an interesting test: BT vs FB

G

GLF

Guest
this afternoon , me and my shooting pal were at ours range practicing for the incoming Super Shoot.
as usual i was shooting my Bart's Ultra 66gr , Quaglino was shooting his own 68gr BT: both charge with lot 12806-2006 n133, my jones set is 54 1/2 clk ( 29.9 gr) and he set at 55.0 ( 30.5 clk).
after a wile, fighting with a trichy wind , a tunderstorm were around us, and shoot some good groups, we'll take out the cronoigraph, just to see thew vel of ours tune.
here the surprice: hes average speed was 3445 , mine 3500. as i was using 66 vs 68, my .6 grs of difference it looks true. both with a 2.5x SD.
then we take the cronograph at 100 mt, just in front of the target.

gosh... my .050 fps advantage is gone .... mmmm

we loose , quaglino's BT 327 fps per 100 mt , 377 fps the ultra's 66.

so, the better CB of the BT HAS an advantage over the FB?
the groups shoot are all nice , ranging from .120 to low two's.

any tought around here? anybody has made a similar comparision?

just to know...

Gian Frizza
 
Gian,


My thought is that while at 100 you two were similar.............think about 200, or even 300! THEN the BT's will shine.....


Quag "passed you up" at about 75-80M!!!!!!


:)


al
 
Gian

In theory, the BT does have a slight BC advantage, depending on the design. I am surprised it showed up at 100 yards. But then, I have never set a Chrono up at 100 to see. Interesting findings.........jackie
 
By checking speed at the muzzle, and speed at 100 "yards" or meters, you are comparing the loss of speed over the distance to be tested. That test is showing you the Ballistic Coefficient in a round about way. BC does not however show you which bullet is more accurate, just which one gets to the target with less loss in time of flight. A flat base with a lower BC that leaves the barrel faster than a BT with higher BC just may have less time of flight, but if muzzle velocity starts the same and bullet weight is the same, the better BC bullet will get to the target sooner and be less affected by wind. For short range BR, I just stick with the most accurate bullet that I can GET. Some bullet makers make great bullets but if you can't keep them on hand what good are they. The bullets I use, I have been able to keep on hand and the guys aren't hard to deal with. They are also very accurately made bullets, and work with well with the design of our chambers.

Paul
 
Jackie
nighter us nevr try this before, but today, during the cleaning section, we'll go into the subject who's better? BT or FB? something like's befor was the egg or the chicken?
in future, we'll try with cronos set at 10ft from muzzel, 100 and 200 just to see the loss of vel at combined distances.

Al, nice to listen from u, are u coming to the SS this year?
my idea is to go unto Bart's Bt soon...... hehe not givin' Quag to pass me up... :rolleyes:

ps: a statistic manner: the groups looks the same

Gian
 
Similiar tests, yup

A fellow shooter and I got together and spent a whole day with
two chronographs. One was set at 10 ft, the other was set in front of the
target at two hundred. The purpose was not specifically to test Bt
advantage, but rather to test for loss of Vel on a bullet I was making
that had a large hollowpoint. We did test Bt and it was true, they crossed the line faster. It was not by a lot.
Five cases were used all day and 5 shots with each bullet were
fired, with weighed charges. The terminal Vel was subtracted from
the muzzle Vel and each shot was recorded, then averaged. The only Bt's
I had on hand were Brian Rubrights and sierra 70's. Other bullets
were Mine, Bill Brawands, Eubers, Estes and Myles Holister's
My bullets with the big hollow point were in fact the slowest.
The Bt's were faster, but not what I had thought. With a Muzzle Vel
of 3200, the loss for BT's averaged 599ft per sec for Brian Rubrights
Sierra 70's were right behind at 610. The other FB lost about
630 and mine with the big nose lost 665. From that I decided to
find a new address for that die. I don't however consider 20
or 30 ft per sec. enough advantage to shoot a BT over another
FB which shows dependability and gives me confidence.
The most interesting thing I found, was that in each shot. If
it left the bbl faster, it also slowed , or lost slightly more speed.
I assume that to be additional air drag caused by the higher speed.
Another consideration is that both chronographs were oehler
33's and if both were in good order, they still have a possible error
of 1 percent. The ES was actually very good and I was pleased
with the results. I might find the actual paper if I look hard, it was
20 years ago
 
Bib Kingsbury,


Thank you for testing and sharing the info. I find this statement to really encapsulate or SUM UP a glaring FACT of ballistics................"You can't solve wind problems by going faster".

