12ga Big Bore



Author Topic: 12ga Big Bore  (Read 2224 times))

Offline rkr

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Re: 12ga Big Bore
« Reply #80 on: February 03, 2019, 05:40:00 PM »
But with a smooth bore you lose the benefits of spin on the projectile you achieve through rifling.

There are "finned" slugs that are supposed to spin. I don't know if they work or not but perhaps worth investigation?
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Offline fpjeepy

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Re: 12ga Big Bore
« Reply #81 on: February 03, 2019, 07:39:27 PM »
Aluminum oxidizes into aluminum oxide. The stuff on sandpaper. Some people recommended against it for that reason. Alloys or coatings could help this. But I also don't think the aluminum bullets would be heavy enough. Or if they were heavy enough they would require so much twist to stabilize that it would drastically reduce muzzle velocity.

I think like Bob suggested tin could work well. Or Pewter (92/8 Tin/Antimony) They would be expensive, but drastically reduced labor, but being able to just pour them.

I had another couple crazy ideas, maybe #9 shot lead mixed into a strong plastic polymer. Again, it would be easy to pour. And if the mold was set vertically the bullet would have most of the weight forward.

Or maybe a Pewter "Power belt" The plastic skirt would help reduce barrel friction and provide a good seal. And a ballistic tip would improve BC, and a hidden hollowpoint behind it would help reduce the weight. For that matter maybe a traditional copper jacketed lead bullet could be made light enough. Since "Power belt" has all the tech figured out, maybe they would do a limited quantity run of a couple thousand 0.62 bullets. Worse come to worse they could be used as 20ga slugs. I'm confident they would work in a can, because that is what the suppressed maxim 50 recommends for their guns.
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Offline Kinetic45^

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Re: 12ga Big Bore
« Reply #82 on: February 03, 2019, 09:05:21 PM »
I was lucky enough to score a box of these:
https://www.midwayusa.com/product/173073/inceptor-preferred-hunting-bullets-458-socom-458-diameter-200-grain-arx-frangible-lead-free

I can't understand why the are discontinued, they shot GREAT in my Texan!!!

Metal dust infused polymer composite, did not foul the barrel in any way, accurate and good FPS/FPE
« Last Edit: February 03, 2019, 09:08:21 PM by Kinetic45^ »
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Offline TPL

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Re: 12ga Big Bore
« Reply #83 on: February 04, 2019, 04:09:10 PM »
You don't need ballistic tip subsonic. Actually flathead works the best or even better than that, hollow point in ballistics.

Due to balance.
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Offline rsterne

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Re: 12ga Big Bore
« Reply #84 on: February 04, 2019, 07:39:00 PM »
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
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Offline fpjeepy

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Re: 12ga Big Bore
« Reply #85 on: February 04, 2019, 10:58:45 PM »
You don't need ballistic tip subsonic. Actually flathead works the best or even better than that, hollow point in ballistics.

Due to balance.

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.

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Offline fpjeepy

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Re: 12ga Big Bore
« Reply #86 on: February 04, 2019, 11:07:28 PM »
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

I personally, wouldn't be looking for expansion. A 0.62" hole would be good enough. (by comparison, I would guess more than 70% of deer have been killed by a bullet smaller than .308 in diameter with less than 2x expansion. [0.618"]) And if the bullet were to expand to 2 times its diameter I suspect it would not have enough energy at 300gr to get a pass through.
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Offline Brian W Cook

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Re: 12ga Big Bore
« Reply #87 on: February 09, 2019, 08:05:24 PM »
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 ?
« Last Edit: February 09, 2019, 08:07:27 PM by Brian W Cook »
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Offline rsterne

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Re: 12ga Big Bore
« Reply #88 on: February 09, 2019, 10:52:40 PM »
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
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Offline TPL

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Re: 12ga Big Bore
« Reply #89 on: February 12, 2019, 02:09:29 PM »
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.
G1, G7 and whatsoever are only mathematical ballistic models we use to estimate bullet fly. BC is a relative number comparing actual bullet drag to its speed against any chosen mathematical model. The model we use is not changing the bullet behavior. It only changes numbers. There is no the best model for short and long range. Only for bullet shape vs. speed. You are bind to subsonic, right?

Bullet model mostly used for subsonic is G1. For supersonic it is mostly G7. That doesn't change bullet properties in any way. None of those models are telling exatcly about your actual bullet unless you make a new mathematical model, Gfpjeepy12GA.  :D

What comes to real drag you could try for example this: http://www.geoffrey-kolbe.com/drag.htm. It has found very good. Try with sharp nose vs. flat in subsonic area and see youreself. You'll see the difference also supersonic. Ballistics can surprise sometimes.

There is only one thing to remember with ballistic calculators, garbage in, garbage out. Oh, maybe two, not all of them are suitable for all uses.
« Last Edit: February 12, 2019, 03:26:09 PM by TPL »
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Offline MJP

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Re: 12ga Big Bore
« Reply #90 on: February 13, 2019, 09:36:58 AM »
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 ?

Full bore size porting, with as big of a valve you could possibly fit in your frame, and still have enough area to flow past it.
 Balenced of course, no point making it pain in the behind to cock it.

