GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: zandrew on October 16, 2015, 07:05:01 PM
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I have been throwing the idea around in my head for some time about adapting a larger caliber to my Airforce talon and seeing what can be done. I would love to be able to shoot accurately at longer ranges. I like the .257 but I am really interested in seeing what can be done in a .223 with say 50 grain projectile. I figure the lighter weight would be easier to get going fast enough to travel further more accurately. At the same time I am not trying to reinvent the wheel.
I am interested in any info regarding this topic.
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With the smaller calibers like .22 ( .223 ) the limited area for air to work against limits power to some degree.
Larger calibers are more efficient in harnessing the same pressure to make more energy.
Being were still shooting +/- the transonic speed range ideally 950 or less .... You will find MUCH MORE power potential with larger diameter and heavier weights so long as rifles valving can provide sufficient air volume while maintaining reasonably short dwell time.
JMO,
Scott
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With the smaller calibers like .22 ( .223 ) the limited area for air to work against limits power to some degree.
Larger calibers are more efficient in harnessing the same pressure to make more energy.
Being were still shooting +/- the transonic speed range ideally 950 or less .... You will find MUCH MORE power potential with larger diameter and heavier weights so long as rifles valving can provide sufficient air volume while maintaining reasonably short dwell time.
JMO,
Scott
I am wanting to shoot paper strictly so I have no need for energy. I am strictly looking for accuracy and hopefully distance. Thats my interest in the smaller .223.
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With the smaller calibers like .22 ( .223 ) the limited area for air to work against limits power to some degree.
Larger calibers are more efficient in harnessing the same pressure to make more energy.
Being were still shooting +/- the transonic speed range ideally 950 or less .... You will find MUCH MORE power potential with larger diameter and heavier weights so long as rifles valving can provide sufficient air volume while maintaining reasonably short dwell time.
JMO,
Scott
I am wanting to shoot paper strictly so I have no need for energy. I am strictly looking for accuracy and hopefully distance. Thats my interest in the smaller .223.
Plenty to read on the GTA about pellet BC / Velocity / what required for best accuracy.
You start shooting LONG & Heavy .22 cal stuff the barrel twist rate changes up making specialty barrels a go too for the serious target shooter.
Good Luck
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The practical limit is about 950 fps, above that the wind drift increases dramatically.... That works out to 2 FPE per grain of bullet weight, so power is a no-brainer, the bigger the better.... Now you don't need power, so the smaller calibers appear attractive, but for a given projectile shape, the Sectional Density, and hence the Ballistics Coefficient, are proportional to the caliber.... So, in terms of reducing wind drift, once again bigger is better.... There is one thing where the smaller calibers have an edge, and that is the other side of the SD issue.... For any given pressure and barrel length, there is a maximum SD to reach 950 fps, and when you hold the SD constant, bullets in larger calibers get shorter and fatter, and hence have more drag.... This swings the balance back towards the smaller calibers again when you are trying to fight the wind....
Bottom line, if you really want to fight the wind, you need high pressure and a long barrel, to drive the SD to the maximum.... because BC is proportional to SD.... The caliber is secondary, to a large extent.... but the one that gets the most attention, and has the best overall results at long range, is currently the .257.... That is where I would put my effort....
Bob
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The practical limit is about 950 fps, above that the wind drift increases dramatically.... That works out to 2 FPE per grain of bullet weight, so power is a no-brainer, the bigger the better.... Now you don't need power, so the smaller calibers appear attractive, but for a given projectile shape, the Sectional Density, and hence the Ballistics Coefficient, are proportional to the caliber.... So, in terms of reducing wind drift, once again bigger is better.... There is one thing where the smaller calibers have an edge, and that is the other side of the SD issue.... For any given pressure and barrel length, there is a maximum SD to reach 950 fps, and when you hold the SD constant, bullets in larger calibers get shorter and fatter, and hence have more drag.... This swings the balance back towards the smaller calibers again when you are trying to fight the wind....
Bottom line, if you really want to fight the wind, you need high pressure and a long barrel, to drive the SD to the maximum.... because BC is proportional to SD.... The caliber is secondary, to a large extent.... but the one that gets the most attention, and has the best overall results at long range, is currently the .257.... That is where I would put my effort....
Bob
I figured there was a good reason the .257 is the hot ticket. Since we have established there is no logical reason to deviate from the known caliber whats the logic behind twist rate and more importantly grooves and lands? My understanding is that heavier grain bullets like slower twist rate. Why I do not know but that is what I have come across in my research.
I guess I am attracted to the lighter grains since you can accelerate them easier.
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I guess I am attracted to the lighter grains since you can accelerate them easier.
It is a two way street, low mass & weight gets up to speed quickly ... tho also slows down quickly.
Thus the "BC" issue we so frequently speak of.
Sectional density as Bob speaks of above is well worth wrapping your head around, as it is key in long range shooting no matter what launches said bullet / pellet.
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Funny thing about Sectional Density. Doesn't matter if it's a round ball, a wadcutter, or a pointed pellet, if they're all the same caliber and all the same weight, they'll all have the same SD. But the pointed bullet would normally have a higher BC thanks to the lower wind resistance built into it's shape.
