weights, but let's drop the SD down just a bit and compare a 334 gr. in .457 (SD = 0.227) to a 154 gr. in .308 (SD = 0.232).... and throw in a .257 cal of 112 gr. (SD = 0.242) for good measure.... Here are NOE's drawings, and their calculated BCs....
(http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Bobs%20Boattails/N.O.E._Bullet_Moulds_458-334-FN_BT_334_gr_Sketch_zpspgzjmbeq.jpg) (http://s378.photobucket.com/user/rsterne/media/NOE%20Bobs%20Boattails/N.O.E._Bullet_Moulds_458-334-FN_BT_334_gr_Sketch_zpspgzjmbeq.jpg.html)
(http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Bobs%20Boattails/N.O.E._Bullet_Moulds_308-154-FN_BT_155_gr_Sketch_zpsf4i3fzfc.jpg) (http://s378.photobucket.com/user/rsterne/media/NOE%20Bobs%20Boattails/N.O.E._Bullet_Moulds_308-154-FN_BT_155_gr_Sketch_zpsf4i3fzfc.jpg.html)
(http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Bobs%20Boattails/N.O.E._Bullet_Moulds_257-112-FN_BT_112_gr_Sketch_zpsopiwnovn.jpg) (http://s378.photobucket.com/user/rsterne/media/NOE%20Bobs%20Boattails/N.O.E._Bullet_Moulds_257-112-FN_BT_112_gr_Sketch_zpsopiwnovn.jpg.html)
Just visually, there is little question in my mind which bullet would have the best BC, and the best long range performance.... how about you?.... In an airgun, operating at 3000 psi with a 36" barrel, all three would end up getting about the same velocity.... THAT is why it is my opinion that smaller calibers are better for long range airgun use.... Now are there limits, YES.... Eventually at constant SD a small caliber bullet gets so long and skinny you can't make a barrel with a fast enough twist to stabilize it.... For the three bullets above, the optimum twist rate is 7" for the .257 cal, 11" for the .308 cal, but only 30" for the .458 cal.... A .172 cal bullet with an SD of 0.250 would have to weigh 52 gr., and need about a 4" twist rate.... but the BC would likely be over 0.40.... Alternately, if you have Helium available, you can reach the same velocity with a higher SD, which is why my "Whiteout" bullet was 200 gr., with an SD of 0.301.... You would need 3600 psi with a 36" barrel to even consider such a bullet shooting with air.... more likely about 4000 psi with that barrel....
As you increase the pressure (or barrel length), then you can increase the usable SD.... This is why people are having success with larger caliber PCPs, they require that combination of pressure and barrel length to allow them to use long, heavy bullets (with low FF's) in larger calibers.... and such guns are becoming more available.... Also, barrels with high enough twist rates to utilize such high SDs in the smaller calibers are harder to source.... That doesn't change the fact that ballistics favour the smaller calibers for airguns.... simply because of the limited power we have available.... There can be arguments made for why any individual caliber is "best".... but each argument will start with a premise regarding the combination of barrel length and pressure you choose to use.... Ultimately, that ends up back at the SD, which is the factor that governs the velocity you can reach with any given barrel length and pressure combination.... and the fact that for any given SD.... smaller calibers will tend to have a lower FF.... and hence a higher BC.... plus use less air and produce less recoil to obtain those results.... Again, practical limits, such as sourcing barrels and bullets will put a limit on your choices, however....
Bob
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What about the efficiency drop when we go towards small calibers? In pellet guns .177 usually gets less fpe per fill than .22.
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Don't know about sizes and sd or what not, we have a measured bc for the 20mm bt round 0.702 and it does fly pretty good for 170 gram chunk of lead.
Its not just about the caliber, you just need to make the bigger bullets well bigger and longer.
And what comes to distance and caliber choices, ask Carl what he thinks about the best caliber?
I'm with going bigger, but you need the gun that has the guts to deliver the velocity.
Easier to see what you hit when there's a big impact don't you think?
And no offense to anyone just my point of view.
Marko
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So Bob are you saying that a .357 flat nose bullet would be better than a diablo and also that a .357 is better than a .457 for say hog hunting at 50 yards? Thanks!
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Any bullet is better than a diablo!
Diablos have a terrible ballistics no matter what size.
Marko
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It is true that larger calibers tend to have better efficiency, but not by much.... From the same powerplant, they generally produce more total FPE because the larger caliber bullet has a greater area for the pressure to push on.... so although you get less velocity, you get more FPE.... because the barrel volume is larger.... Barrel volume and pressure are the major things that affect FPE....
That huge barrel volume of the 20mm (0.80" bore x 43" long) is the major reason for the huge FPE numbers.... At 300 bar, the theoretically maximum possible FPE is about 7800 FPE, but because of the mass of the gas, and many other factors, getting half that on air would be a HUGE accomplishment.... A 170 gr. bullet at 3100 FPE works out to about 730 fps.... The bullet has an SD of 0.585, which with a BC of 0.702 gives it a form factor of 0.83, about right for a boattail.... However impressive the energy is that bullet retains downrange, trajectory is much more influenced by velocity than BC, even at extreme range.... Using the chart in your thread in Reply #326, your drop at 1000 M will be 95.88 Mils (a Mil at 1000 M. is 1 M), so that is 3775".... The 112 gr. .257 cal bullet I show above, with a BC of just 0.396, at 900 fps, will only drop 2917" at 1100 yds. (slightly more than 1000 M).... Let's say the BC is way overestimated, and it's only 0.300.... Starting at 900 fps, it will still only drop 3126".... roughly 54 feet less than your 20 mm at 1100 yds..... Long range shooting requires BOTH velocity (for flat trajectory) and a high BC (for minimum wind drift).... The point of my post was that for any given combination of barrel length and pressure.... which governs the SD you can drive at a given velocity.... a smaller caliber bullet will have a higher BC for that SD.... and will require less air, and make less recoil doing it....
Carl loves large calibers because they kick up more dirt, which allows him to find the target easier at extreme ranges.... I won't argue the merit of that assessment....
Hunting is a totally different game than shooting at targets, it is mostly a game of delivering the appropriate ENERGY for the size of your quarry at the intended range.... Obviously, a .45 cal can deliver more energy than a .35 cal, from the same barrel length and pressure.... How much you NEED for your chosen game depends on what it is.... For a Ground Squirrel, or a Prairie Dog.... or even a Coyote.... I doubt you need the power of a .45, even a .35 cal.... Something in the .25 - .30 cal range might be a better choice.... For an angry big Hog.... MO POWER can't be argued with....
Bob
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Thanks Bob! Some of the hogs I've seen on the trail cams are pushing 300lbs plus, but don't really want them for table fair. I prefer the smaller ones. Just trying to learn more about big bores and their ammo and always appreciate your insight.
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Very impressive work Bob!
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I was more trying to figure out if there's a practical minimum caliber where the air as a propellant medium starts to get strangled. We now have .172 build for bullets and people are talking about even smaller calibers, is there a point where air is no longer practical for powering up small bullets? Casting those tiny bullets is then another thing but I guess we don't have to cover that in this discussion.