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Offline fpjeepy

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Re: 12ga Big Bore
« Reply #91 on: February 13, 2019, 01:44:13 PM »
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

Why do you say that? I don't follow the logic
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Offline rsterne

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Re: 12ga Big Bore
« Reply #92 on: February 13, 2019, 02:15:48 PM »
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.htm

The "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
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Offline fpjeepy

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Re: 12ga Big Bore
« Reply #93 on: February 18, 2019, 01:13:06 PM »

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.htm

The "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

I guess maybe I was a little confused. You said..

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

I took that as saying that a hollowpoint will have less drag than a pointed bullet. Which I believe is what TPL was saying.

You don't need ballistic tip subsonic. Actually flathead works the best or even better than that, hollow point in ballistics.


But what you describe above is making another bullet that has the same LOA with a flat point. This will make a heavier bullet and in turn a higher sectional density and in turn a theoretical lower drag. But in my opinion, that's not a fair comparison because higher sectional density bullets have a higher ballistic coefficient. Using the calculator I failed to ever make a bullet that had a higher B.C. with the same weight that was flat pointed vs the pointed at Mach 0.5 (They didn't list 0.8). And even at that, it is only guaranteed to be within 11% (for 0.8) which isn't great. I.e disregard if the gains are less than 12% . Hollowpoints will always be lighter than their parent flat point and therefore have higher drag. 

I would argue logic is important. I see no benefit in blindly following an 89% accurate formula. There is a reason rocketships, airplanes, and torpedos are pointed. If this wasn't true then I could be a millionaire by patenting the hollowpoint racing bike helmet, the hollow-tip airplane wing, and the flat-sided baseball.

I'm not arguing that flat pointed and hollowpoint don't have a place in airgun hunting. I think they are greatly suited for that. But not because they have less drag than their pointed counterpart. Rather, because they are great in terms of terminal ballistics.
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Offline rsterne

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Re: 12ga Big Bore
« Reply #94 on: February 18, 2019, 01:44:52 PM »
No, by varying the density (ie specifying a constant weight in the Kolbe Calculator, for instance your 300 gr. target), you can separate the effects of length and shape from that of the SD.... HPs don't have higher drag, they do, however have a lower SD, all other things being equal, and a different CG position....

I am not about to try and "guess" my way around a proven ballistics program by doing what I think looks right.... No program is perfect, and as you state, worst case for this one is "89% correct" (actually, at Mach 0.75, it is 94% correct, that 11% error is only between 900-1350 fps, being the least reliable at Mach 1).... 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....

Bob
« Last Edit: February 18, 2019, 01:51:06 PM by rsterne »
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Offline rsterne

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Re: 12ga Big Bore
« Reply #95 on: February 18, 2019, 02:15:44 PM »
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) = 0.06

Now 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....  :o

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

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Offline fpjeepy

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Re: 12ga Big Bore
« Reply #96 on: February 18, 2019, 02:37:24 PM »
HPs don't have higher drag,

You have nothing to prove this. The calculator was developed for flat pointed bullets.

worst case for this one is "89% correct"

Actually, from the link you provided... "This showed that the typical standard deviation errors to be expected were about [...] 11% in the transonic region.."

"Standard deviation errors" means 68.2% (one standard deviation) for the bullets they tested fell within 11% of the value calculated. So the worst case scenario would be worse. 

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....

How about airplanes? Maybe McCoy should call up Boeing and let them know what they are missing.

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....

I don't think you need any fancy equipment. Just buy some muzzleloader bullets, and pull the ballistic tips off half of them and show me that those shoot flatter at 950fps.

I did't intend for this to become a ^*%$#@ match... You keep shooting hollowpoints and I'll wrongly keep shooting ballistic tips and everyone will be happy.
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Offline fpjeepy

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Re: 12ga Big Bore
« Reply #97 on: February 18, 2019, 02:50:15 PM »
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) = 0.06

Now 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....  :o

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

I did that and I got this message... "Warning: Nose length is less than one calibre. The calculated nose drag contributions for transonic and supersonic speeds are probably too high."

i.e this is not based on the extensive work of Robert McCoy, and verified by the Aberdeen Proving Grounds....

Additionally, the program doesn't allow you to lock the secant location. So all things are not the same. The area near the shoulder (the part with the largest surface area) is closer to tangent on the bullets with a larger meplate. I would imagine that if you could lock this at a set angle results would be different. Your flat point bullet looks closer to the ideal subsonic rocket nose shape than the pointed version the software draws and it is because of that sharp corner. 
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Offline rsterne

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Re: 12ga Big Bore
« Reply #98 on: February 18, 2019, 04:17:45 PM »
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
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Offline fpjeepy

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Re: 12ga Big Bore
« Reply #99 on: February 18, 2019, 04:56:31 PM »
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

If the calculator gives you a warning as the nose gets shorter because it is not accurate, I would also assume that the least accurate area, is just inside the bounds of the cutoff. And you will notice that this flat point advantage diminishes as the nose gets longer.

I will agree that in your example the black outline would have less drag. But I would argue that if you left the blue "stagnation zone" on the bullet (even as a plastic ballistic tip) it would have even less drag.
  • Anne Arundel, MD, USA

How do you word it... "Air Guns" or "AirGuns"?
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