Boosting BC of commerical bullets.....

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Fiftydriver, Mar 17, 2013.

  1. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Well, this is an idea that popped into my head several years ago when I was working with the old Wildcat Bullet company. My work load grew to the point that I really just put it on the backburner until I found out that Corbin started selling these aluminum tips. That really got the ball rolling.

    Well, Over the past several weeks, I have machined up several collet fixtures to allow me to precisely mount bullets in my lathe at the shop and do the needed work to convert them for these tips in a precise and repeatable manner.

    Was able to take a couple hours this afternoon and put all the theory into reality. The main reason for wanting to try this is mainly the fact that the 375 cal, 350 gr SMK bullet is really a pretty poor performer as far as expansion at long range. The reason is because its jacket is massively thick. I figured one of these aluminum tips would not only boost BC but it would also make BC more consistant and aid in expansion at long range. Anyway, just starting out working on this but the theory worked very well and here are some examples.

    [​IMG]

    Both of these are 375 cal, 350 gr SMK bullets, one on left modified for the aluminum tip. This added 0.137" to the OAL of the 350 gr SMK and should make a significant boost in BC as well as expansion performance at long range.

    [​IMG]

    This one also intereted me. I have always liked the Nosler Accubond but they tend to run a bit low in BC, especially in 375 cal. This is the 300 gr Accubond in 375 caliber. Modifying this bullet for the aluminum tip added nearly 0.200" in bullet length. This bonded core bullet with a much better BC will make it a viable option for the larger 375 magnums for long range use including in my 375 Allen Magnum loaded to +3400 fps.

    [​IMG]

    Perhaps the one that interests me the most is the Barnes 375 cal 300 gr TSX. By modifying this bullet with the aluminum tip, it gains a massive 0.333" in OAL. The BC increase for this bullet should be huge by removing the massive meplat of the standard bullet. Plus, Barnes bullets tend to be poor expanders at true long range distances, this tip may eliminate that issue.

    Next up I tried a couple 338 caliber bullets.

    [​IMG]

    Here is the old war horse, the 338 cal, 300 gr SMK. Adding the aluminum top took the OAL of this bullet from 1.720" up to 1.840" and should help to boost BC a bit and also make BC more consistant from shot to shot. Expansion has never been a HUGE issue with this bullet in the larger magnums but this tip may allow the smaller 338 magnums to get better performance at that +1000 range.

    [​IMG]

    Another Barnes bullet that really impressed me. The 285 gr, 338 cal TSX-TAC. This one modified with the aluminum tip made it the longest bullet made of all the ones I tried so far. The tip added 0.165" to the standard bullet with an OAL of 1.962" making this one, one of the more interesting ones for me to test at long range out of my 338 Allen Magnum loaded to 3400 fps or a bit more. Again, should get a good boost in BC as well as better expansion at +1000 yard ranges.

    These were the first bullets I have made so far with my new collet system. Again, these bullets are machined to accept these tips, not swaged formed. I will be working on the following bullets as well to see what improvements can be made on them ballistically:

    6.5mm
    123 gr SMK
    142 gr SMK
    130 gr Accubond
    140 gr Accubond

    7mm
    160 gr Accubond
    175 gr SMK
    180 gr SMK

    30 cal
    180 gr Accubond
    200 gr Accubond
    210 gr SMK
    220 gr SMK
    240 gr SMK

    I will also be working on some Barnes bullets in all of these calibers as well to see what they can turn out. You may notice that there are no berger bullets listed. The reason why is because their ogive design is a bit more aggressive then the ogive on these tips. The result would likely be a wash in BC with the smaller ogive but slightly blunter meplat. I may test them. The 300 gr Hybrid may benefit from a tip as far as expansion at long range from chamberings such as the 338 Edge, 338 Lapua an even my 338 AX where there have been some examples of pencil holing through big game at ranges past 1000 yards. This tip would certainly solve that problem.

    Again, just starting, no bullets in the air yet. I have made up 25 of each of the above bullets for testing. When that will happen, not sure. Still lots of customer project rifles to get out the door but hopefully with spring here and longer evening day light hours, I can spend some after hours time on the range doing some more ballistic testing.

    I am also going to test these tips in the Barnes TSX bullets in 416, 458 and 50 caliber. The tips used in these larger calibers will be a much larger tip design.

    Should be interesting, stay tuned. It can be scary what a curious mind and a precision metal lathe can produce with a few sleepless nights!!! :D
     
  2. screech

    screech Well-Known Member

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    Should be interesting. How are you attaching them
     

  3. bigbuck

    bigbuck Well-Known Member

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    Those things look Awesome ! Meat Darts:D
     
  4. barnesuser28

    barnesuser28 Well-Known Member

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    those are pretty cool, they look similar to elkaholic's bullets.gun)
    would you ever sell these to people who dont have a lathe? namely me?:D:D
     
  5. Engineering101

    Engineering101 Well-Known Member

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    Kirby

    I’m impressed that you could make such a mod to so many different bullets without tearing them up let alone have them turn out looking like factory new. It will be interesting to hear what you discover when testing them.

    Are not the 30 cal and under bullets you mentioned a little less interesting given that Nosler is coming out with their Accubond Long Range line?
     
  6. royinidaho

    royinidaho Writers Guild

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    Kirby,

    You and I seem to be a lot alike when it comes to getting all of the bc possible,

    The differences between you and I are that you have skill, experience, talent, equipment and an uncanny knack for bringing these together with near magical results. However, I do think that I have it on you in the 'looks' area. :D:D

    I knew nothing about machining. Still don't. But have learned a tone making buckets and buckets if chips. Both aluminum and brass.

