.308 cal 200 gr. BBT Whiteout

[rsterne]

If you have been following the thread on boattail development.... http://www.gatewaytoairguns.org/GTA/index.php?topic=93524.0 .... you will have realized that when I figured out it was possible to duplicate the ballistics of a .300 AAC Blackout with a powerful enough PCP that I changed horses in mid stream.... First a little history.... Rizen 1 asked me if I could develop a bullet for a .308 that could start at about 1500 fps and stay supersonic for 200 yards.... I told him that it might be possible, but when I started looking into it, I quickly realized that was the worst possible velocity range to work in for wind drift.... In addition, that was 750 FPE, and I thought that was a stretch, even for an Extreme .308 on Helium.... I started working on optimizing a 200 gr. boattail for subsonic flight, instead of the 150 gr. for supersonic, and the result is shown below....



All of life is a compromise, and bullet design is no different.... The numbers told me that an 8R Ogive was the best choice, but when I drew it out, it just didn't look right, and I had to shorten that a bit so that the nose ended up under half the overall length.... A 2" radius gave me a 6.67R Ogive, and to keep the 200 gr. weight the bullet is 1.285" long.... The optimum twist is 8", perfect for 1050 fps, and it should still be stable at Mach 1, with a Stability Factor of 1.3.... The Ballistics Coefficient peaks at 1000 fps, so the optimum muzzle velocity over 200 yards is 1030 fps, and it should still be going 960 fps at 200 yards, and have less than 2 MOA of wind drift in a 10 mph wind at that range.... The JBM Ballistics Calculator says that over that velocity range the G1 BC is a staggering 0.80-0.855.... I think a fairer measure would be to use the G7 (boattail) standard, where the BC over that velocity range is 0.351-0.367....

I have sent the design to Veral at LBT to make sure that he can make a mold for it, and I've got my fingers crossed that his production methods don't dictate further changes.... We shall see.... BTW, the name "Whiteout"?.... obviously a play on the word Blackout, and suitable for a bullet from the Great White North, don't you think?.... 

Bob

[YEMX]

This makes me want a .308! Dangnabbit Bob! 

[Rizen 1]

I love it!  cant't wait to see how this all comes together.....

[jr460]

If you have been following the thread on boattail development.... http://www.gatewaytoairguns.org/GTA/index.php?topic=93524.0 .... you will have realized that when I figured out it was possible to duplicate the ballistics of a .300 AAC Blackout with a powerful enough PCP that I changed horses in mid stream.... First a little history.... Rizen 1 asked me if I could develop a bullet for a .308 that could start at about 1500 fps and stay supersonic for 200 yards.... I told him that it might be possible, but when I started looking into it, I quickly realized that was the worst possible velocity range to work in for wind drift.... In addition, that was 750 FPE, and I thought that was a stretch, even for an Extreme .308 on Helium.... I started working on optimizing a 200 gr. boattail for subsonic flight, instead of the 150 gr. for supersonic, and the result is shown below....



All of life is a compromise, and bullet design is no different.... The numbers told me that an 8R Ogive was the best choice, but when I drew it out, it just didn't look right, and I had to shorten that a bit so that the nose ended up under half the overall length.... A 2" radius gave me a 6.67R Ogive, and to keep the 200 gr. weight the bullet is 1.285" long.... The optimum twist is 8", perfect for 1050 fps, and it should still be stable at Mach 1, with a Stability Factor of 1.3.... The Ballistics Coefficient peaks at 1000 fps, so the optimum muzzle velocity over 200 yards is 1030 fps, and it should still be going 960 fps at 200 yards, and have less than 2 MOA of wind drift in a 10 mph wind at that range.... The JBM Ballistics Calculator says that over that velocity range the G1 BC is a staggering 0.80-0.855.... I think a fairer measure would be to use the G7 (boattail) standard, where the BC over that velocity range is 0.351-0.367....

I have sent the design to Veral at LBT to make sure that he can make a mold for it, and I've got my fingers crossed that his production methods don't dictate further changes.... We shall see.... BTW, the name "Whiteout"?.... obviously a play on the word Blackout, and suitable for a bullet from the Great White North, don't you think?.... 

