Published vs. Actual Ballistic Coef.?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Derek M., Jun 5, 2005.

  1. Derek M.

    Derek M. Well-Known Member

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    Seems like a read somewhere here or at longrangehunting last year some threads about true ballistic coef. vs. those published by the bullet manufacturer.

    Will someone please tell me what the TRUE BC is for the following bullets? I'm told BC is variable based on velocity too, but given the same speed per caliber/rifle, I'm trying to establish which of the bullets listed has the highest. Is there an absolute favorite bullet among many of you for your long range hunting? 700-1000 yards?:

    .270:

    140 Nos Accub.
    130 TSX
    150 Nos Btip
    130 Nos Btip
    130 Swift Scirocco

    .30 cal:

    165 Swift Scirocco
    180 Swift Scirocco
    150 S. Scirocco

    168 TSX
    180 TSX
    200 Nos. Accub.
    165 Nos. BTip
    180 Nos. BTip

    7mm:

    150 Swift Scirocco
    160 Nos. Accub.

    I know I listed a lot but someone who has done extensive tests has posted some before, I just cannot remember where.

    Thanks!
     
  2. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Derek M,

    Of the bullets you listed Here are the ones I would say produce the highest BC for a given velocity:

    270

    150 gr Ballistic Tip

    308

    200 gr Accubond

    7mm

    160 gr Accubond

    To get the exact ballistic coefficents, the only best way to get an accurate BC is to put the bullets in the air in your shooting conditions.

    There are better extreme range bullets out there then the ones you listed but of the ones listed I would say these three would produce the highest BC potential.

    Good Shooting!!

    Kirby Allen(50)
     
  3. Derek M.

    Derek M. Well-Known Member

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    Ok, please tell me your favorite long range hunting bullets.
     
  4. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Derek M.

    Not sure this will help you much but here are my favorite long range hunting bullets:

    257
    156 gr ULD RBBT Wildcat BC 0.820

    270
    169.5 gr ULD RBBT Wildcat BC 0.750

    338
    300 gr ULD RBBT Wildcat BC 0.810

    If you want more information on these bullets contact Richard Graves at wildcatbullets@hotmail.com

    By the way, only the 300 gr 338 bullet will work in a standard factory twist. I load my 257 Allen Mag and 270 Allen Mag with the other two bullets to 3365 fps and 3400 fps respectively.

    Good Shooting!!

    Kirby Allen(50)
     
  5. Derek M.

    Derek M. Well-Known Member

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    Wow. Ok, so what twist do I need for the 270 bullets and barrel length? I am getting ready to have 2 more rifles built and am up for suggestions.
     
  6. royinidaho

    royinidaho Writers Guild

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    Been shooting a 270 Win with 140 gr Hornafdy and 130 Nosler ballistic tips. Don't know what actual vs published BCs are. After developing a drop chart (actual shooting every hundred yds out to 500 yds) it doesn't make any difference.

    Was busting 1 gallon milk jugs at 650 yds on a regular basis.

    Richard Graves sent me some prototype 168 gr RBBTs just to see if they will stabilize at Win velocities and 10" twist. (Just a fun experiment). They sure a good looking suckers. Way too heavy for the 270 Win even though I have a 27" Lilja bbl. Velocity won't be much. Now if it were a 270 Allen Magnum it would be the 220 Swift of the larger cal world.
     
  7. Derek M.

    Derek M. Well-Known Member

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    What is a 270 Allen Mag? What is it "close" to with respect to comparison? Is it a necked down big magnum?
     
  8. 7Rumloader

    7Rumloader Well-Known Member

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    I'm not Kirby but I can help here. Read this and it will give you a lot of the info you desire on the Allen Mags and the rest you can get from Kirby aka fiftydriver via email at kballen@3rivers.net .
    He is a wonderfull guy to talk with and a hell of a gunsmith!!

    I apologize Kirby if I jumped the "gun" in giving a little info out for you. /ubbthreads/images/graemlins/frown.gif
     
  9. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Derek M.

    The 169.5 gr ULD Wildcat will require a 1-8 twist to be stabilized in any round especially the 270 Win and 270 Wby class.

    I agree with Roy in Idaho that this bullet is to large for the 270 Win except for use as strictly a paper puncher at long range. In the 270 Wby class you start to get enough velocity to ensure expansion at some decent ranges.

    Jump up to the 270 STW class round and it really starts to come into its own as youcan get into the 3100 to 3200 fps range with top loads.

    [​IMG]

    This is a pic comparing the 130 gr Ballistic Tip to the 169.5 gr ULD RBBT Wildcat Bullets.

    [​IMG]

    This pic compares the 270 Win(130 gr Ballistic Tip) on the left, 270 Allen Mag(169.5 gr ULD) middle and 7mm Rem Mag(140 gr Ballistic Silvertip) right.

    Velocity performance of the three are as follows:

    270 Win.........3100 fps w/ 130 gr BT
    270 Allen Mag...3400 fps w/ 169.5 gr ULD
    7mm Rem Mag.....3350 fps w/ 140 gr BST

    Comparing apples to apples, the 270 Allen Mag will easily top 3850 fps with a 130 gr Ballistic Tip. Of course this is out of a 30" barrel but even given equal barrel lengths the Allen Mag will top the Win by +600 fps easily.

    The 270 Allen Mag is based on a full length 7mm RUM case with the shoulder angle increased and body taper reduced to a very minimum. Case capacity of the 7mm RUM filled to the mouth with 8700 ball powder is 117 gr compared to 126 gr for the 270 Allen Mag.