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Nice comparison Bob, and while bringing the 20mm up to the conversation as a reference for a bullet shape I was meaning to point out that a equally shaped bullet in bigger caliber would be beneficial over the smaller ones.
Something like 400-500gr out of a .457 at 900fps would be my choice.
Marko
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I agree 100%, Marko.... IF you have the power to push it.... Your bullet scaled down to .457 would be 489 gr.... the SD would be 0.334.... It would take about 4000 psi in a 36" barrel to hit 900 fps and develop 880 FPE.... A great combination.... but what a monster....
Bob
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Yes that it is Bob, and not too fun to shoot all day long. But no pain no gain right.
Anyway, we have the platform to do it infact you guys have it even easier. You just need to have Doug to make you a texan valve like Carl has.
This year there will be more truly high powerd pcp out I'm sure of that. Not by the big brand names but from the small shops around the globe. We have the valves to deliver very high flow with minimal hammer strike, all it takes is to build the frame around one of those valves.
Marko
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This year there will be more truly high powerd pcp out I'm sure of that. Not by the big brand names but from the small shops around the globe. We have the valves to deliver very high flow with minimal hammer strike, all it takes is to build the frame around one of those valves.
Marko
Totally agree with you Marko.
Very nice treatise on the subject Bob. 8)
Al
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rkr, you asked about the practical "minimum caliber", and considering that the air molecules themselves are pretty tiny, I don't think the physics of the airflow are the limiting factor.... You mention the difficulty of making very long tiny bullets, and THAT certainly offers a practical, and perhaps limiting, challenge.... If we look at trying to get the same SD as the three bullets in my first post (say about 0.24) in .172 cal, what would that look like?.... Well, it would be about 50 gr., and carrying the BBT idea to it's extreme conclusion, you would have something like this....
(http://i378.photobucket.com/albums/oo221/rsterne/Bullet%20Casting/172%20cal%2050%20gr%20BBT_zpsjrzsp2t2.png) (http://s378.photobucket.com/user/rsterne/media/Bullet%20Casting/172%20cal%2050%20gr%20BBT_zpsjrzsp2t2.png.html) (image obtained using the Kolbe Drag-Twist Calculator)
That calculator gives a subsonic BC (G1) of about 0.43.... but specifies a twist rate of 3.5".... The bullet is just over 1" long, so that is one revolution in less than 3.5 bullet lengths.... At 970 fps, it would be turning 200,000 RPM.... :o ....This, in itself, probably makes this an impractical combination for a bullet in a PCP with a 36" barrel at 3000 psi (our original criteria for the other 3 bullets).... If we shortened the barrel to 24", which would drop the maximum SD to about 0.17 (to get 950 fps).... that would drop the weight down to 35 gr.... and the bullet would look similar to the 112 gr. .257 cal drawing in the first post.... certainly a lot easier to cast.... It would still need a twist rate of about 5", which would require a custom barrel.... but it starts getting back into the realm of the possible....
Extrapolating this idea, there is, indeed, a minimum PRACTICAL caliber for PCPs, depending on the product of barrel length and pressure.... For instance, with Marko's 20 mm Monster, there would be little point in trying to build a .308 cal on that platform.... The gun, with it's 43" barrel running 300 bar, should be capable of pushing a bullet with an SD of 0.40 at about 950 fps on air (let's forget about Helium for now).... That would be a bullet weight of 266 gr. in .308 cal. (never heard of one).... or 394 gr. in .375 cal. (heavier than even the heaviest .375 H&H Magnum bullets)... but "only" 585 gr. in .457 cal.... You can "almost" get bullets that heavy in .457 cal.... If you jump up to .50 cal, then a bullet with an SD of 0.40 would weigh 728 gr.... NOW we're talking, you can get excellent long range bullets in that caliber for the .50 BMG.... even cast ones.... So for a gun like Marko's, a PRACTICAL minimum caliber might be .50 cal.... and with the ability to get much higher velocities and therefore a flatter trajectory, it should be much better for long range work.... I know it's jacketed, but for example a 750 gr. Barnes TAC-X Boattail has a BC (G1) of 0.766, and at 950 fps the drop at 1100 yards would be "only" 2384" (55 Mils).... compared to the 3775" (96 Mils) of the 20 mm bullet.... So, as you can see, the same idea holds true, smaller is better.... but with the proviso that there is, indeed, a PRACTICAL lower caliber limit that depends on barrel length and pressure....
Bob
PS. Marko.... Please realize I'm not picking on you, but it is helpful to have a gun so far "out of the norm" to use as an example.... to show that the same principles still apply, even in extreme cases.... I am still in complete AWE of your accomplishments.... 8)
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No worries there Bob,
But that .50 cal info gives me some ideas... ;)
Marko
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I thought it might.... 8)
Thinking about the idea of a minimum PRACTICAL caliber, I wondered how I could best convey that information.... Well, it relates to the maximum SD you can use to have any expectation of hitting 950 fps on air, which is in the chart I presented in the first post.... That, of course, is dictated by barrel length and pressure.... I have done quite a bit of looking at bullet designs, and VERY few are more than 4 calibers long (like my 112 gr. .257 cal in the first post).... If we make that assumption, and allow for flat-based bullets (which are a bit heavier than a boattail of the same length), we can calculate the approximate weight of a bullet that is 4 cals. long and then the SD of that bullet.... and they both relate to the caliber, like this....
(http://i378.photobucket.com/albums/oo221/rsterne/PCP%20Internal%20Ballistics/Weight%20and%20SD%20vs%20Caliber_zps8sl8c1q9.jpg) (http://s378.photobucket.com/user/rsterne/media/PCP%20Internal%20Ballistics/Weight%20and%20SD%20vs%20Caliber_zps8sl8c1q9.jpg.html)
Bullet weight is in red (left axis), and the SD is in blue (right axis).... The upper chart is for .177 to .357 cal, and the lower one for .357 cal to .80 cal (20 mm).... You can use these, in conjunction with the SD chart in the first post (shown below for convenience)....
(http://i378.photobucket.com/albums/oo221/rsterne/PCP%20Internal%20Ballistics/SecDensvsPresvsLength_zps152829e8.jpg) (http://s378.photobucket.com/user/rsterne/media/PCP%20Internal%20Ballistics/SecDensvsPresvsLength_zps152829e8.jpg.html)
We will assume you want the heaviest bullet you can have any hope of driving at 950 fps, to get the best possible combination of flat trajectory and BC (from the heavy SD), so you use the SD chart first.... Let's say you have a PCP with a 30" barrel running 4000 psi.... The maximum SD you should consider would be about 0.28.... So, you look at the right axis on the upper chart, find 0.28, and the slide to the left to the blue SD line (there just happens to be a dot there).... Go straight down to the X-axis (caliber), and it says 0.250".... Any bullet of a caliber smaller than that, you would expect to be greater than 4 calibers long.... which is going to be hard to stabilize (requiring a very fast twist), and more difficult to cast.... This puts an effective lower limit on the caliber for that combination of barrel length and pressure.... If you look at where the red (weight) line crosses the vertical line at .250 caliber, you will see that the weight is about 125 gr.... indeed a VERY heavy bullet for that caliber.... Therefore, for a PCP with a 30" barrel running 4000 psi, I would recommend that you look only at .257 cal and above.... 8)
You can do the same thing with any other combination of barrel length and pressure.... First find the maximum SD (for 950 fps), and then use the other chart to find the minimum practical caliber for that SD.... Interestingly, if you decide that you want some other SD (either lower or higher than recommended as a maximum on the first chart).... you can still use the other charts to determine the minimum bore size and bullet weight at that caliber.... Pretty neat way of looking at it, I think.... ;D
Bob
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This is a slight tangent and question on the max velocity and rotation speed that cast lead bullets can handle. What I am getting at there must be a point where the velocity and rotational forces are too great for lead to handle.