    I bought me a HF 8x14 bench lathe and ruined a set of jaws getting +/- 0.00001 run out. But I got zero runout. Good start.:rolleyes:

    Objective was to get bullets worthy of use in one of your 270 AMs.

    First attempt was to stage 7MM Berger's to .277. Corbin made me a die. He said that it was too much swage but to know I'd have to try. I tried. It didn't work. Typical for me.

    Running Dan Lilja's bc spread sheet said thar simply increasing length without increasing weight wouldn't get me a significant bc increase.

    That's when I got the lathe and came up with a tip design to fit the 270 NAB and Ballistic tip. I chips quite a few feet if brass rod before converting the lathe to CNC to get some thru put. used LEGOs Mindstorms components for then CNC. Laugh if you wish. But it worked. :D

    Tips were well within my very tight specs. However without an automatic feed, even w/CNC it was too slow to pencil out.

    A commercial bit was $15,000.00 minimum order. Well out of reach to get a $0.15 Point.

    Kevin Cram made up a very well working meplat trimmer which allowed a very straight face for the tip to butt against and a uniform length which was critical for proper seating of the tip.

    Eaglet's computer calcs said the bc was increased from 0.497 to probably 0.658. Significant! Never got to confirm.

    Bullet weight increased from 150 to nearly 160 grains. Length of the tipped 150 NBT/NAB was right there with Richard's 195 WC.

    End result was thar re-tipped Noslers shot along with the originals which is very well in this rifle.

    The down side was that less than 20% of the tips passed my quality control. :rolleyes:

    I've come up with several hundred of Richard's originals, 150Bergers shoot very well in this barrel and Berger announced imminent release of a 170 gr offering which pretty much quenched my motivation.

    Reason for the low QC results was flexing of the 3/16" brass rod. The steady rest was almost 1" from the chuck jaws which, unless I had the cutter ground exactly correct and took very small cuts there was a very small flex in the rod. This flex was hard to detect but raised its ugly head at the 200 yard target.

    I think I ran out of persistence with the 277 project.

    I do have that 375 AM which sucks me back in this realm. I went with the 375 vs the 338 with the thought that one day there would be a bullet that would raise 375 AM performance to its proper position ABOVE its little brother. The 338 AM. :D
     
  7. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    They are press fit and WILL NOT come out.
     
  8. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Can not say right now, at the moment, just playing around to see what CAN be done and how well it can be done. Once I prove things, MAYBE.....
     
  9. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Its really a pretty simple set up, the tricky thing is to figure out how much of the ogive needs to be removed and then getting a system that is repeatable. Not every bullet is perfect, still working on a few tweaks but it does pretty well.

    If Nosler stays on pace with past bullet releases, we should see the new bullets sometime around 2015!!!:rolleyes: Anyway, they had a huge opportunity to make a perfect long range big game bullet in their 300 gr, 338 cal accubond and they flubbed that badly. Not saying its a bad bullet, its accurate and terminally it is great but the baring surface is WAY to long which reduces top velocity potential in any chambering and the ogive design is no different then any of their other ogives and it should have been much more aggressive. They could have easily made a .800 BC bonded core, tipped bullet, unfortunately, they played it VERY safe and came up with a .700 BC bullet that is 50-75 fps slower then the SMK and 75-100 fps slower then the Berger of the same weight. FLUB!!!! I will believe their new LONG RANGE Accubonds will do what they say when I put them in the air and they match up to the computer models, until then, I will not hold my breath.

    I am not flaming Nosler in any way, I love their Accubonds, they just could be made more aggressively and still easily be stabilized by standard twist rates which for some reason is something that they just do not believe. Not sure why.
     
  10. barnesuser28

    barnesuser28 Well-Known Member

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    If you do i would be very interested in a 280 grain Barnes LRX with the metal tip, i think the BC would then be very close to that of the 300 SMK or maybe even a little more. Take care.
     
  11. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Roy,

    I am working on or will be working on some 270 bullets as well, the 150 gr Barnes tsx should show some promise in spite of being a flat base bullet. In spite of conventional wisdom, a flat base bullet will actually fly to 1000 yards and well beyond.

    Driven out of my 270 Allen Magnum it will clip along at a solid 3500-3600 fps depending on barrel length used.

    Its listed with a BC just shy of .5. With one of these tips, I would think it would crowd .6 BC pretty hard. A .6 BC bullet at 3550 fps is not to damn bad!!!

    The sierra 150 gr SPBT Gameking would also be a other great choice offering around .6 BC in finished tipped bullet but I am afraid that at the velocity potential of the 270 AM, it would pop like a big Blitzking on big game and really make a mess and not penetrate very well.

    The 140 gr Accubond will certainly be tested as well. IF Noslers new 150 gr LR accubond actually gets here and actually has a BC of .625, it will bring new life into the 270 AM but you can wish in one hand and crap in the other and see which fills up first. I think you know what I mean with that mental image!!
     
  12. Engineering101

    Engineering101 Well-Known Member

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    Kirby,

    Any idea what Nosler has done to get their LR bullets to perform all the way down to 1,300 fps? They must have changed the core material, no?
     
  13. HARPERC

    HARPERC Well-Known Member

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    Roy nailed it, main difference being I didn't have my looks to fall back on, when my skill level proved insufficient to the task. Very cool to see it done.
     
  14. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Not nessesarily, the core they use is very soft anyway. If I had to guess, I would say they did a couple things other then change the core alloy.

    1. More aggressive wedge design on the tip and also a deeper hollow cavity under the tip to allow freeer expansion at impact.

    2. Redesign the jacket for a thinner jacket at the meplat and ogive.

    Now, this is just speculation and nothing more but if someone asked how to get better expansion at longer range, these two ways would do it.

    Their cores are noticably softer lead then a SMK for example.