    The 270 Allen Mag capacity is slightly more then the 7.21 Firebird from Lazzeroni but it is able to be easily chambered in rifles such as the Rem 700 where as the Firebird is more difficult to squeeze into this size of receiver. It can certainly be done but at more expense then the 270 Allen Mag.

    Cases are easy to form, run 7mm RUM cases through a 270 Allen Mag FL sizing die, prime, load, fireform, trim to length and your ready for serious performance.

    The Allen Magnum rounds were designed for chambering in my Extreme Sporter rifles with barrel length of 28 to 30" and finished rifle weights ranging from 8.5 lbs to 11 lbs. They are also at home in heavier rifles as well but the goal was to offer the extreme in performance in a portable package and they have performed very well at that.

    Good Shooting!!

    Kirby Allen(50)
     
  10. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    7RUMloader,

    Go ahead and give out all the information you want on the rounds. You really do need to burn that 7mm RUM barrel out though so we can fit a new turbocharged 270 barrel to that receiver /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/grin.gif!!

    Good Shooting!!

    Kirby Allen(50)
     
  11. Derek M.

    Derek M. Well-Known Member

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    SOLD!! How fast can you build me a rifle? I want a 270 Allen Mag. What does ULD RBBT stand for?

    What rifle action would I need to send you to fit that caliber? I can go to Bass PRO Shops here and buy a 300 or 7mm RUM. I'm assuming that is the size bolt face since you use that brass. I will email you. By the way, seems like I've seen your handle over on AR.
     
  12. Derek M.

    Derek M. Well-Known Member

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    Oh yes, and how about throat erosion? Is this round considered overbore? I never let my rifles get hot or even real warm so usually I'm not worried about stuff like that.
     
  13. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Derek M.,

    Drop me an e-mail at kballen@3rivers.net and I will get you back the specifics you need as far as pricing and options on these rifles and we can discuss the details more to get you the exact rifle you want to cover your goals the best.

    These are very large capacity rounds so of couse they are harder on barrels then smaller capacity rounds will be.

    That said, if you use the 169.5 gr ULD RBBT I would recommend you getting ahold of Jeff Bartlett at www.gibrass.com and order in some WC872 powder. This is GREAT powder for the 270 Allen Mag with the +150 gr bullet weights.

    The nice thing is Jeff is a great guy to deal with, he sells very quality powder and the best thing, 8 lb kegs run $40 each!!!

    IF you buy 4 kegs the Haz shipping charge is only $5. If you buy 6 keps there is no Haz shipping. I ordered in 32 lbs of the same lot of WC872 for testing in my 257, 6.5, 270 and 7mm Allen Mag and the total cost was $188 including all shipping charges.

    Thats breaks down to about $5.80 per lb of powder!!!

    There are also other advantages to this powder over stick powders other then cost. It burns much cooler then modern high energy stick powders. This translates into lower bore temps which means longer barrel and throat life.

    Also, being a ball powder, it is very gental to the throat of your chamber as the powder is forced through the throat under high pressure and heat. This can significantly increase throat life.

    Knowing these round would be hard on throats from the start I designed, or should I say, I had Dan Lilja design barrels and twist rates specifically for these extreme performance rounds. For the 270 Allen Mag, I had Dan tool up to build 1-8 twist barrels in his great 3 groove rifling design. This system works great with big game bullets and offer extreme accuracy with high velocity and very copper fouling.

    They also limit throat errosion longer then a conventional 5 or 6 groove rifling design. They are not the best system for a thin jacketed match bullet but then again at the velocity potential that the Allen Mags produce, there is no point in using the thin jacketed match bullets because more then likely they will not survive the launch speeds anyway.

    The Allen Magnum chambered Extreme Sporters are a total system designed to offer the highest possible performance with the longest accuracy life potential in the rifle.

    Throat life with these rounds used in the correct way and taken care of like you do correctly will easily be in the 1300 round range at least. With the 270 Allen Mag, it may well reach 1500 rounds with 3/4 moa accuracy which is still plenty for long range hunting potential.

    These rounds are designed for big game hunting and as such, a 1300 round barrel life will last several lifetimes for even serious big game hunters.

    Drop me an e-mail and we can talk specifics on what type of rifle you want.

    To answer your questions, ULD RBBT stands for Ultra Low Drag Rebated Boattail.

    The Rem 700 in any of the RUM rounds will be the absolute perfect receiver for the 270 Allen Mag rounds. No receiver modifications needed at all except to accurize to get them shooting under 1/2 moa!

    Drop me a line and we can start the process.

    Yes I used to post alot over on AR. Got into a few pissing matches with guys that did not feel logn range shooting was ethically possible so I came over here to be around like minded shooters and hunters that know full well what is totally ethically possible.

    Just a matter of having the proper equipment and the ability to use it properly and more importantly, know when you should not use it!

    Good Shooting!!

    Kirby Allen(50)
     
  14. Derek M.

    Derek M. Well-Known Member

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    I sent email 2 seconds after my last post. Also, and please don't take offense to this because it is certainly not meant that way, but, how do your Allen Mags compare to the 7mmSTW conversion that John Burns designed? When I say compare, I do not mean whos is "better." Rather, I would just like to know ballistics comparisons I guess.

    I'm certainly also not opposed to a 7mm Allen Mag either, and I'd like to know how that compares to a 7 RUM.

    Seems like I saw a 300 RUM at Bass Pro in left hand (BDL 700) on sale for $425. Too bad it's not stainless.

    What action do you like better, the Remmy or Savage?