I don't remember the details so I'm going to generalize. So please excuse me. I remember reading that if you shot a powder burner bullet (copper jacketed) too fast and in too fast a twist it would disintegrate from the rotational stresses. I also remember reading that firing lead bullets too fast the lead would be stripped away by the lands because the lead didn't have the strength to stay together.
The only speed limit I remember is that the powder would melt the lead bullet base at a certain power level.
I know you can make lead harder but then it may be harder to engrave rifling thus reducing velocity or allowing blow by.
Has anyone confirmed a velocity and rpm limit for cast lead bullets?
Thanks,
Taso
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No idea.... but it would depend on the relationship between RPM and caliber.... 200,000 RPM on a .50 cal would have twice the centrifugal force at the surface of the bullet than on a .25 cal.... However, the force increases by the square of the RPM, so at 100,000 RPM the force would only be 1/4 as great....
Since for bullets of identical shape and proportions, the twist rate in inches required for stability is proportional to the caliber.... if the .50 cal bullet needed a 20" twist, then a scaled down .25 cal bullet would need a 10" twist.... Since we are generally aiming at about 950 fps, regardless of caliber, then the smaller bullet would be spinning twice as fast (4 times the force) but it has only half the radius (1/2 the force).... so the net centrifugal force at the surface of the bullet would be twice as great for the smaller caliber....
This means that smaller calibers are more likely to have a problem with coming apart if driven at high velocity in a fast twist barrel than their larger counterparts.... The point at which that would occur (combination of fast twist and high velocity) is something beyond my ability to calculate, however.... I can give you an example of what DOES work however.... My Hayabusa .257 shoots a 100 gr. bullet at about 950 fps, and it has a 7" twist.... The bullet is therefore spinning at nearly 100,000 rpm.... and I can tell you for a fact that they do NOT come apart.... Nor did the .308 cal 200 gr. "Whiteout" that was used in the 2015 EBR, even at 1050 fps in a 8" twist.... That is 94,500 RPM with a 20% larger bullet than my Hayabusa, so the equivalent of 103,500 RPM in the .257 cal.... To get the equivalent force in a .224 cal would require 110,800 RPM (about a 6.5" twist at 1000 fps).... and in a .172 cal it is the equivalent of 126,500 rpm (about a 5.7" twist at 1000 fps).... If I had to guess, lead bullets of less than 4 calibers in length will not require a twist rate fast enough to make them come apart in flight at airgun velocities....
Leading should be more related to the forward velocity than the rotation.... The distance travelled by a point on the bullet as it travels down the bore, even in a fast twist barrel, is not hugely greater than the barrel length.... In a 6" twist, in a 24" barrel, the bullet would rotate 4 times.... If the barrel is a .22 cal (that might need that fast a twist for a long bullet), the circumference is 0.69" times 4 = 2.76".... Think about drawing a triangle that is 24" long and 2.76" high and then measuring the hypotenuse.... It would only be 24.16", so that would be the distance travelled by a point on the circumference of the bullet.... If the muzzle velocity was 950 fps.... the speed of the lead relative to the metal of the bore would be (24.16 / 24) x 950 = 956 fps.... a difference not worth mentioning....
Think about it this way.... The only bullets I have heard of coming apart are .224 cal pills driven at over 4000 fps.... from something like a 7" twist.... They are rotating at 400,000 RPM, which is 16 times the centrifugal force you get at 1000 fps and 100,000 RPM in an airgun.... They have a thin copper jacket, which has been scored by the rifling, with weak spots just looking for a force big enough to rip the jacket from the core.... Is it any wonder it happens?.... I don't know what the velocity limit is for lead.... either before it melts and leads the barrel.... or comes apart from spinning too fast.... but my gut feel is that airguns staying under 1000 fps aren't going to run into significant problems.... although the faster you shoot a lead bullet, the more often you have to clean your barrel, I'm told....
Bob
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Thank you Mr. Sterne! There was mention in the .17 HMaiR thread of shooting bullets at 1300 fps or faster. So I thought my question was more appropriate in this thread than that one.
I've been interested in a .17 caliber bullet shooter for a long time but have not had the time or means to get the project going. I've just bugged you a couple times for your recommendations so I appreciate your explanations immensely.
Thank you!
Taso
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Thank you Mr. Sterne! There was mention in the .17 HMaiR thread of shooting bullets at 1300 fps or faster. So I thought my question was more appropriate in this thread than that one.
I've been interested in a .17 caliber bullet shooter for a long time but have not had the time or means to get the project going. I've just bugged you a couple times for your recommendations so I appreciate your explanations immensely.
Thank you!
Taso
1300 FPS? WOW thats fast. I bet I could if I had some Helium......lol. But i have seen 1030 fps and 1020 fps often.
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Cedric,
You don't know how happy I was to see your thread. I've been thinking about a rifle like yours in .177 or under caliber to shoot in Illinois for a long time. ;D
The recent posts in your thread are guys speculating about shooting 1300 fps or faster. I knew lead had physical limitations but I didn't have any first hand knowledge.
Thanks,
Taso
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Ced, the 1300 fps comment was a "what if you used 15.5 gr bullets".... not someone who actually did it.... Supersonic is a waste of time (and air) in airguns, IMO....
Bob
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Well sabot and 600 gr bullet leaving the muzzle around 1600fps will stay supersonic for a long way. ;D
Marko
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Ced, the 1300 fps comment was a "what if you used 15.5 gr bullets".... not someone who actually did it.... Supersonic is a waste of time (and air) in airguns, IMO....
Bob
Bob,
Yeah, I didnt take it as someone actually did it. I thought it was a misquote on me saying ive gotten 1030 FPS. Like some1 misswrote 1030 for 1300 FPS. Thats all.
But i also promote the idea of people testing what they believe might work. So if someone want to build a 17 cal HMaiR or a 224 supersonic air blaster and push special slugs at supersonic, HEY, I say go for it cause ya never know till you DO IT!
The 172 HMaiR was built with BLIND knowledge because there was previously no information out there on the caliber in an airgun. So I thought to myself, "Why Not" and went with what I already knew about the 17 HMR. And so far, every aspect has worked. Even down to my newly HP'd slugs. THEY FRAGMENT and it was just a guess on the HP.