Bob

Hello Bob
I just have to ask where did you come up with 1500 fps with a 200 gr bullet(will duplicate a 300 black out) you are over 400 fps faster than a sammy speck 300 black out.Not trying to be a wise guy but you are way off base on this one.
David

208 GR. HDY A-MAX
Starting Loads Maximum Loads
Manufacturer   Powder   Bullet Diam.   
C.O.L.
Grs.   
Vel. (ft/s)
Pressure
Grs.
Vel. (ft/s)
Pressure
IMR   IMR 4198   .308"   2.260"                  11.0   1,052   20,200 CUP
Hodgdon   H4198   .308"   2.260"               11.2   1,042   18,800 CUP
IMR   IMR 4227   .308"   2.260"                  10.3   1,073   24,500 CUP
Winchester   296   .308"   2.260"                  9.4   1,066   20,100 CUP
Hodgdon   H110   .308"   2.260"                  9.4   1,066   20,100 CUP
Hodgdon   Lil'Gun   .308"   2.260"               8.3   1,047   19,400 CUP

[Rizen 1]

gracious!!!!!

[C.ALLS]

jr460 your reading comprehension skills are about as lacking as your ability to complete a sentence without  a grammatical error. Please read rsterne's post once more and realize he designed this bullet for subsonic use and at no point recommended/suggested it be used at 1500fps. I personally am tired of your post as I feel they add nothing to the thread. This is not because of your lack of understanding of ballistics because it looks as if you have plenty of knowledge in that area but your inability to read rsterne's post and not somehow see something that's not there.

I hope you somehow are able to read back over the post and understand what's actually being posted so that maybe we can learn from what you and rsterne obviously know more about than the rest of us. As of now all I do is read your post and wonder how you managed to put two totally separate facts posted by rsterne together to create something you can disagree with.

[rsterne]

You really need to read what I wrote.... I thought it was quite clear that I was originally working (at the request of Rizen 1) on a 150 gr. bullet at 1500 fps.... The drawing for that is in the other thread.... When I studied it in detail, I realized those velocities were NOT the place to be for wind drift and also realized that we could duplicate the ballistics of a .300 AAC Blackout (200 gr. @ 1050 fps) with a modern PCP.... That is when I suggested the change to a 200 gr. bullet, subsonic, to take advantage of the vastly decreased wind drift.... As stated above....

I started working on optimizing a 200 gr. boattail for subsonic flight, instead of the 150 gr. for supersonic, and the result is shown below....

The rest of that post, below the drawing, talks about the ballistics when subsonic, so I would have thought that clear.... You accused me of changing from a 150 gr. bullet to a 200 gr. because the original wouldn't do what I wanted.... In fact, my view was that the task itself (staying supersonic to 200 yard, starting at about 1500) was flawed, as I showed with this diagram, based the 150 gr. boattail and a flat based version of the same....



The results are quite clear, I bring your attention to the blue lines on the upper graph, which are the 200 yard case that currently interests us.... The solid line is for a boattail and the dotted line is for a flat based bullet.... Whether you agree with the superior ballistics of the boattail or not, you cannot ignore what happens to the wind drift when you stay subsonic instead of going supersonic.... With the 150 gr. flat base bullet, starting at 1500 fps, the wind drift over 200 yards is 6.2 MOA, but starting at 1050 fps it is only 4.4 MOA with a retained velocity of 893 fps.... With the 150 gr. boattail, starting at 1500 fps it is 5.7 MOA, but starting at 1050 fps it is only 3.1 MOA with a retained velocity of 943 fps.... By changing to a 200 gr. at 1030 fps, that is reduced to 1.9 MOA and the retained velocity is 961 fps.... Simply stated, starting at 1030 fps, the 200 gr. ends up faster at 200 yards, and drifts less, than either the 150 gr. boattail or flat base starting at 1050 fps....

I have never made any accuracy claims for this bullet, that would be ludicrous since it hasn't been built yet.... The entire development of the design is based on mathematics, using the formulas developed by Robert McCoy during his work at the Aberdeen Proving Grounds, and tested against real time data there using Chronographs and Doppler Radar to prove the validity of the calculations.... The stated accuracy of the calculations is 3% supersonic (over Mach 1.2), 6% subsonic (below Mach 0.8 ) and 11% transonic (between the two).... The Drag Calculator on the JBM Ballistics website at http://www.jbmballistics.com/cgi-bin/jbmdrag-5.1.cgi uses these calculations to convert dimensions of a bullet into the drag coefficient for velocities from Mach 0.5 to Mach 4.5, with extreme detail between Mach 0.8-1.0 where things change so rapidly.... That is great for airgunners (if we choose to take advantage of it), because that is precisely the velocity range we spend so much time in.... I also use the Drag Calculator by Geoffry Kolbe at http://www.geoffrey-kolbe.com/drag.htm which uses the same mathematical model, and presents it in graphic form, along with the ability to input a muzzle velocity and see the trajectory and wind drift at various ranges....