Quote >>> " The most interesting thing I found, was that in each shot. If
it left the bbl faster, it also slowed , or lost slightly more speed.
I assume that to be additional air drag caused by the higher speed." <<< unquote


"Wind drift" is a DRAG function, not a function of the wind blowing the bullet over. The increased DRAG that you observed will also be responsible for increased WIND DRIFT. The bullet which loses more speed will be dragged over further by the effect of the wind (Not BY the wind, but by the EFFECT of the wind......the wind re-directs the drag so that it is dragged down-wind)


No Gian I won't make the SS. Thank you for asking.


al
 
Al,

Reading your comment it sounds like you are saying that the faster a given bullet is fired the more velocity it will lose (of course that is true) due to the greater drag which in turn causes more drift.

I assume you don't actually mean the faster bullet will drift more than a slower one ?

Is it correct that the faster bullet has a greater drag operating on it but because it's average velocity is still higher the drag operates over a shorter time frame and as such the actual wind drift is less. Isn't the drift a function of the total drag and the time the drag acts with the only place that a faster bullet can drift more than the same bullet going a bit slower is right around the speed of sound where the drag takes a big jump and the extra drag becomes dominant over the lower flight time.

For a typical 68 grain PPC benchrest bullet wont 3400fps will always drift slightly less than 3200fps.

??????

Bryce
 
Last edited by a moderator:
Bryce,

You are correct.

What I was pointing out is that the law of diminishing returns is in full effect, the advantage of the 200fps is VERY nearly canceled by the added rate of loss and going to a lighter/faster bullet with the intent being to "lessen wind drift by getting the bullet there faster" is most often a mistake UNLESS the lighter bullet is inherently much more accurate.



al
 
The ES was less at 200 than at the muzzle, that was clear. We should have looked at that and played with the numbers more than we did. Assuming
a 3400 fps load looses about 25 fps more than a 3200 the advantage is
175 at 200. That sounds like a lot, but is in reality a rate of speed. What
is the true gain in a given wind of say 20mph ? What would be the difference in time of flight?
 
Bob,

Was the extreme spread lower in terms of actual velocity or still lower as a percentage of the velocity ?

What I mean is that the muzzle velocity is higher so the spread will also be greater, at 200 the velocity is lower so the spread will be less. If expressed as a percentage of the velocity they "should ??" be the same.

Example: If a bullet starts off at 4000fps with a spread of 40fps and at some distance out has slowed to 3000fps with a spread of 30fps that is the same relative percentage velocity spread.

Bryce
 
Bryce, I have not found the paper with numbers yet, so can only say this
example only: a shot fired at 3225 lost 640 and a shot fired at 3200
lost 610 , so the slower round lost less than the faster. this is for each shot
fired, not the average
 
Bryce,

I know that you already know this but for those folks just tuning in :) ........An easy way to picture this is that the "rate of loss" IS DRAG...........so a bullet that loses more velocity or has a higher "rate of loss" is exhibiting MORE DRAG and "wind drift" is purely a function of drag /time of flight, all the wind does is move it around to the downwind side of the trajectory which "sucks" it off line. The bullet which slows down less exhibits less wind drift. If the bullet didn't slow down it would exhibit nearly zero wind drift.


this is not meant to be a comment on your question re ES.


al
 
So Al,
If I shoot the same bullet from the same rifle, one time with a load that is faster, the other with a load that is slower, you are saying that the one with the higher MV will have more wind drift at a given distance, with equal wind conditions for both shots?
 
No, I'm not being clear. :eek:

The increased velocity will over-ride the increased drag (drag over TOF) but you will get a smaller return than would seem "logical". You get back less than you put in.

And in the case of going to a smaller but much faster bullet, like dropping from a 68 down to a 55gr 6MM bullet to get 300-400fps the increased drag will in fact increase the wind drift.

I'm attempting to illustrate WHY a light bullet starting at 4000fps will be blown over more than a heavy bullet in the same caliber that's only launching at 3000fps. That it's not just time of flight but LOSS OF VELOCITY over time of flight. A very fast bullet may get to the target in one second while a slow bullet may take 2 seconds but the slower bullet will nearly always be "blown over" less.

In the case of a round ball it's so close to a wash that some feel that upping the velocity actually DOES increase wind drift but for typical BR bullets with a BC of around .25 the added velocity will always decrease actual wind drift. A little ;)


Bryce's question is a good one because if ES is NON-linear with drag loss then it would be logical to chase the more consistent ES over the wind drift difference. If you're shooting a long way and being blown over a matter of inches then the difference between your group center being pushed 3.1" VS 3.2" is meaningless as long as it's consistent. It's the DIFFERENCES that'll eat you, not the total amount that the group is moving over.


This being the centerfire forum I'm really preaching to the choir but I take every opportunity to illustrate that speed isn't everything. There are a lot of shooters who read here who are still convinced that shooting "flatter" offers some advantage.