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Maybe so, Marko.... but they will have more wind drift than if you launch the same bullet at 900 fps.... IMO, gravity you can compensate for.... the wind is your enemy....
(http://i378.photobucket.com/albums/oo221/rsterne/Ballistics/Wind%20Drift%20G1%20200yd_zpsg3s09xbp.jpg) (http://s378.photobucket.com/user/rsterne/media/Ballistics/Wind%20Drift%20G1%20200yd_zpsg3s09xbp.jpg.html)
Even with a BC as high as 0.40, you have to get to over 2000 fps MV just to get back to the same wind drift you had at 900.... and the worse the BC, the faster you have to drive it to break even.... I know it's counterintuitive.... but that is how bad the drag is at and over Mach 1.... Another one, for some specific bullets, at longer range.... I think this was for 400 yards....
(http://i378.photobucket.com/albums/oo221/rsterne/Ballistics/Wind%20Drift%20vs%20Velocity_zpsaxlbda63.jpg) (http://s378.photobucket.com/user/rsterne/media/Ballistics/Wind%20Drift%20vs%20Velocity_zpsaxlbda63.jpg.html)
Check out the 168 gr. Sierra HPBT, even it has to be driven at a MV of 2300 fps for the wind drift to be as low as what it would be at 900 fps.... 1400-1600 fps is the worst muzzle velocity to use for wind drift....
Bob
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BOB, Your title is Choice for LONG RANGE?? You should have defined THAT? I imagine you consider 200 yds as long range? I got some flack over a year ago when I was getting my new barrels for then .257's and posted, that going to start testing at SHORT RANGE of 300-400 yds!! I followed that with I consider MEDIUM RANGE 500-600 yds and after that LONG RANGE... People scoffed. Well up to date shows Doug can easily, and others shooting his guns. At EBR 2017, several shooting AAA Arms, Tom Compton's guns easily hitting dingers to 550 yds. Cedric has guns and skills and video to 440 yds hitting cans. Up North Airgunner too........Anyway long range is certainly what the shooter thinks it is.
It makes not one IOTA of DIFFERENCE on CALIBER if shooting .257 -.457. After shooting to 1108 yds with .257 I plugged into the Hornady Balllistic Computer, the parameters I thought I could reach with a .457 Texan and bought one. Video to post soon and FIrst time out in AUGUST 2017, shooting beyond 600 yds, I set up on Benchrest Benches and shot 383 and 412 gr slugs at 1070 yds.......Same as .257 with 85 gr bullets. I have video to post another time shooting steel RAMS with LEE 455 gr from Texan and are quite good.......Point is, any caliber from .257 to .457 will travel 1000 yds reasonably well. I just ran ## for .357 and will do same. I was using Spitzers but wanted distance..Flat Point will do it too, but with more wind drag will need MORE MOA to get there......
My learned by experience opinion is FLAT NOSE or HP for hunting and any caliber will work. Decide what your hunting options will be and go from there ......Light caliber and slugs for light game and Heavy for big tough game......
At the start of your thread BOB, you post what you have repeatedly posted of all the tables and math. The work of others and your BIBLE, so to speak. As we have disagreed on before, a LOT IS THEORY and does not TRANSLATE TO WORKING WELL in the ACTUAL SHOOTING. I know, I have about +30 molds for .257 and 457.....
Your THEORY of BBT is just that, theory and the math of less drag works ON PAPER........With your tapered LONG BT it translates to NOSE HEAVY PROJECTILE, period. That LONG BBT .308 bullet you keep promoting was NOT A VERY ACCURATE BULLET. Yes it did win EBR but not because it was better bullet. I saw pictures of those targets and a score of 169 out of 200 was pathetic. 31 points dropped out of 200.Yes wind, but was told it mostly was from behind shooters and not crosswind and they considered not as bad as some told the story?.......Targets looked like a shotgun pattern. Besides it was BARELY STABLE even getting speed up with HELIUM. Targets exhibited signs of YAW, I was told this? You built and entire gun in .257 to shoot this bullet scaled down. After over a year and excuses and forum members including me wanted to see results of this bullet and the rifle specially built to shoot this bullet. Well it DIDN'T work and there are those of us knew on air it would not be better than what is available now. I think you posted a 3 shot group that was maybe 1.25" but the couple 5 shot groups were terrible that you posted, and those were the best of the tests. I also read on AirGun Guild a post of yours to some question where YOU STATED that you had NEVER shot a 1" group at 100 yds, and did mention Doug, Cedric and myself as persons who can do it fairly regularly. But yu are promoting DESIGNS for people to BUY???
So my big gripe is your promotions of designs, dozens of them UNTRIED/UNPROVEN, and people thinking it must be better and they spending hard earned $$ HOPING IT IS BETTER? And to this day I know of not a better bullet being made. BBT especially, as they are ALL NOSE HEAVY, making them not balanced well. Yes a certain gun that can't shoot well for shooter and he may do better but that will be an isolated case.......
I told you before on forum the FIASCO of the Hornady AMAX 50 bullet designed by ballistic engineers and was a FLOP, early 90's... The 50 Caliber Shooters Association match shooters suspected BT TO LONG. I was there during middle 90's. BT was .300" LONG. Hornady re-tooled, ballistic engineers shortened BT to .200" and is still the excellent round it was after re-tooling. You never responded to my comment then........So engineers in the business and factory tooling to make it, with this costly error, how can we believe a hobbyist has a better IDEA? Using a computer to make drawings and math works on paper, but DOES NOT TRANSLATE TO ACTUAL PROGRESS or better in the field.
You have stated you don't work for NOE. OK, but you entice AL to make a design and keep cajoling unsuspecting persons to sign up over and over for a design not ever made before or even proven it better than any GC or FB bullet design out there.
I do not have problems with TRYING NEW STUFF. My problem is your flooding this forum and AIRGUN GUILD with all your unproven drawings and getting NOE to make them and the uninitiated thinking these have to be the best thing going. I concede certain rifles MAY work better than what they have shot before and is fine.
I shot all my long range stuff these past 3 years and were either FB or GC I have said to you before and I repeat it here, You will not tell the difference with an airgun if the BT works as well as another bullet.........If the shooter or gun can not hit squat, a BT will not help......
Another thing I have told you but you repeat all the BC nonsense of computation. Yes it works with powder speeds. I have used several times a Chronograph at 2 locations simultaneously, and calculated BC. At our slow speeds it doesn't work well. Say slug is .35 BC. FINE. go to 200 yds from 100 zero, with a 383 gr moa is +20.5. Start on target is CLOSE. Jump to 550 yds, and need 125 moa, fire and LOW needing maybe 10 more moa to get hit on target. It progressively gets worse as the original BC IS WAY OFF for distance, where with powder rifles fired 2800 fps is right on........when I get to 1000 yds or more I need 30-40 moa of angle MORE to get on target.. So what I do anymore when first getting MOA to reach way out there, enter say 600 yds, speed and weight of slug, then instead of BC entered of original I THOUGHT BC of .35, I keep trial and error enter a lower number that will coincide with the MOA i needed to get crosshairs center target......Then when I go to extreme distances I use this number to get a lot closer on my raked area instead of hitting so low I can't see an impact. For .45 have heavy bullets from .4- a 500 gr spitzer over .5 by manufacturer. To give me the MOA needed for 1000 yds I use a bc of .225 and first hits are in my raked area and then adjust accordingly.........My .257, over 2 chrono's had one bullet calculate at .4 BC also. At long distance I used .195 and right on.........So the calculation of BC at the MOLD CO do NOT TRANSLATE at our slow and greatly SLOWING speeds. If shooting close range, say 200 yds it won't be right on but practicing will show what come up you will need.......
