But with a smooth bore you lose the benefits of spin on the projectile you achieve through rifling.
You don't need ballistic tip subsonic. Actually flathead works the best or even better than that, hollow point in ballistics.Due to balance.
I would agree, spending time on a ballistics tip for Subsonic work is not something I would do.... Certainly all the drag programs don't show any advantage to them at airgun velocities.... For deer I would use a medium depth hollowpoint to get good expansion with fragmentation.... You can get that if the hollowpoint is too deep.... Bob
G1 is the "best" we have these days. For long-range G7 is better, but the numbers are smaller and bullets with a higher BC sell better (whether G1 or G7) so G1 is usually the one cited. And neither were intended to be accurate predictions at subsonic speeds. So just because the math says so doesn't mean that its the case. It goes against everything I know about aerodynamics that of these two bullets the hollowpoint has less aerodynamic drag. One is pushing a snow plow, the other is a dart.
If a guy happened to have a 18” barreled 12 gauge side lever top end laying around rusting . What valve configuration would you run ? Right now it has a .437 port going through the bolt . Maybe run a balanced valve and run it in the upper 3000’s to get the bullet / round ball moving ?
I would expect the two bullets you portrayed in Reply # 85 to have a significant difference in subsonic drag.... Comparing the upper one to an identical bullet with the plastic nose removed.... much less so.... If you made yet another design, with the caliber and LOA of the upper one, but a hollowpoint of about 50% of the caliber.... it could even have less drag.... Bob
It's not a matter of "logic", ballistics design is well known, and has been for decades.... Check out this Drag calculator, there is an explanation there of the program used.... http://www.geoffrey-kolbe.com/drag.htmThe "McDrag" program was developed by Robert McCoy at the Aberdeen Proving Grounds and tested against doppler radar and chronograph measurements, and is within 6% Subsonic (below Mach 0.8 ) and 11% Transonic (Mach 0.8-1.2) of real world results.... It is even better Supersonic (over Mach 1.2), at only a 3% margin of error.... Pointed bullets are vastly superior Supersonic, and the higher the velocity the narrower the angle of the conical nose shock wave.... so the narrower the nose must be to stay inside that cone (which at Mach 2 means within a 30 deg. angle).... Below Mach 1, and in particular below Mach 0.8 (900 fps) there are no shock waves to deal with, so a pointed nose makes little difference to the drag.... Elmer Keith was one of the first to demonstrate that, and his work with large Meplat bullets is legendary, particularly for pistol bullets, which for the most part are Subsonic.... A large Meplat (flat nose) transfers more of the energy of the impact to the quarry by making a larger diameter (but shallower) wound cavity, and hence is preferred for hunting, particularly with airguns, which traditionally are lower power than their PB counterparts.... There is a lot of similarity between our requirements and those of handgun (or blackpowder) hunters....Cutting the nose off of (shortening) a spire point bullet to get a Meplat is not the same thing as leaving the bullet the same LOA and using a larger Ogive radius to create a Meplat within that LOA.... The former does increase the Subsonic drag, the latter may in fact reduce it.... Experimenting with the Kolbe Drag Calculator will give you a better idea of what affects bullet drag and what doesn't than your eyeball.... That same drag program is also used by JBM Ballistics and Lila.... and other than using sophisticated CFD computer programs to analyze the drag, I have never found anything better....Bob
If you made yet another design, with the caliber and LOA of the upper one, but a hollowpoint of about 50% of the caliber.... it could even have less drag.... Bob
You don't need ballistic tip subsonic. Actually flathead works the best or even better than that, hollow point in ballistics.
HPs don't have higher drag,
worst case for this one is "89% correct"
In addition, nature seldom gets it wrong, and you don't see many birds or fish with flat skulls.... but on the other hand, not many of them fly/swim at Mach 0.8 either....
I wish you luck in your pursuit of a better ballistics approach.... I hope to do some real research in this regard once I get my LabRadar in 2 more years.... but until I have data to prove McCoy wrong, I won't be betting against him....
Try these dimensions in the Kolbe Calculator....Diam = 0.62"Length = 1.00"Nose Length = 0.50"Meplat = 0.00"Driving Band & Base = 0.62"Weight = 300 gr.You will get BC (M0.5) = 0.09 and BC (M1.0) = 0.06Now change the Meplat to 0.31" (50%) and leave everything else the same (including the weight, to keep the SD constant)….You will get BC (M0.5) = 0.09 and BC (M1.0) = 0.10 …. ie the same drag at Mach 0.5, but a lot less at Mach 1.... Want to see what happens between those two velocities?.... Look at the graph at the bottom of the page, at Mach 0.8.... Notice that the sudden increase in drag occurs at a HIGHER velocity for the bullet with a meplat…. Not only that, but the Drag Coefficient Cd is much less for the bullet with a Meplat, from that inflection point onwards.... peaking at only Cd=0.8 instead of Cd=1.1.... That is a lot more difference than 11%.... At Mach 0.8, the Cd of the pointed bullet is about 0.4, while that of the bullet with the Meplat is about 0.24 (40% less)…. At Mach 0.9, the pointed bullet Cd is about 0.6, while the one with the Meplat is about 0.35.... In the transonic region in particular, it seems that "eyeball logic" does not necessarily apply.... IMO, based on the extensive work of Robert McCoy, and verified by the Aberdeen Proving Grounds....Bob
There is no shoulder unless you select a Secant Ogive.... the default is a Tangent Ogive.... If you notice on the dimensions I gave you, when you run the calculator the ogive radius is larger on the design with the Meplat…. THAT is part of the reason it has less drag, the angle of the ogive where it meets the Meplat (where a shockwave would form) is shallower.... On both versions, the nose is 0.5" long, so the parallel portion of the bullet is also 0.5" long.... The ogive starts at exactly the same point on both....RE the warning about the nose drag, change the nose length to 0.65" to eliminate that.... The parallel portion will be shorter at 0.35".... You get the same 0.09 BCs at Mach 0.5, but a higher BC at Mach 1.0 in both cases (note the ogive is a larger radius with the longer nose).... The Cd graphs still show the same trends.... The bullet with Meplat has the start of the high drag transition at higher velocity, and the increase is shallower, and the Cd at Mach 1 is a lot less (0.45 vs 0.63)….I see no point in continuing to argue with you.... You have decided your eyeball is better than McCoy's math, and it very may well be.... My eyeball tells me the same thing.... However, my eyeball is not calibrated for Transonic flow.... Interestingly, the Subsonic drag is virtually the same regardless of nose shape, so below 900 fps they should in theory be equal within 6%.... I'll bet you that you can't measure a string of 10 bullets and get a Cd within 6%.... As with all theories, one you prove it wrong, it's time for a new theory.... I'm perfectly willing to throw out McCoy's work when that data becomes available.... Until then, I'll continue to use it as a useful design tool.... YMMV.... Just to give you something to think about.... which do you think might have less drag (same mass, so same SD)….the round nose pellet shown in red (Ogive 0.5 calibers).... or the black one with a 1.0 caliber Ogive radius and a Meplat…. I drew them different lengths for clarity, but you can assume they are the same LOA....I have been told there is no such stagnation zone when you examine such a design with CFD.... However, the velocity of the air in that area is closer to the velocity of the pellet than the free stream velocity in that CFD anaylsis…. so what is that, if not a stagnation zone (air being dragged along with the pellet)….Bob