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New bullet maker that looks interesting

 
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  #15  
Old 05-21-2014, 04:12 PM
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Re: New bullet maker that looks interesting

Couple things come to mind. Length does not always dictate an increase in BC. Think 6.5mm -130grn Berger VS 130grn CEB. The CEB is the same length as the 140 Berger with only a marginal increase in BC over the 130 Berger. .550 vs .560 respectively (IIRC) with an oal increase of ~.021".

The BC calculated by the manufacturer is most likely static in nature, fired from a single rifle at a single velocity at similar air density. As the testing becomes more dynamic, with changes in velocity & air density one will most likely see a (possibly dramatic) change in ballistic coefficient.

I'm not guru or SME on these things, I only know enough to get myself in trouble My statements on BC are just what i've experienced personally.


t
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  #16  
Old 05-22-2014, 02:28 AM
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Re: New bullet maker that looks interesting

Let me be the first to call bs on those BC numbers. Unless these are physics defying supernatural bullets. I am of the opinion that it is nearly impossible to ever see a 175 grain 30 cal bullet over .550 G1 or a 155 grain 30 cal over .490. Advertised yes. Real world no.

It is very often misunderstood that length in and of itself equates to higher BCs.
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  #17  
Old 05-22-2014, 12:47 PM
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Re: New bullet maker that looks interesting

Michael Eichele

Thanks for responding to this thread. i have only personal experience to contribute and that is BC's posted do not equal BC's tested by me.

For a flat base to have a high BC would require a very gently and long tapered nose. So I have the following questions:

1) Tapered long nose = unsupported. Bore diameter short base = supported. Long unsupported nose launched into the rifling guided by a (very) short base. Without a sabot to keep the nose centered, what are the odds of the nose NOT entering the rifling cocked off center?

2) If the bullet exits the muzzle cocked from launch, how far down range before it "goes to sleep"?

3) Is there an increased probability that the bullet which has an unstable form tumbles or disperses from intended LOF? My understanding of aerodynamics is that cone shapes are stable only at subsonic speeds. The supersonic shock cone allows a tapered body to cock sideways until it's surface intersects the shock cone and sets up a battering oscillation inside the cone. Bullets have to be spin stabilized to stay point on above 1120fps. Unless I'm all washed up about this....

4) Since conventional boat tail construction somewhat balances (centrifugally) the bearing surface on opposite ends by boat tail and nose, does this new bullet have a deeper BT to offset the longer taper of the nose?

If somebody could please design a 55 grain SpFB 22 cal. bullet with a G1 BC = or > 1.0 I would appreciate it!!! I'll be the tall bald guy at the front of the line.....

KB
  #18  
Old 05-23-2014, 03:21 AM
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Re: New bullet maker that looks interesting

Robert McCoy writes that a ~7 .7 cal boattail is about ideal.
About 60-70% of all supersonic drag is created at the base of the bullet.

F=P*A
A boat tail reduces the area at the base of a bullet so that the lower than average air prassure behind the bullet "pulls it back" with less force.
If you choose a taper too shallow, you have more area than necessary, the negative pressure can work on, if your taper is too big, the negative pressure can actuate more force on the tapered surface which creates a greater force in sum, despite the smaller base area.
At ~7 .7cal length there is an ideal equilibrium between taper and base area that allows a minimum of base drag.
Of cause this is only true for straight tapered boat tailed designs, there may be other geometric shapes even better suited. Rebated boat tails though, aren't as far as i've read. Bryan Litz e.g. was pretty clear on that afair.

So advertising a flat base bullet with much better form factors than common boat tailed designs, is more than a bit bold.
  #19  
Old 05-23-2014, 11:43 AM
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Re: New bullet maker that looks interesting

elkaholic has been building some bullets very similar to these RBT bullets. I obtained a velocity-based G7 BC of 0.286 for elkaholic's 190gr .308 SXR bullet from my 300 Win Mag. I recorded bullet velocity at the muzzle and then again at 1000 yds.

W3PS is advertising an equal BC value for their 155 grain TAC-PM™ RBT. Their 155gr bullet weighs 35gr less, and is much shorter in length.

W3PS has left Nosler in the dust with these promotional-based BC values. After all, it works for Nosler. Velocity-based BCs will tell a different story.
  #20  
Old 05-23-2014, 09:42 PM
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Re: New bullet maker that looks interesting

I can guarantee you that those b.c.'s are GREATLY exagerated! No matter how much we would like to think otherwise, there are laws of physics that apply.......Rich
  #21  
Old 05-24-2014, 05:24 AM
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Re: New bullet maker that looks interesting

What I want to know is .... are the 230 gr .30 cal bullets a new proprietaty design or are they simply modified & re-branded Berger bullets ?
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