I am surprised the GTA mods let you continually promote YOUR BBT designs, and promoting sales for NOE for UNPROVEN DESIGNS and persons possibly wasting their $$$. Now if there was a bullet BETTER, everyone would be singing the praises, including me....And better, I don't mean someone who claims ONE HOLE and shooting 40 yds. Amusing is that one hole is exactly THAT, first shot. All others make it bigger and if enough shots cut out paper, it isn't a one hole group.
I know you don't respond to my threads anymore as I always have something to say in disagreement you don't like, and am about the ONLY one who publicly posts a differing view on what you preach. I know you mean well but really have done no shooting that would PROVE YOUR IDEAS. I have shooting knowledge and your forte is making math theory add up on paper and graphs. Not quite the same thing........
Cheers..............Carl
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Carl, thank you for your constructive criticism.... If you had read through this thread, I refer to ballistics up to 1100 yards (1000 M), so you should consider that as part of my concept of "long range".... Although I did use drawings of BBTs to ILLUSTRATE the differences in shape between bullets of the same SD that were .458, .308, and .257 cal.... I did that only because I have them handy.... The same thing applies to FB bullets, or GC bullets....
Air can only push a certain SD to a certain velocity from a given barrel length and pressure.... I would think you would not dispute that.... Larger caliber bullets have a fatter shape for the same SD, and therefore a poorer FF.... This skews the BC in favour of smaller calibers.... Yes, there are limits, and I pointed that out as well....
If you think this is a advertisement for NOE, then I apologize, that was certainly NOT the intent.... The intent was to share how bullet shape is influenced by caliber choice.... and that the SD is influenced by your choice of barrel length and pressure.... That's it.... Period....
Bob
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No problem Bob..........The physics and math of your theories I admit are above my pay grade :o But do know what works in the field downrange, with air and powder rifles and do make it happen.......You keep writing, and I will keep shooting ::)
Carl
Carl, thank you for your constructive criticism.... If you had read through this thread, I refer to ballistics up to 1100 yards (1000 M), so you should consider that as part of my concept of "long range".... Although I did use drawings of BBTs to ILLUSTRATE the differences in shape between bullets of the same SD that were .458, .308, and .257 cal.... I did that only because I have them handy.... The same thing applies to FB bullets, or GC bullets....
Air can only push a certain SD to a certain velocity from a given barrel length and pressure.... I would think you would not dispute that.... Larger caliber bullets have a fatter shape for the same SD, and therefore a poorer FF.... This skews the BC in favour of smaller calibers.... Yes, there are limits, and I pointed that out as well....
If you think this is a advertisement for NOE, then I apologize, that was certainly NOT the intent.... The intent was to share how bullet shape is influenced by caliber choice.... and that the SD is influenced by your choice of barrel length and pressure.... That's it.... Period....
Bob
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There are a lot of good bullet designs out there. Cast and swagged, lead and non lead. I can only speak from personal experience and that is this. I shoot at roughly 120 yards and under with my air rifles, distance dictated by caliber and what game I am hunting. Ive shot less than moa at that distance out of 4 of my rifles, only my 308 Cothran has a non choked barrel. All with the bbt design. I’ve never needed more than one shot to drop what I’m after. That works for me. I also now am shooting some swagged with really good results. If I want to reach further my 7mm or 308 gets the nod. Short distance in a rural setting for pest or predator I use pellets, longer, on the farm or lease, I use bullets. Everything has its uses and place. Some guns-barrels shoot some bullets-pellets better-worse than others. If you find the one that works in your gun... use it. If it doesn’t .. find one that does. Half the fun is in the journey.
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I'm with Carl on this one, where are all the group pictures for the supposed superior boat tail bullets?
Can't remeber seen a single picture even of a decent group let alone one that was better than gascheck or plain base?
This is not just for you Bob, but for anyone who has shot BBTs POST SOME PICTURES PLEASE. Or any BT group pics.
Marko
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These pics are not BBT but they are boat tail pics. The group picture is from Steve Marsh who took second place at EBR with my boat tail bullet. He was shooting one of Doug's guns that Doug lent to him. The picture is 100 yards, 4 shots, the day before the competition.
I mainly shoot flat base bullets. I find boat tail bullets to be hard to shoot well and barrel picky. This .257 is the best shooting boat tail I have made so far and I have another caliber I ordered a special die to make a boat tail with.
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Nick, Those are Corbin REBATED BT and not quite same as BBT?
I Had the same Corbin Hydro Press you use and made them for 50 BMG and were good performing with powder.I won a WORLD CHAMPIONSHIP at 1000 yds making my own bullets in the REBATED BT design ........Yours I am sure are good for air power as BT isn't to long and the lessening of the weight at rear is balanced by the HP in the nose........Bottom line of any design, IS it accurate, and in a lot of barrels? With THE BBT's continually HYPED and nothing to prove it works well is my main complaint................Good luck with your products.........Carl
These pics are not BBT but they are boat tail pics. The group picture is from Steve Marsh who took second place at EBR with my boat tail bullet. He was shooting one of Doug's guns that Doug lent to him. The picture is 100 yards, 4 shots, the day before the competition.
I mainly shoot flat base bullets. I find boat tail bullets to be hard to shoot well and barrel picky. This .257 is the best shooting boat tail I have made so far and I have another caliber I ordered a special die to make a boat tail with.
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And in other way.... This is my humble opinion..Have quite a lots of molds well over 100...And on quanitys been casted well quite alot...And getting some data fellows who I've been casted. Been noticed that You can't predict which is better GC or PB bullets. I Know slightest off topic but concerning bullets still... And those diagrams and other is well over my league so I'm not gonna comment on those...
Here is one group shot by me. Bullet is BBT .30 - 135 grain.@ 100M Shot by Beaumont. It was my first time when I shot on that gun. Sadly there is nothing to compare to measurements.. 3 flyers.. or lack of skil to shoot that gun. This one could get tighter when if guns owner shoot that bullet... I think those which are in group are something like 40-50mm @ 100M Just quess can't remember.. I think this is my only data for BBT's
(http://i11.aijaa.com/m/00527/14506206.jpg) (http://aijaa.com/TnqzRT)
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Carl I agree but Marko asked for any BT pics so I provided the ones I had on hand. I am still working on the BT quest and I spent a lot of money on molds that don't work or work well enough. I am happy with flat base bullets, I think they shoot great in many guns and I try to sell slugs that work in the most guns as possible.