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hey-Hey!!!,
I have a .224 boolit-shooting Marauder. The barrel is a .224/.219 liner from TJ's. It measures on the small side( .2234/.218 ) and thus will want sized boolits if they're to avoid large drag. I just got a mold from Lee. With soft alloy, they weigh 56 gr( 55 quoted by Lee ). They have a bore riding section of the nose that gets a fine bit of rifling engraved on them...but they'll be needing a 3k fill to move properly.
39-40 gr is much easier to deal with, and from published BC of 40 gr rimfire bullets traveling at 1080 fps around .095..slowing them down to 950 probably bumps them to a bit over .1. That is still huge compared to pellets. the best of them, the King Heavy sports a BC of ~.05...:)
cheers,
Douglas
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Actually, a roundball will have a different SD in every caliber, and in fact proportional to the caliber.... The BC is the SD divided by the "Form Factor", which is lower for bullets with less drag.... So, yes, a Spitzer can have less drag, although the difference when subsonic is not as great as you might think.... The largest portion of the drag when subsonic is the base drag, which is why I have been working so hard on boattails for airguns.... At our velocities, the back of the bullet is MUCH more important than the front.... but the SD is CRITICAL to improving the BC....
As far as twist rate is concerned, the longer the bullet (for a given caliber) the FASTER you need to spin it (shorter twist rate).... and heavier bullets (for a given caliber) are generally longer.... so need a faster twist, not slower....
Bob
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Yes, a round ball could be a different SD for every caliber.
What I meant was that a 15.43 grain .22 caliber round ball will have the same SD as any other .22 projectile with a weight of 15.43 grains, no matter the shape.
Or, for any given caliber all projectiles of the same weight will have the same SD no matter the length, shape or the BC.
A boattail pellet with a high BC is a great idea. I think I have seen these, but I can't remember what company was making them.
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I think you are referring to the Prometheus Piledriver pellet.... I am working on cast boattail bullets for high powered PCPs.... Search "Whiteout" on the GTA....
Bob
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H+N PYLE DRIVER .177 21 grain sold at PA
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Yes sir, that's the one. I considered that what I was aluding to might be off topic.
And I see the Whiteout uses heavier bullets than I had considered. But I had kind of switched my train of thought towards heavier bullets in 6mm and up.
Granted, I'm not well versed in big bore air rifles, but it would seem that similar principles would apply. Unless pressures prevent their use, a flow through bolt that directs air away from the boat tail and towards the center of the projectile could be advantageous. What I would invision for a large caliber long range air rifle projectile would be a hollow base boat tail with a fast taper hollow point tip similar in appearance to a blend of the Sierra GK and SMK.
I had considered a kind of a wide wasp waist with land width in between groove width rings just behind the tip and at the leading edge of the boat tail, but this design would lower the BC in my guestimation.
Or a more conventional design similar to the Lapua FMJ S, which curiously has a hollow base of sorts.
When talk swings towards SD and BC, it seems the 6.5 is always in the conversation. But I don't see any reference to it concerning air rifles. Fast twist barrels are prevalent here, and high SD and BC are achieved with relatively lightweight conventional bullets. A 110 to 115 grain bullet/pellet in 6.5 should be in the range of a 155g .308 SD, and high BC is the norm in 6.5
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Airguns are only just beginning to push the limits of SD, and there is good reason for that.... The higher the SD the more barrel length and pressure you need to drive it at a decent velocity.... If you want to reach 950 fps, and you have a PCP with a 24" barrel running 3000 psi, forget about anything with an SD over 0.17, you just won't make it.... For an SD of 0.25, you need about a 30" barrel and 3600 psi to get into the mid 900s.... and even then it better be a POTENT gun to have a chance of doing it (using air)....
As far as reaching the maximum potential in an caliber, a flow-through bolt will never do it, there is too much restriction in the port area, you need full bore-sized porting to get to the above numbers.... I use a retracting bolt with a square nose that seats the bullet past the port and then retracts completely out of the airflow.... The other suitable method is an axial flow design, like a Condor....
Bob
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I see. So low SD/high BC could be the way to go with a more conventional air rifle that doesn't have extreme pressures or super long barrel?
Maybe something like the Crosman Powershot is worth looking into, with it's long plastic base. Or an all lead pellet with a long hollow skirt to keep BC up and weight/SD down.
In .308, a 110 grain is about the max weight to keep SD below .17, and in a conventional solid base spritzer only gets about .260 BC. A long hollow base and possibly plastic tip could raise BC and keep SD at a minimum.
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There is a very close relationship between S.D. and B.C. so no that will not work, as you drop weight so you drop S.D./B.C...
I think the best that can be done for more normal power levels is to shorten the round as much as possible while keeping as much of the boattail as possible...
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From my limited experience, bullets with equal SD can vary quite a bit in BC.
While SD is in the equation for calculating BC, the shape of the projectile plays a heavy role in BC.
A clear example is the difference between two different designs of 175 grain .284 bullets. Both have an SD of .310, as do all 175 grain .284 projectiles. But the differences in the BC of the 175 gr Hornady Interlock RN(.285 BC) and the 175gr Berger XLD(.658 BC) vary wildly.
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yep but those are supersonic rounds... so the Form factor will play a much bigger role...
http://www.gatewaytoairguns.org/GTA/index.php?topic=70470.0 (http://www.gatewaytoairguns.org/GTA/index.php?topic=70470.0)
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Now at subsonic the boat tail config (more of Bobs work)...
http://www.gatewaytoairguns.org/GTA/index.php?topic=93524.40 (http://www.gatewaytoairguns.org/GTA/index.php?topic=93524.40)
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May take me a bit to wrap my head around all that.