You may not put much stock in mathematical models, preferring to use your own vast experience to develop your own opinons about what works and what doesn't.... I don't have that experience to draw from, but that gives me the ability to question the status quo, and hopefully further the sport or airgunning by developing exciting new concepts.... I would ask that you be tolerant in your criticism of my approach, and simply let me do my thing.... You may be correct and I may be totally wasting my time.... but maybe.... just maybe.... the projectiles I am suggesting to be suitable for airgunning might end up offering superior ballistics to flat base bullets.... and in my experience, once something is proven to be more efficient.... people will work on the concept until any deficiencies are eliminated....

I'm not trying to reinvent the wheel.... just trying to make it roll easier.... 

Bob

[rsterne]

I have just received word from Veral at LBT that he can, indeed, make a mold for the Whiteout.... However it will require two new patterns, one for the 8* boattail (I knew that) and one for the main body.... The pattern charge will be $200, after which his normal mold prices will apply.... He says he can deliver the mold 2 weeks after payment is received....

Bob

[ezman604]

And I will step in ONE more time to gently remind everyone......let's be respectful with posts on open forum. If you have a disagreement that you feel requires you to attack a post, do it in private message, email, phone call or face to face. But NOT on open forum. If I have to step into another of these type of exchanges, it will get ugly. So, let's keep this informative and enjoyable.
ONLY warning!!!!

We are running a special on free vacations. Will entail a 14 day retreat to begin with.
As a refresher, see Rules #2 and #13.
http://www.gatewaytoairguns.org/GTA/index.php?topic=919.0

[C.ALLS]

I have just received word from Veral at LBT that he can, indeed, make a mold for the Whiteout.... However it will require two new patterns, one for the 8* boattail (I knew that) and one for the main body.... The pattern charge will be $200, after which his normal mold prices will apply.... He says he can deliver the mold 2 weeks after payment is received....

Bob

Being a bore rider I'm assuming he'll need the exact bore dimensions? Should we send him a slug from the barrel after pushing it through the bore?

[rsterne]

A slug would be a good idea.... My concept is for the bore-rider to be 0.001" over the land diameter so that it touches them firmly (0.0005" per side) to guide it perfectly straight.... The driving band could likewise be about 0.001" over, maximum, I don't think it will matter if it is that much over since there is only one to provide friction (and a gas seal).... Veral could easily have a different opinion, and if he is working from a slug, and does his own thing, who am I to argue?.... I would not want to see the bore-riding portion smaller than the land diameter....

The chamber would be shorter than normal, with the leade closer to the breech, because the driving band is further back, of course.... 50% engagement on the lands should be about right, IMO....

Bob

[CHUCKSTER]

Hi Bob,
It is always fascinating to read your theory on new bullet designs...and the ensuing controversy it creates!  I have a question for you to think about...What do you think of the idea of designing airgun bullets to be swaged in a Corbin press, and then instead of having drive bands on the bullets to minimize bore drag, simply run them through a Corbin HCT-2 Bullet Knurling Tool to create a lower bore drag. Do you think a knurled bullet flying sub-sonic would work as well as a bullet with smooth sides? Or do you think it would be more affected by the wind?

I ask because it seems to me that although swaged bullets are far superior to cast bullets due to their greater uniformity in weight and consistency, they cannot have driving bands on them or they would not release from the die. This makes swaged bullets less than ideal for most airguns because there is not enough velocity to overcome the energy robbing drag of a swaged bullet. Which leaves the only obvious alternative which is cast bullets with drive bands...and the inherent drawbacks of trying to control all the variables involved in the casting process.

I just keep wondering if a swaged bullet with a rebated boattail, that is made to be .001 over bore size to seal adequately, and that has been knurled and propelled at sub-sonic speeds would shoot accurately, or if it would be adversely affected by the wind because of the knurling. I also wonder if knurling the bullets would reduce the bore drag to a level acceptable to airgun velocities, or if the drag would still be prohibitive. I wish I had the money to buy a Corbin press, and dies, and a knurling machine, and you to design some bullets for it so I could test the knurled airgun bullet idea.

Just interested in what your thoughts on the subject might be...

Best regards, Chuckster

[rsterne]

Chuckster, one of our own GTA members, Bill G has exactly the setup you are talking about.... He can produce swaged bullets to just over the land diameter and then raise knurled driving bands.... or a single band.... to a precise, and adjustable, diameter.... I have seen some of his prototypes, and feel that he should be able to make this bullet with no problem.... He makes his own dies, and therefore once he has a nose and a boattail die, he can vary the length and therefore the weight.... I sent him an email about this project, but haven't heard back yet....