I also listen to the customers who ask for BT bullets so I try to satisfy the customer base and what they want to buy. If the right bullet design developes I am all over it but so far the this is the only larger caliber BT that has worked for me at this level.
This is not just for you Bob, but for anyone who has shot BBTs POST SOME PICTURES PLEASE. Or any BT group pics.
Marko
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Yeah Nick is right, I did ask about any BTs, but specially for bbt, thanks Teemu, I totally forgot that test that it was with bbt.
Thanks Nick, I was kind of hoping to see one of your bullets in for a comparison.
The main point was, superiority of the boat tail as it is hyped, and I want to see pictures of that.
I know I'm not going to see many longer range groups than 100m or yds. But it's over longer distance where the BT should rule over the conventional types. Longer ranges anyone?
Sorry for high jacking your thread Bob.
Marko
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thanks Teemu, I totally forgot that test that it was with bbt.
Marko
That was poor test...Just picking 10 bullets and shoot it on bad support. And my first time with that gun. I called that luck ;D Wierd thing on this matter is... Both fellows who own's those Beaumont's never asked to test that bullet by self :o Well not my problem. But it could be good...If first timer gets even that group. Yeah sorry for off topic
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I for one liked this thread. The treatise on SD and limited air power for caliber selection was educational and eye opening. Personally it's making me rethink .357 in favor of .308. It's a rare and wonderful thing when a thread can be so well thought out and educational. The drag function links provided appreciated.
With the GK Drag Function a person can mock up a bullet to find center of gravity. That's a handy tool as working that out on paper is time consuming. Math and the age of reason is a wonderful thing. For those on some sort of witch hunt you should watch Monty Python's satire The Holy Grail. Exclaiming "she turned me into a newt!" will never overturn the science of her weighing less than a duck to prove it.
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Ace precision .25 ..1/18 twist.. 100 yards. 950 ish fps, 51 grain, three in the top hole. Retained energy, 80 ft lbs at the target. Stock gun.. I think this bullet was designed for 1/16??
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I'm not quite sure where this thread went off the rails (well I am, thank you Carl).... but it has turned from an informative thread about caliber choice into a "lets bash Bob's Boattails" thread.... Since that is the case, here are a few FACTS....
I started the idea of using boattails for airguns because they have a PROVEN aerodynamic drag reduction over flat based bullets.... I originally (as most do) thought that their primary advantage was in the high Supersonic, but in fact boattails reduce the drag by a higher percentage Subsonic and Transonic than Supersonic.... There are lots of examples of drag calculators, based on hard science and testing, that can give you some idea of the possible drag reduction, and consequently lower susceptibility to a crosswind (their primary advantage).... I cite as an example the Lapua 200 gr. Subsonic 7.62 (.308) bullet, which uses a rebated boattail design.... When doing my initial research, I used a lot of the dimensions from the Corbin website as goals.... http://www.corbins.com/specs.htm#rbt (http://www.corbins.com/specs.htm#rbt) .... Carl has mistakenly said that my BBTs use a longer boattail than most, but in fact almost all my boattail designs are SHORTER than Corbin.... A quick look at the .257 cal 112 gr. drawing in the first post, and the dimensions listed by Corbin will tell the "tail".... I can only approach such a long, thin boattail as Corbin use with my longest, heaviest BBT designs, and in fact only 2 have ever been made that approach the Corbin dimensions, the 200 gr. .308 cal Whiteout, and the .257 cal 112 gr..... ALL of the other BBT designs that have been made so far have SHORTER boattails.... This is mostly from necessity, because you need enough length for the nose Ogive and the mid-body (bearing length).... so long boattails like Corbin use are impractical for most airgun use.... This is particularly true in the larger calibers, where a very long bullet would have a SD too high to reach any reasonable velocity to be considered for long range use.... In fact, when I am approached to design a relative light, large caliber BBT, I refuse, because there is simply not enough available length for a boattail.... For the explanation of the relationship between SD (weight and length) and caliber, to barrel length and pressure, I refer you to the first post in this thread....
I have NEVER made any accuracy claims for my bullets, and the reason is simple.... I do not currently have the time (I run a Motel during "shooting" season) or resources (read that as a zillion different airguns) to do the required testing.... Any experienced airgunner knows full well that some bullets work in some guns, and some do not.... This is no different than chasing down the ideal pellet.... Rather than keep my ideas and designs to myself, I have published them freely for ANYONE to try out.... Anyone that can read can find out why boattails have lower drag.... I use the same REBATED BOATTAIL design used by Corbin and Lapua because what has been written about it makes sense.... Here are two of the best articles about that feature....
http://www.corbins.com/rbt.htm (http://www.corbins.com/rbt.htm) .... http://www.swage.com/ftp/rbt.pdf (http://www.swage.com/ftp/rbt.pdf)
You will note that my ideas and designs lean heavily on the data and articles by Corbin, something I freely admit.... Why reinvent the wheel, when a perfectly good working one can move your wagon efficiently.... I did have one additional reason for choosing the rebated boattail design.... In the limited casting I have done, I have noticed that Flat Base bullets tend to have distorted bases from the shearing action of the Sprue Plate.... Gas Check designs have less of this problem.... In addition, with a Gas Check or Rebated Boattail design, the last part to leave contact with the crown at the muzzle is a moulded band, not one that could be damaged by cutting the Sprue.... Makes sense to me that if people spend a lot of time making sure their crown is perfect, why would they want to use a bullet where the last part to contact that crown is wonky.... IMO, you can think of a Gas Check Design (without the GC) as a very mild version of a Rebated Boattail.... and a lot of people swear by them....
I do agree with one thing that Carl said (backed up by Nck's experience).... and that is that using a Hollowpoint to move the Centre of Gravity back is probably a good idea.... That is exactly why I try and encourage the use of HPs.... As far as my involvement with NOE is concerned, after the Whiteout won the EBR, Al Nelson at NOE approached me about getting some of my BBT designs to add to their line of moulds.... He wanted to get into the airgun market, and liked what he saw.... I spent several months designing just about every conceivable weight of BBT for all the common airgun calibers, and those PB calibers commonly used by airgunners.... This runs to over 40 designs.... most of which are indeed simply scaled up or down for the different calibers, but they still needed tweaking, drawing, and dimensioning.... I asked for NOTHING in return, but instead took pride in the fact that Al valued my work enough to give airgunners the opportunity to try out some of the different designs.... The NOE business model for the BBTs is EXACTLY the same as for any other bullet design.... Somebody draws up a bullet, talks about it on the NOE Forum, and if enough guys think it is worth buying, they start up a Group Buy.... When 10 guys sign up, then the moulds are made, and put in the Store.... The guys that took the chance in the Group Buy to try an unproven bullet, get a 15% discount.... My designs are NO DIFFERENT than any others in that regard.... I suppose I could have told Al "no thanks, if you won't pay me I'm not interested".... but my designs are just as unproven as any others you would sign up for in a Group Buy.... so I gladly gave him the opportunity, no strings attached.... The benefit is that airgunners can try out new designs.... I'm sorry if some of you find that idea offensive or repugnant.... or think that when a new BBT goes to Group Buy I shouldn't let you all know about it.... but unless the Mods tell me I am stepping over the line, I plan to continue doing so....