But I keep thinking back to a Brenneke type slug. Which is suspiciously similar to the Powershot.
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Its very hard to keep a fair comparison when evaluating different boolits. I find that if I compare them all at the same velocity, I tend to get a clearer, more fair comparison. So with the McDrag spread sheet, I set all of my velocities at 950. SD is of course unchanged with regard to velocity but the BC does change. Also input the same barrel lengths while comparing. Thanks to Bob's wonderful work, we can now get a fair estimation of potential velocity based on SD, pressure and barrel length. If you have a comparison of same caliber projectiles, and the SD exceeds what could possibly reach 950fps, then you know you'll need more barrel length and or more psi. But knowing how to estimate the fps based on SD is the key. If the SD is too high to reach the 950fps goal, then you have what I would consider a fair comparison based just of capability of the delivery system. Often you will see that the BC is higher but since the initial velocity was so much lower, the trajectory just isn't adequate for long range work.
These Tools are on the web and can be fairly easily adapted to our realm of work. The McDrag spreadsheet is on the web and can be down loaded free. The Koble web sight has a couple of online calculators that are awesome tools. Garbage in, Garbage out though. Keep in mind that bearing length is important and that longer is sleeker. I think Bob would agree, approximately 60% of caliber is the min bearing surface length, definitely not less.
Thanks Bob for all the hard work and data building. You have paved a path to enlightenment.
I've though about the 6.5 also but a reasonably priced barrel isn't really available. At least not in the realm of air gun building. (opinion). For the sake of weight management. It seems that the thinner liners, set in CF, are the logical straight forward approach. Then you get into the liner under tension as the advanced approach.
FWIW
Bill
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I haven't looked at them all, but Green Mountain has decent prices on barrel blanks. Although a good bit of them are heavy bull barrels that would probably take a lot of machining to fit an airgun.
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So I came up with a rough sketch of a design that I think could have some promise.
It's a sort of semi-sabot with a teardrop shaped bullet and a sabot with a cupped base that would only cover the tail of the bullet, enabling the front portion to remain in contact with the rifling for better stabilization.
The sabot would disconnect upon leaving the barrel.
Actually, I think they could be loaded in two pieces, or placed together just before loading, in an air rifle. Therefore, eliminating the chance of the sabot staying attatched as they leave the barrel.
Prolly not feasible, but just a thought.
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I sense a slight confusion here between BC and Form Factor.... If you make a bullet less dense, to decrease the SD, you will also decrease the BC, even if the FF remains the same.... The only way to keep the same BC with a lighter SD is to gain the same percentage on the FF....
Bob
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After thinking that the teardrop bullet might be too heavy, I decided that a semi-wadcutter hollow point might be a better design(Kind of like a crow magnum). And then I read some of Bob's posts saying that for between 800 and 1000 fps, or somewhere around those numbers, that the raindrop was a poor design. Or at least not necessary, with the (air-cap?) forming on the face of a flat point design. Which is a bit confusing, considering that a lot of airgunners prefer domed pellets, maybe only for their penetration or because the head size is a good match for most barrels.
Anyway, I came up with a similar but new sketch.
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I sense a slight confusion here between BC and Form Factor.... If you make a bullet less dense, to decrease the SD, you will also decrease the BC, even if the FF remains the same.... The only way to keep the same BC with a lighter SD is to gain the same percentage on the FF....
Bob
Actually Bob, in my sketches I was going by your theory that a long boat tail is the best way to make use of BC at sub-sonic speeds. There's quite a bit of FF behind the idea, as the boat tail in this case comes to a long point after the half-sabot releases as the bullet exits the barrel.
Maybe the tail is a bit extreme in design?
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For the most part, the choice of shapes for airgun pellets has been flat (wadcutter), pointed, or domed (some domed, the better ones a true hemi-sphere).... For whatever reason, we have not really experimented with the type of nose used in bullets, with a tangent ogive and a flat at the front (Meplat) that is less than the full diameter.... Something like this....
(http://i378.photobucket.com/albums/oo221/rsterne/Bullet%20Casting/30%20cal%20Pellet%2054_61%20gr_zpslnsvtqvd.jpg) (http://s378.photobucket.com/user/rsterne/media/Bullet%20Casting/30%20cal%20Pellet%2054_61%20gr_zpslnsvtqvd.jpg.html)
At least in theory, that should have less drag than a round-nose design.... Imagine the stagnation zone and you have an ellipse travelling long-ways, instead of a circle.... However, it still has the skirt, and the associated drag of not only the full caliber diameter base, but the flare in front of that from the waist.... If you could figure out a way to make a saboted bullet and maintain accuracy, it may be worth the trouble.... I don't think you have to go right to a point, they haven't used that idea in racecars since the 1930s (OK, maybe the 50s).... Any bullet has a "wake zone" behind it, the boattail is a matter of trying to shrink it in size.... The ballistics programs break down if you make the boattail less than half the caliber.... I think the ideal shape for what you are thinking might be like a football with both points cut off....
Bob
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I sense a slight confusion here between BC and Form Factor.... If you make a bullet less dense, to decrease the SD, you will also decrease the BC, even if the FF remains the same.... The only way to keep the same BC with a lighter SD is to gain the same percentage on the FF....
Bob
Also, the idea was not to make the projectile less dense, but to increase BC without adding density.