Bob

[rkr]

Chuckster, one of our own GTA members, Bill G has exactly the setup you are talking about.... He can produce swaged bullets to just over the land diameter and then raise knurled driving bands.... or a single band.... to a precise, and adjustable, diameter.... I have seen some of his prototypes, and feel that he should be able to make this bullet with no problem.... He makes his own dies, and therefore once he has a nose and a boattail die, he can vary the length and therefore the weight.... I sent him an email about this project, but haven't heard back yet....

Bob

Why not use a technique that's available for all of us, cast bullets, sized to land diameter or slightly over and then knurled? Or is there something I'm missing in this thought?

[jr460]

jr460 your reading comprehension skills are about as lacking as your ability to complete a sentence without  a grammatical error. Please read rsterne's post once more and realize he designed this bullet for subsonic use and at no point recommended/suggested it be used at 1500fps. I personally am tired of your post as I feel they add nothing to the thread. This is not because of your lack of understanding of ballistics because it looks as if you have plenty of knowledge in that area but your inability to read rsterne's post and not somehow see something that's not there.

I hope you somehow are able to read back over the post and understand what's actually being posted so that maybe we can learn from what you and rsterne obviously know more about than the rest of us. As of now all I do is read your post and wonder how you managed to put two totally separate facts posted by rsterne together to create something you can disagree with.

Lets connect the dots .
 1 There is no drawing or mention of the same bullet in a flat base version being used to prove the rebated boat tail will do what is being calmed.
2 what rate of twist will be used
3 specifications of barrel; chamber speck, lead speck,lands and groves speck, how many,right hand twist,left hand twist,bore diameter,rifling twist rate, rifling cut,micro grove ,hammer forged or button, air gauged{ MATCH} or standard, LENGTH OF BARREL.
4 at what rpm was this data generated with.
5 How can you have a mould made with out having this data?
6 Most important what lead is this mould being cut for,lead tin,lead tin antimony,lead antimony or pure lead ?
With out these answered the mould and drawing is just a wast of time and money and  just a theory no facts will ever be proven.
Yes I did read THE POST it is just a rambling with no facts to show  how the answer came to be. 
David

[YEMX]

I have just received word from Veral at LBT that he can, indeed, make a mold for the Whiteout.... However it will require two new patterns, one for the 8* boattail (I knew that) and one for the main body.... The pattern charge will be $200, after which his normal mold prices will apply.... He says he can deliver the mold 2 weeks after payment is received....

Bob

This is great news!  Expensive, but great!!  I'll have to email Veral for specifics...

[YEMX]

Why not use a technique that's available for all of us, cast bullets, sized to land diameter or slightly over and then knurled? Or is there something I'm missing in this thought?

Veral at LBT is able to make molds for cast bullets...  Bob is talking about a member that does swagged bullets- just another option over casting is all.

[Pellethuntr]

Why not use a technique that's available for all of us, cast bullets, sized to land diameter or slightly over and then knurled? Or is there something I'm missing in this thought?

Interesting thought, I do not know enough about the effects of knurling on a bullet to comment on how well it would work.

It does seem to me that a mold would be much easier to make if there were no driving bands.

One could very easily make a jig to go between center on a lathe to knurl a few bullets for testing.

[YEMX]

rkr, I think I may have misinterpreted your question... 

[rsterne]

rkr, you are completely correct, the bullet could be cast, or swaged, to just over land diameter and then the knurling process applied to form the drive band(s).... I can't see many guys taking the time or money to set up to knurl, I was merely pointing out that one of our members, Bill G, already has that setup for his swaged bullets.... Perhaps he is on holidays, I can't reach him at the moment....

Most home casters use anywhere from pure lead to 2.5% tin for airgun bullets, to keep the lead as soft as possible.... I personally use 1%, but I have never used a single drive band in a 7" twist, so it is possible that a harder alloy may be needed to stand the higher shearing force from the rifling.... These are the kinds of things that come during the development stage, once the original concept has been proven....

I am reminded of a story about an aerodymanicist who found, in an obscure Russian research journal, the mathematics whereby an object could be rendered nearly invisible to Radar.... He went to his boss, and told him about it, but finished with the statement "the only problem is, the shape is so weird, it can't be made to fly".... His boss asked him how large the radar signature was.... was it the size of an eagle?.... He replied that no, it was about the size of an eagle's eyeball.... His boss simply stated "if it's as good as you say it is, I'll MAKE it fly".... The boss was Kelly Johnson of Lockheed's Skunk Works, and the plane that resulted as the F-117 Stealth Fighter.... That is an example of what can be done through research and refusing to give in to those who say "it cant be done"....

Bob