In an ideal world, I would have a zillion different airguns, every make in every possible caliber, and have each design of BBT done up as a Custom Mould, shoot it in every possible gun, tabulate the results, and then only release the ones that work in enough guns to make them commercially viable.... You can bet that if I was doing that, I would expect to get paid for it, and not just a pittance, but big bucks.... I could also quietly go about all my modding of airguns and keep the information to myself.... in fact had I done that I would have wasted a lot less of my time posting, and nobody would ever have heard of Bob Sterne.... Instead, I try and share my ideas with all of you here, with ZERO compensation.... except the flack I get in threads like this.... It reminds me of a friend of mine who had a Laser sailboat he called "Flagellation".... because it felt so good when he stopped.... ::)
Bob
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Well, Bob it was not my intention to bash your desings, just that there has been so much hype about the advantages of the boat tail design, its superior ballistics but I have not seen any pictures of anyone actually shooting them.
So my post was about groups, I'm always interested about a potential bullet but always want to see how it does actually work.
Can you say there have been many pictures from BT groups around here, BBT or other or have I just managed to miss them all?
Marko
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There have been a few groups posted, some good, some bad.... some good ones right here in the last few posts, in fact.... Everyone has a different idea of what "accurate" is.... I have never achieved 1 MOA at 100 yards with ANY air rifle bullet OR pellet.... so for me, anything that can do that would be great.... I wouldn't care if it was pellet, FB, GC, or boattail.... I'd be tickled pink....
Carl, not so much.... he wants aspirin size groups at 100 yards.... I've never done that for 5 shots even with handloads in a .222 Rem.... ::)
None of this has ANYTHING to do with the purpose of this post, however.... If you want to start a thread about long range accuracy, why not DO that.... Even better, shoot the NUAH target, and qualify as a Master.... 8) .... There are currently only 9 guys on the GTA that have done that, and none of them at over 100 M.... https://www.gatewaytoairguns.org/GTA/index.php?topic=119449.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=119449.0) .... We have a spot just waiting for the first guy to do it at 300 yds....
Here are the rules for "Master".... https://www.gatewaytoairguns.org/GTA/index.php?topic=100865.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=100865.0) .... 5 shots in a 1 MOA group, and all inside or touching the 2 MOA ring.... 100 yard minimum, but same rules apply further out, if that isn't challenging enough... Maybe Carl can be the first NUAH Master at 1000 yards?.... only 5 shots allowed, though, all to score....
Bob
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Bob, just want to say thanks for all the sharing of information you do, and as the most voted for man on the GTA person of the year, I think you realize you are greatly appreciated. I think big bore threads tend to be the most testy ones on the GTA, seems like the bigger the bore the bigger the egos get! And perhaps rightfully so, a lot of big bore guys have something to be proud about. Anyway just wanted to say thanks, I am not a big bore guy but still find myself reading because it is always interesting reading your threads and trying to wrap my brain around them.
Thanks, and don't quit even if it would be less headache!
Enough said and I'm sure unnecessary, lol😊
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I'm not quite sure where this thread went off the rails (well I am, thank you Carl).... but it has turned from an informative thread about caliber choice into a "lets bash Bob's Boattails" thread....
Bob
Thanks BOB, You carefully forget I DID GIVE AN ANSWER to this threads TOPIC, 2nd paragraph, of my initial response on page 2. Stating that having shot .257 and .457 to OVER 1000 yds and UP NORTH AIRGUNNER doing same with a .357, it didn't matter what caliber was used. Shooter just needs to decide what SIZE was best for their needs....
YOU added the comment, and do it over and over about the EBR WINNING BULLET YOU DESIGNED, showing the drawings etc, as if it was something special. IT DID NOT place shots on target at that match better than an RCBS .308 standard bullet, and ONLY WON because another shooters ERROR resulted in a 20 point subtraction, and then he was in 3rd place by I believe 7 points. Bullet ONLY WAS STABLE BARELY on HELIUM. Yes it won but a better bullet, not hardly. AND NEVER shot in competition again.Then to prove it was a great bullet, you scaled DOWN that BBT to .257 and built a SPECIAL 7.5" twist rate barreled rifle to stabilize. How did that work out BOB???? Not very well.
You think I am bashing BBT........You keep bringing it up and posting that long 200+ gr .308, and after so many times hearing the EBR THING, I consider it bragging from your side I have heard it and seen it posted so many times. All I am doing is giving another point of view on that specific bullet to readers who are unaware or not heard another slant on that subject. And yes you brought it up in the initial post, so FAIR to have a view that doesn't agree with how good the bullet is or isn't, in this thread. YOU provided the ammunition, so to speak. Specifically that EBR LONG .308 and same design scaled to .257.
We have hashed this out before. But you keep implying it was such a great bullet, flack or dissenting opinions will flow from me. Bob if you design a bullet that is better consistently than any of my SAECO molds deliver in .45, or Arsenal in .257, I and others will be all over it....Until then
Also having an opinion and stating additional information you don't want to remember or hear, isn't bashing.......It is called a disagreement..........And in CIVIL DISCOURSE, allowable............
Cheers.........Carl
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you scaled DOWN that BBT to .257 and built a SPECIAL 7.5" twist rate barreled rifle to stabilize. How did that work out BOB???? Not very well.
The "not very well" is purely your opinion.... I posted a group back in the spring, during initial Chrony testing, and until I get the time to properly test the Monocoque (after the Motel closes in 2021) I may very well not get back to shooting it.... The large black square is 2", so that group, at 100 yards, is just a whisker over 1".... pretty much the best I have ever shot at 100 yards with any airgun.... first time out with that gun and bullet....
(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Monocoque%20100%20yd001_zpsikrnqru2.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Monocoque%20100%20yd001_zpsikrnqru2.jpg.html)
As far as the special 7.5" twist barrel, it was actually a 7" twist, which is what the calculations told me was the correct twist for a .257 cal bullet of that length with that boattail.... and the holes look perfectly round to me.... Compared to that target you keep posting with the aspirin sized group it's terrible.... Did you get that group the very first time out with that gun and bullet?.... Somehow I doubt it.... ::)
You keep doing what you do well, shooting at targets at long range, using big bullets that kick up a big cloud of dust so you can see the impacts better until you finally get on target.... It's entertaining, and shows how far a bullet from an airgun can carry.... Your accomplishments are legendary, just hitting anything at that distance is impressive.... I'll keep plugging along, trying to develop a bullet that is accurate enough that even you might try it.... while having the superior aerodynamics that only a boattail can provide, and the inherently lower wind drift that goes along with that.... I don't care how well I can shoot.... I'm just trying to help the sport improve to the best of my limited ability.... All the snipers in the world can't have it wrong....
Now can we get this thread back on topic, please?....
Bob
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you scaled DOWN that BBT to .257 and built a SPECIAL 7.5" twist rate barreled rifle to stabilize. How did that work out BOB???? Not very well.