As by increasing Form Factor.
A short bullet at a certain weight has the same sectional density as a long bullet of the same weight as long as they are the same caliber, even if the materials used to make the projectiles have a different density themselves.
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For the most part, the choice of shapes for airgun pellets has been flat (wadcutter), pointed, or domed (some domed, the better ones a true hemi-sphere).... For whatever reason, we have not really experimented with the type of nose used in bullets, with a tangent ogive and a flat at the front (Meplat) that is less than the full diameter.... Something like this....
(http://i378.photobucket.com/albums/oo221/rsterne/Bullet%20Casting/30%20cal%20Pellet%2054_61%20gr_zpslnsvtqvd.jpg) (http://s378.photobucket.com/user/rsterne/media/Bullet%20Casting/30%20cal%20Pellet%2054_61%20gr_zpslnsvtqvd.jpg.html)
At least in theory, that should have less drag than a round-nose design.... Imagine the stagnation zone and you have an ellipse travelling long-ways, instead of a circle.... However, it still has the skirt, and the associated drag of not only the full caliber diameter base, but the flare in front of that from the waist.... If you could figure out a way to make a saboted bullet and maintain accuracy, it may be worth the trouble.... I don't think you have to go right to a point, they haven't used that idea in racecars since the 1930s (OK, maybe the 50s).... Any bullet has a "wake zone" behind it, the boattail is a matter of trying to shrink it in size.... The ballistics programs break down if you make the boattail less than half the caliber.... I think the ideal shape for what you are thinking might be like a football with both points cut off....
Bob
I guess my thinking of coming to a point wasn't influenced by a race car, which normaly has other needs such as adhearing to length restrictions as well as the need for full width to facilitate downforce on the back of the car. But more akin to the trailing edge of an aircraft wing.
The idea of the non-attatched semi-sabot was to make full use of the limited pressure in an airgun. And the idea that it did not fully encapsulate the projectile to let the 60% of diameter bullet contact with the lands and possibly grooves for greater stability and accuracy.
Definitely an unproven design. But I don't think it has been disproven yet.
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Another thought about the stagnation zone and it's effect overcoming drag at subsonic velocities.
When you brought up race cars, it got me thinking. Race cars are subsonic. Yet there aren't any that are shaped like a bus in the front. Below are a couple of pictures of the car that set the land speed record, slightly above Mach 1. Note the sharply pointed nose of the car.
I suspect there will come a day when a pellet with a long pointed plastic tip will be used for long range subsonic air rifle shooting.
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Things change completely when you need to approach Mach 1.... The transonic zone is from Mach 0.8-1.2, and things change dramatically in that range.... Here is the drag curve of the G1 projectile....
(http://i378.photobucket.com/albums/oo221/rsterne/Ballistics/G1BallisticsModel_zps5e9e7901.jpg) (http://s378.photobucket.com/user/rsterne/media/Ballistics/G1BallisticsModel_zps5e9e7901.jpg.html)
and here is what it looks like....
(http://i378.photobucket.com/albums/oo221/rsterne/Ballistics/g1_zps09zm9zd2.jpg) (http://s378.photobucket.com/user/rsterne/media/Ballistics/g1_zps09zm9zd2.jpg.html)
Current airgun pellets have an even steeper drag curve in the transonic region, which is why we keep them subsonic (if we have any sense), which is in the yellow area on the graph above.... Incidently, wind drift follows the drag curve, so pushing near Mach 1 may gain you a flatter trajectory, but the wind will push the pellet even further off course.... Last time I looked, gravity was a constant, but the wind was not.... Add to that the inherent internal inefficiencies of trying to push a pellet near Mach 1 using air and you get a double whammy.... You burn more air to get there, and then when the pellet exits the muzzle it gets slammed with horrendous drag and loses that extra hard-earned velocity in the first few yards.... LITERALLY.... Stay below Mach 0.85 or so, and certainly below Mach 0.9 (1000 fps) and you will be a LOT happier with the results....
Bob
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Bob on the .224 that you and Sweede came up with is 43g and wants a pretty quick twist compared to the easily available barrels that are 14 twist..?
What guided that choice? can he cut a .6-.8 body (the .216 section) instead of a .128
I was so hoping for a O.A.L. closer to .38-.40 or so and a weight of 38-40g... then I could hollow point to about 35g.. ;)
http://noebulletmolds.com/smf/index.php/topic,1132.0.html?PHPSESSID=6c6a4q5m9rrrtksbs4hkdtccq2 (http://noebulletmolds.com/smf/index.php/topic,1132.0.html?PHPSESSID=6c6a4q5m9rrrtksbs4hkdtccq2)
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I've never suggested that the reason for attaining a higher BC was to obtain more speed, but instead to carry the speed available more efficiently. I would suggest that a bullet with a higher BC would paint a different picture in your drag coefficient arcs.
And with the looks of that graph, with that bullet, I'm not sure why 892 fps shouldn't be the goal.
As far as gravity and wind, time and distance play a major factor also.
It is true that gravity is a constant, in a progressive sense. Some might confuse a gravitational rate of 32 fps/s as equaling 16 feet in a half second, but due to gravities progressive nature an object will fall far less than 16 feet in it's first half second of free fall.
Similarly, while an object traveling at a rapid rate might have more pressure exerted on it by wind, it will have traveled a farther distance during the time the wind has to push it than the same object traveling at a slower pace. And an object with a lower BC will be blown further off course than one with a higher BC ober the same distance.
Again, I wasn't trying to convince anybody to try and attain a speed nearing mach 1. I just thought that a more efficient projectile with a higher BC would be of some value to whoever mihht be trying to push the limits of extreme long range shooting with a 950 fps air rifle of any caliber.
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That design is 2 calibers long, and I didn't design a lighter one because I couldn't imagine anyone would want one.... There is a .217 cal 37 gr. that I did make shorter, and the reason was to fit Hatsan magazines.... Even that requires a 12" twist.... Simply shortening the middle of the bullet would shorten the support in the rifling, and I would not recommend that.... It's not something Al could do anyway, a different cutting tool is made for every design.... If the bullet was done at 1.5 calibers long it would be about 33 gr. and require a 17" twist.... At 1.75 cal long it would be 38 gr. and require a 14" twist.... It sounds like that is what you are looking for, and I could add that to the list, whether it would ever reach production or not would depend on demand.... You can see exactly what it would look like by looking at the .308 cal 100 gr.... scale that down to .224 and it would be 38 gr....
http://noebulletmolds.com/smf/index.php/topic,1121.0.html (http://noebulletmolds.com/smf/index.php/topic,1121.0.html)
The good thing is that it would work fine in the TJ's 14" twist barrel.... but then the 43 gr. may as well, only trying it would find out for sure....
Bob
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I misunderstood.... your reference to the pointed nose on the Thrust SSC which was designed to break Mach 1 confused me.... Yes, Mach 0.8 (~900 fps) is a great place to be with an airgun.... You must realize I have been studying BCs for a while.... do a search on Bob's Boattails, or check out the Engineering Gate for a post on using the "McDrag" program to optimize airgun bullets.... As far as wind deflection goes, the key is the DIFFERENCE in the time of flight between a vacuum and in the real world, not the time of flight per se.... That is why the Drag Coefficient is so important.... BC takes into account the curve in the G1 profile (or another, similar one), and a constant BC does NOT mean constant drag or wind deflection.... As I said, the wind deflection follows the drag curve above.... Check out the JBM Drift calculator, and input various values for the muzzle velocity and you will be surprised by the results.... Here is an example, actually three examples....
(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)
Note, there are for bullets, not pellets, including the super-slippery Sierra Matchking.... To achieve the same wind drift as that bullet has starting at 800-900 fps you have to push the muzzle velocity all the way to 2600 fps (way out of airgun territory).... Any velocity in between will have greater drift....
Bob
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Bob, I do have a lot to learn. It's an ongoing struggle :D
The graph is similar to yours with the G1. But it does show that the heavier, higher BC bullet has less drift across the board than the lighter blockier bullets.
And it brings up another question in my mind. This one regarding K.O. and his 43 grain .217 pellet.
It seems to me that the reason for the 950 fps for small caliber air rifles is due the the greater effect outside forces have on the lightweight low SD & BC pellets and the fairly short distance that targets are set at.
And when moving up in weight to around 40 grains, there may be some benefit to a slightly higher velocity. Say the 1060 fps that .22LR target ammo uses? I would imagine that the larger forces that are placed upon the bullet would be short lived as it loses initial velocity quickly and drops into the sweetspot over the longer distsnces that would most likely be targeted.
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The Blue Flame also has a fairly pointed profile. It only went 924 feet per second.
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well I am looking at it from the view of what many have(a stock .25 Mrod) honestly an easier path to a higher B.C. round than Mods for high power...
with a 10-15 pound spring and a 24" barrel I figure a stock Mrod could hit 65 fpe for near a mag with a 2%-4% es...
that would not require being tethered or a tanker conversion in other words easy and assessable to those that use a hand pump...
About the best you could get at that level but would still be useful to those that have more fpe on tap..?
I did notice that the boat tail is .1 long on it and on the .250 and .217 it is .89 so I guess it could be shortened a touch(could be done by hand after casting) (with slight increase in drag?)
Now 65 fpe with 43g is 824 fps just a bit slower than I want to go my target is 850-950 fps so losing the weight would be a plus but mainly it is the twist rate... because as drawn just a hollow point would bring it down to 39-40g and should get about 850 fps...
but hollow pointing the 14 twist round to about 34-35g well that would be just about perfect for 950 fps...
Now me I am nuts enough to send it out of the 1:16 Marlin .22WMR Barrel but that is besides the point...
The only other .224 right now is he that opposes the Puppeters(Doug) and he has power to spare but a 1 :14 twist...
Me I like the idea of being able to switch between the stock .25 green mountain pellet barrel and a .224 barrel with maybe a spring and tport change...
.25 for shooting up into the trees and .224 for the open desert...
oh I think the B.C. of the BBT .224 listed has been estimated a bit low a 30g .22 at 900fps has a B.C. of about 1.4 iirc...
But anyways I do think designing for a 14" twist would be attractive to many just because it would not require a $$ custom barrel... just a $ barrel... and is more in reach power/shot count wise...
Thanks Bob and I would be interested but it would be about 3 or 4 months before I could actually purchase a mold... expecting my first grandchild on the 28th ;D ;D ;D and then Christmas and the birthdays of my Kids are one a month till Feb...
plus I just could not resist a brand new Bsa Buc for what it was going for and have to finish paying it off... ;)
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And it brings up another question in my mind. This one regarding K.O. and his 43 grain .217 pellet.