The "not very well" is purely your opinion.... I posted a group back in the spring, during initial Chrony testing, and until I get the time to properly test the Monocoque (after the Motel closes in 2021) I may very well not get back to shooting it.... The large black square is 2", so that group, at 100 yards, is just a whisker over 1".... pretty much the best I have ever shot at 100 yards with any airgun.... first time out with that gun and bullet....
Bob
I remember you posting that......The 3 shots aren't bad, and you said it was best group and also posted a couple 5 shots, the best you said of 5 shot groups and weren't good, your admission. So the ones that weren't as good as the couple of 5 shot groups and not shown were even worse??
And yes with my rebuilt .257's, and 85 gr and 92 gr Arsenal molds, 5 shot groups were better than 1" first time out, and a lot were .5"...........I showed Aspirin comparisons just to show sometimes it all comes together and I consider 1 moa as very acceptable accuracy for airgun. Over counter powder rifle, stock same but custom and hand loads, even 1/2 moa to me is not acceptable, As you mentioned, accuracy means different things to different people........
I am done.................Carl
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Carl, would you mind posting your caliber, mold, muzzle velocity, and barrel twist rates that you have achieved what you would consider good accuracy with? It's been my suspicion that the subsonic stability factor models we have been using are close, but not quite right (just in the same way our drag models cannot quite predict accurate BC numbers for pellets). I am trying to compile a field experience vs calculated chart to compare theoretical s factor optimums vs what people are actually getting good groups with
Edit: I would also need your approximate elevation above sea level.
Also, thank you to both bob and Carl, for both innovating in your areas of passion. Remember, without disagreement there will no longer be innovation
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Good idea, Shane.... perhaps start a thread for that?.... Others may have input as well....
Bob
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Wow Bob. i actually kept up with that. Awesome explanation!
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Bob,
I purchased both the 155 gr. and 170 gr. .30 cal. NOE boattail bullets. I have had decent results with these moulds but have struggled with a persistent wobble or yaw which can be seen on target by oblong bullet holes. Most of my testing was at 300 yards. I have experimented with various alloys from pure lead to half linotype & half pure lead. I have also experimented with various sizing diameters. At first I thought the problem was that I didn't have a fast enough twist rate. I had a 1 in 10" twist rate at the time. So I went through the process and expense of having my 10" twist Shilen barrel removed and replaced it with a 1 in 7" inch twist match grade Shilen. Still the yaw on target was present with both bullets. It is worse with the longer 170 grainer. The best bullet that I have shot so far in my rifle is a RCBS 165 gr. Silhouette bullet that I had the gas check shank removed. My best groups occured with the 10" twist barrel and this modified RCBS flat base bullet. I will retire the NOE boattail bullets. In my rifle they just won't fly without a yaw. And I'm not going to go to the cost of putting an even faster 6" inch twist barrel on it. I will say that groups did improve on the 170 gr. boattail bullet going from a 1 in 10" twist to a 1 in 7" twist barrel. But neither boattail has been able to match the RCBS flat base bullet in the 10" twist barrel. Any new moulds that I purchase in the future will be flat base or have gas check shanks because for what ever reason, they are much easier to stabilize. Also, you'll never get the benefit of the theoretical B.C. advantage of the boattail bullets if they are cork screwing through the air. That's going to cause additional drag on the sides of the bullet. A equally weighted flat base spitzer bullet that flies true will probably have a better BC than a boattail spitzer that's yawing through the air. I do learn a lot from your post. And appreciate your mathmatical prowess. But what sounds good on paper doesn't necessairly work out in the real world. As far as what's the best caliber for long range I think that it's been proven that it really doesn't matter. What ever powerplant that you own that can drive a high BC bullet to 950 fps will work. The real differences in caliber are more a function of practicality. The smaller calibers use less air (that's an advantage) but make smaller holes and kick up less dust and are therefore more difficult to spot at long range (that's a disadvantage). And just the opposite holds true for the big bores which use a lot more air but make bigger holes and kick up more dust.
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Thanks for your efforts to help in understanding things, Bob.
Also thanks for being patient and answering questions in PM's.
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you'll never get the benefit of the theoretical B.C. advantage of the boattail bullets if they are cork screwing through the air. That's going to cause additional drag on the sides of the bullet. A equally weighted flat base spitzer bullet that flies true will probably have a better BC than a boattail spitzer that's yawing through the air.
I agree 100%.... and thanks for your detailed post of your experience with the BBT's.... I have not seen any yaw with my .257 cal 112 gr. in a 7" twist, but have not shot past 100 yards yet, so perhaps that will show up at longer range.... As far as the advantages of larger calibers at long range in punching bigger holes, delivering more energy, or kicking up bigger clouds of dirt on impact (so you can walk your shots onto the target).... I agree 100% on that as well.... However, the original concept of this post was to show the difference in the basic ballistics between calibers from an internal and external ballistics point of view.... Internally, the SD is limited by the barrel length and pressure.... Externally, for a given SD, smaller caliber bullets can have a better BC (this applies to FB or GC as well).... Until you hit the point where the bullet ends up too long to work properly because you either can't make it accurately enough, or get a fast enough twist to stabilze it.... or just plain need more FPE to dispense with your intended game.... IMO smaller calibers have the advantage at long range in airguns.... I just tried to show the reason behind that in this thread.... YMMV of course....
Bob
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you'll never get the benefit of the theoretical B.C. advantage of the boattail bullets if they are cork screwing through the air. That's going to cause additional drag on the sides of the bullet. A equally weighted flat base spitzer bullet that flies true will probably have a better BC than a boattail spitzer that's yawing through the air.
I agree 100%.... and thanks for your detailed post of your experience with the BBT's.... I have not seen any yaw with my .257 cal 112 gr. in a 7" twist, but have not shot past 100 yards yet, so perhaps that will show up at longer range....
Bob
I would like to point out that Cedric shot your BBT in 7mm out to a very accurate 205 yards, repeatedly hitting an apple at that distance, in his second 7mm Corsair video. I would call his shots MOA or better from what I saw.
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I shoot the .308 135gr BBT in my home made rifle. It has a 1-20" TJ barrel on it. Is it the most accurate rifle I don't think so. I would not hesitate to shoot a hog at 100yds with it or a coyote at 200yds. I can hit a 8x10 gong all day long at 200yds using shooting sticks no benchrest stuff. On paper I see no signs of yaw. I've tried several bullets that fellow GTA members sent me and different molds I have and so far the BBT is the best out of my rifle.
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Hmmm.. I should try that same bullet on Corsair. Also 1-20" TJ barrel... I've been thinking that it is too long bullet for that twist. Or not enough power to push it....
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I shoot the 78.6 and 95 grain Bbt out of my Cothran, very good to 100 yards which is as far as I shoot it. Also a tj 1-20 twist. I like the 308 for bigger stuff and have a .257 barrel for it. I find I’m leaning more to calibers 308 and down. Here in Alabama we can hunt deer with .30 and above, coyotes and hogs whatever will take them, so that opens up a lot of longer range calibers, the 224, .257, 7mm etc.