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first is not my 43 grain .217 pellet...
I am talking about a .224 bullet... of Bobs Design...
second he did design a 37g .217 bullet (not pellet)... and not 43g...
http://noebulletmolds.com/smf/index.php/topic,1127.0.html (http://noebulletmolds.com/smf/index.php/topic,1127.0.html)
But as much as I would like to see a .217 BBT (Bobs Boat tail) I once again wonder if the twist required is a bit to much requiring a custom barrel...
Me I am looking at it from the view of broadening the amount of rifles capable of sending the round out..
Now at .250 and above well the amount of air used needs a big tank even with lightening the round...
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I am also so close to what is needed for that .217 round except for the twist rate...
I have a rather unique 22lr barrel that it would send it out if it was shorter and dropped with a .22 drive band...
it has a slightly faster twist than normal at 1:15.75 and is choked to about .218 groove and .212 land...
I do not know where a 1:12 or even 1:14 .22 pellet barrel could be found..? almost all I know of are 1:16 or greater twist...
so yep so close to what I need but not quite... I could cast a slug with a screw in it and lap it just a touch larger(but may cause out of round) but I would have to knock off the boat tail for the twist to work... and that just would defeat the purpose...
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For the relatively slow twist of most airgun barrels, it is simply not practical to make a boattail.... by the time you shorten the BT and increase the diameter to allow it to use the slow twist rate, you may as well just use a flat-base bullet with a gas-check recess....
Increasing the velocity up into the mid 1000s will still increase the wind drift more than what you get at 900.... Even the 25 yd. Benchrest shooters stay below 900 fps to achieve the minimum possible drift.... .22LR target ammo (subsonic) has significantly less drift than the HV does.... As I said, play with the JBM calculator, select any bullet you want from their dropdown menu, and start putting in velocities between 500-1500 fps and you will get a plot of wind drift similar to the above....
http://www.jbmballistics.com/cgi-bin/jbmtraj_drift-5.1.cgi (http://www.jbmballistics.com/cgi-bin/jbmtraj_drift-5.1.cgi)
The first one I picked, an Aquila .22LR, drifts only 4.1" at 850 fps, but 6.7" at 1400 fps at 100 yards....
Bob
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Just out of curiosity, I was reading about the Eley TenEx. A lot of the information doesn't apply, such as the ability to remain stable at 1085 fps, since the bullet is a 40 grain solid chunk of lead and not a hollow base lighter weight pellet. But it does have the "football with the ends cut off" shape.
The one similarity to subsonoc air rifles that I found of value was the emphasis on the importance of the shape of the nose. It was very similar to Bob's draft. And the particular feature that they accredited it's accuracy to was the sharp edged cut flat nose that promotes the hollow space of air ahead for the bullet to travel through. The bump in the center is just a result of the cutting the sharp edge, and not a design feature.
But while these bullets are used in competition out to 100 yards, or maybe meters, they claim the design is most effective out to 50 yards.
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Not really a football, the rear shoulder is parallel to the bore, only there for chambering in the cartridge.... The nose shape is a typical Tangent Ogive with Meplat, however, which from everything I have read is the best for subsonic and low transonic velocities.... It actually works well right up to Mach 1, but the Meplat has to shrink in diameter or the drag goes up.... Right at Mach 1, a 30% Meplat is optimum, and by the time you get to Mach 2, that shrinks to 10-20% of the caliber.... The little "nub" on the front is proof of the stagnation zone, it has no effect on the flight or drag as it's in a dead air space travelling with the bullet.... I have seen photos of the TenEx where the size and shape of that nub is inconsistent within one box of ammo.... Disconcerting, but irrelevant apparently.... as they are VERY consistent in weight, one of their claims to fame....
Bob
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hey Bob on the .217 BBT maybe if I get the mold and then sand(cut, whatever)the round to ~85% meplat then it would be closer to a stable round. In this thread you conclude at .8 Mach the Meplat size had little effect from 20%-80%...
http://www.gatewaytoairguns.org/GTA/index.php?topic=94920.0 (http://www.gatewaytoairguns.org/GTA/index.php?topic=94920.0)
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So what conclusions can we draw so far if we are trying to determine the "best" Meplat size?.... Well, below Mach 0.8 it doesn't matter.... If we cared about the Supersonic range (above Mach 1.2), the 80% Meplat is too big.... For short bullets, we can also eliminate the thinner Meplats, as their drag starts to increase sooner.... In the Transonic range, this leaves us with choosing between Meplats of 20-80%.... It appears that for shorter bullets, a Meplat of 60-80% is optimum (thank you, Elmer Keith!), extending the low drag plateau up to Mach 0.9.... while for longer bullets 20-60% looks like the optimum, again extending the low drag plateau to Mach 0.9.... Are you ready for round two?.... Let's set the Meplat at 60% and vary the nose length and see what happens.... and again with a Meplat of 30%....
"
So in the interest of a round that would work in most current barrels do you think the compromise would work... For me half the reason for going to a cast round is the independence of it
I think it would still outperform most pellets? it would be basically a rebated boat tail semi wad cutter, or do you think I am overlooking something?
I just wish that there was more research done with subsonic rebated boatails I really do get the feeling that since the Cg is more forward that it will need les twist than a flat based bullet of the same length...
they say that it also would move the center of pressure forwards so it would need more twist iirc,
but to me that is only true near and past 1150 fps..? My gut says I am right... but it has been known to be wrong more than once.. ;)
The other thing I would love to figure out is why the Marlin barrels seem to do ok with the 60g subs while they tumble out of other 1:16 .22 barrels?
Long winded but shoots a little past 8 min in... https://www.youtube.com/watch?v=m9-8sbPMgJc (https://www.youtube.com/watch?v=m9-8sbPMgJc)
and this I am pretty sure is a Marlin 980v... https://www.youtube.com/watch?v=K1w01G01S3I (https://www.youtube.com/watch?v=K1w01G01S3I)
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I think some older Marlins had 12 grooves and then switched to 16 grooves, botg 1 in 16 twist. Don't know if the number of grooves makes any difference on stabilizing heavier bullets or not.
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Pretty sure that's a Savage Mark II FV in that video.
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Pretty sure that's a Savage Mark II FV in that video.
Hmmm with a closer look It looks like you are right...
So what Voodoo is keeping the 60g round from tumbling..? ???
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I think some older Marlins had 12 grooves and then switched to 16 grooves, botg 1 in 16 twist. Don't know if the number of grooves makes any difference on stabilizing heavier bullets or not.
I am using a Marlin 883N .22 Mag barrel for my .224 project they have 20 lands and grooves...
I used a used Glenfield model 60(same as Marlin 60) to practice turning it down to 9/16 first... just finished turning the .22mag down...
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Now I'm going to have to get out my magnifying glas and count some grooves.
By the way, I've been a long time admirer of your long tube 13xx builds. I plan on having one in .22 in a few months.
The 1377 standard tube carbine is up first though. It'll be a rear cocker.
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The size of the Meplat has little to do with the twist rate, some, but nothing compared to the diameter of the boattail base.... The easiest thing you could do to make the 43 gr. work in a slower twist would be to machine off the back of the mold to shorten the boattail and increase the diameter.... I can make that calculation for you.... It will also lighten the bullet, which seems to be what you want....
Bob
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https://www.augustana.ualberta.ca/~hackw/mp480/exhibit/ballisticsMP480.pdf (https://www.augustana.ualberta.ca/~hackw/mp480/exhibit/ballisticsMP480.pdf)
Here's an actual published paper on ballistics. I thought it was funny that "Serving the Darkside" was in the title! :D
REAL science!!!
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K.O., here is the skinny on the .224 cal 43 gr.... As it stands, in a 14" twist barrel, it has the following Stability Factors (less than 1.0 is unstable, 1.5 is recommended, but generally 1.3 works just fine)....
Mach 1.... 0.8
1000 fps.... 1.0
900 fps.... 1.1
800 fps.... 1.2
700 fps.... 1.3
So the stock 43 gr. should be fine at 700 fps and less, and should get more stable as it goes downrange because the forward velocity decays faster than the RPM.... If you shorten the back of the bullet by just 0.030", that increases the diameter of the boattail base by only 0.008", but that, plus shortening the bullet, increases the stability to the following....
Mach 1.... 1.0
1000 fps.... 1.25
900 fps.... 1.4
800 fps.... 1.5
Now you could push the bullet to at least 950 fps without an issue.... Just imagine, that big a difference from less than 1/32" removed from the base of the bullet.... :o
Incidently, it would only reduce the weight by about 2.6 gr, to about 40 gr....
Bob
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thanks Bob I had to go take care of a slight emergency for a friend and just got home... need to go get cleaned up and will be reading a bit more carefully...but the quick scan is reading well...
slight misunderstanding on the last because of me thinking I was being clear and wasn't (Concentration probs strike again) :-[ :(
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The size of the Meplat has little to do with the twist rate, some, but nothing compared to the diameter of the boattail base.... The easiest thing you could do to make the 43 gr. work in a slower twist would be to machine off the back of the mold to shorten the boattail and increase the diameter.... I can make that calculation for you.... It will also lighten the bullet, which seems to be what you want....
Bob
what I meant about
"
hey Bob on the .217 BBT maybe if I get the mold and then sand(cut, whatever)the round to ~85% meplat then it would be closer to a stable round. In this thread you conclude at .8 Mach the Meplat size had little effect from 20%-80%...
"
was to shorten the nose after casting until it was stable with a 1:16 twist and that would increase the meplat size...
the price paid would be a touch more drag generated at the nose..? If I understand correctly shortening the boat tail would have a bit larger effect on drag...
but decking the mold and shortening the boatail would be less work to get a stable round in the end...for currently available barrels...
edited for clarity (reread and my occasional concentration probs are showing)**
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K.O., here is the skinny on the .224 cal 43 gr.... As it stands, in a 14" twist barrel, it has the following Stability Factors (less than 1.0 is unstable, 1.5 is recommended, but generally 1.3 works just fine)....
Mach 1.... 0.8
1000 fps.... 1.0
900 fps.... 1.1
800 fps.... 1.2
700 fps.... 1.3
So the stock 43 gr. should be fine at 700 fps and less, and should get more stable as it goes downrange because the forward velocity decays faster than the RPM.... If you shorten the back of the bullet by just 0.030", that increases the diameter of the boattail base by only 0.008", but that, plus shortening the bullet, increases the stability to the following....
Mach 1.... 1.0
1000 fps.... 1.25
900 fps.... 1.4
800 fps.... 1.5
Now you could push the bullet to at least 950 fps without an issue.... Just imagine, that big a difference from less than 1/32" removed from the base of the bullet.... :o
Incidently, it would only reduce the weight by about 2.6 gr, to about 40 gr....
Bob
Thanks for the effort Bob I tend to estimate what is needed and my gut was thinking that it would need shortening by about .06 to be stable in a 1:14 barrel but just .03 is a bit of a shocker...
So since I am using a 1:16 which works well with .22lr at 40g rounds it would seem even at shortening by .03 would work even if the Microgroove barrel is not a help in reducing twist needed...
I am interested in lightening the round for sure... I think that .224 boat tail boolits will outperform just about any .25 pellet...By having a round that keeps the fpe requirments near that achievable with a near stock Mrod it just might get enough people interested for us to get some molds made... and then if they prove out then it will build..."Build it and they will come" ;)...
I do think that for the lower fpe rifle a 1.75 caliber version would be the optimum...
But then again it is probably not that much of a performance penalty if the tail is shortened rather than the body(as drawn) and as drawn would be better for those that have fpe to spare... Meaning those already sending cast rounds out...
So yep decking the .224 mold by .030 would be acceptable to me and not muddy the choices even more... I think we will have a hard enough time just getting enough interest in the .224 as it is...
Sort of the chicken or egg thing... people have not done it because the molds are not available for the current barrels but the molds are not available because no one is doing it...
Me I am willing to carve my rounds by hand if I have to...
Heck I bet I could deck the 43g .224 mold and then after casting shorten the nose for even more weight loss and that combined with different hollow points and non hollows get anywhere from about a 34g-40 grain round... some where in there I am sure I would find the round that suited a mild tuned Mrod...
Sorry for taking so long to get back but I had to help my buddy fix a pipe in a muddy crawlspace and then my back tweaked on me a bit...
Thanks for your efforts on trying to move things forwards, I did register on the N.O.E. forum and cast my votes for the 37 grain .217 and 43 grain .224. 8)
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I have just drawn two new, shorter, airgun caliber boattails and sent them to Al.... a 0.217" 29 gr. for a 16" twist, and a 0.250" 40 gr. for a 20" twist....
Bob
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Now I'm going to have to get out my magnifying glas and count some grooves.
By the way, I've been a long time admirer of your long tube 13xx builds. I plan on having one in .22 in a few months.
The 1377 standard tube carbine is up first though. It'll be a rear cocker.
Thanks I had fun finding out what could be done sticking with just the pump cup and pretty much stock parts with some mods.
flat tops would be faster and more efficient but I also wanted low budget...so there is a lot of room for improvement... But they all will hit a quarter at 30 yards very reliably and .5 groups at times so I am happy...
the 1322XLT needs to be a rear cocker I keep breaking and bending the cocking pin...
I have most of the parts for an extended valve Mk13xx that would take 40-45 pumps to hit 1500 psi with a gage it just might make a good ACP.
I wonder what rifling Savage .22lr is currently using is it still 6 unequal and ~ .025 land .090 groove
http://www.pochefamily.org/books/RimfireBullets.htm (http://www.pochefamily.org/books/RimfireBullets.htm)
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I have just drawn two new, shorter, airgun caliber boattails and sent them to Al.... a 0.217" 29 gr. for a 16" twist, and a 0.250" 40 gr. for a 20" twist....
Bob
Will be watching for them.. ;D
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Just out of curiosity, I was reading about the Eley TenEx. A lot of the information doesn't apply, such as the ability to remain stable at 1085 fps, since the bullet is a 40 grain solid chunk of lead and not a hollow base lighter weight pellet. But it does have the "football with the ends cut off" shape.
The one similarity to subsonoc air rifles that I found of value was the emphasis on the importance of the shape of the nose. It was very similar to Bob's draft. And the particular feature that they accredited it's accuracy to was the sharp edged cut flat nose that promotes the hollow space of air ahead for the bullet to travel through. The bump in the center is just a result of the cutting the sharp edge, and not a design feature.
But while these bullets are used in competition out to 100 yards, or maybe meters, they claim the design is most effective out to 50 yards.
I think consistent case rim thickness is also a part of it.. ;) also consistent seating depth in the case...
shows case variance... https://www.youtube.com/watch?v=oqM-SHZlZjM (https://www.youtube.com/watch?v=oqM-SHZlZjM)
this is a lot of talking but it does show length/seating variance in cheaper ammo... https://www.youtube.com/watch?v=N-xoWXNp9hQ (https://www.youtube.com/watch?v=N-xoWXNp9hQ)
Have you seen the Paco Kelly fixing the nose kit... me personally I do not want to hammer ammo...
I plan on eventually using a https://www.youtube.com/watch?v=inEmsBcAwho (https://www.youtube.com/watch?v=inEmsBcAwho) or something close to it help Blueprint my rounds... maybe just a modded nose punch type thing..?
I wonder if I can make my own .217 sizer..? I know there is some one that is making custom sizers for about $25...
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Yeah I saw that Paco Kelly thing a while back. But I just shoot'em stock.
About that Eley Ammo, yeah the rim is part of it.
They also have a special way they make the primer flow out and meter it very precisely. There's even have a special name for it. They say the primer is a critical factor because it provides more propellant than the powder does.
And then they do all kinds of other crazy stuff like checking the humidity and temperature in the place where the powder comes from on the day they made a certain batch.