One place where this is relevant to short-range BR is related to the perception that a 3600fps .22 offers an advantage over a 3400fps 6PPC. This is true ONLY if the smaller .22 bullet has a similar BC as well as similar accuracy. If the smaller .22 bullet starts out fast but slows down a bunch more than it'll be blown over more than the 6PPC bullet. And if it's blown over more, then it'll also be more affected by pickups and letoffs, it'll be less forgiving.


BUT, same bullet pushed faster will have less wind drift. period. Not LOTS less, but less. Faster with the same bullet IS BETTER all else being equal.


Except for subsonic .22's............if they go fast enough to enter transsonic or go super than the wind drift will spike, the faster bullet WILL be blown over more. Or so I hear. ;)


al
 
Interesting test. :)

At the risk of being a wet blanket ;), here's a few things to keep in mind:

3200-610= 2590
3225-640= 2585
----------------------------------------------------
Most chronographs have a 1% error factor
----------------------------------------------------
Technically, it's wind deflection not wind drift.
----------------------------------------------------

I'm going to try this next time I do some chrono work. Good shootin' -Al
 
Al,

Wouldn't it be "wind induced drift" ? Maybe "wind induced suck" !! Wind drift sure does suck !!

I am sure you know this Al but for others that may not, I know I scratched my head how this worked for years until Alinwa schooled me up right here on this site.

Wind tips the spinning bullet so it's nose points INTO the wind so bullet is flying at a slight angle so long as the wind holds. Bullets base drag now acts at that same slight angle so the base drag has a rearward and horizontal component. The rearward component slows the bullet down and the horizontal component SUCKS the bullet sideways. It is that sucking sideways that moves the bullet in the wind.


Boyd, again I am sure you know this but as an extra to Al's comments. Total wind drift is a function of the drag and of the time of flight. If the velocity is higher for a given bullet the time of flight is less but the drag is higher. The lower time of flight drops the drift and the extra drag increase the drift. The net result will always be less drift since the time of flight will overcompensate the extra drag. The thing is the difference isn't great. Intuitively 3400fps vs 3000fps for the same bullet seems like a big gain bit the wind drift will not be a great deal less for the faster bullet.

The same sort of effect that happens with cars and speed. Say it takes 500 horespower to go 200mph, it will probably take something like 1000 horespower to go 250mph. Just numbers picked randomly but you get the point. You put a lot more work in to overcome the extra drag. I am guessing that drag is something like a squared or a cubed function of speed. Go twice as fast and get 4 times (or more) drag.

Bryce
 
Guys,
My question did precisely what I wanted it to.:D I just have one more question; how do you turn a round ball into the wind?
 
Last edited:
:D


'E's a snarky barstid I tells ya'....

The "turning into the wind" is an effect, an ARTIFACT, a side-issue if you will, not the cause of wind-induced-drift or deflection. Turning into the center of the airstream is what the pointed bullet HAS TO DO to keep from tipping over, this means that its base drag is off to the side of its trajectory. It doesn't CAUSE the base drag to be there, it's just where the base drag IS, in the lee of the wind.


The CAUSE of windrift is the pocket of low pressure behind the bullet which is acting to slow the bullet down.......the wind just makes the bullet think it's going where it's not, the pocket of drag is always in the lee of the bullet no matter what it's shape. The wind only causes the "back" of the bullet (opposite the center of the airflow) to be moved slightly off center REGARDLESS OF THE BULLET'S SHAPE :D

Suck-back becomes suck-back-a-little-sideways ;)


Now.......to compound the issue, a true sphere WILL NOT turn its axis of rotation to center on the wind. It can't. Shoot a round ball through a tight twist and it'll almost circle round to hit you in the ear.......



Now al(nyhus)innodak,


IF the data are accurate then we may have an actual example here of a transitional zone where a variable BC actually DID act to give the faster bullet more deflection. No wet blanket A'tall, I think that's where Bryce is heading to too.


ta ta



al(notnyhus)inwa
 
Last edited:
Al,
I'm proud of ye. This is a more rational and articulate explanation than graced our previous thread on the subject. Things seem to have evolved and refined in a good way. Now if you guys will think a little farther, you will see that the bullet does not create a new airflow direction, but is influenced by the sum of the effects of the forces acting on it. That sum creates an effect that is the same as if a single force was acting in the direction and magnitude that a resultant vector (component of a method of graphic solution of a force problem) would represent, but the actual forces are unchanged. Sometimes folks look at a schematic representation and mistake the vector (which is always exaggerated as to angle, to make the angle easier to see) that represents the net effect of the sum of actual forces for some sort of actual changed wind angle. Then they produce the verbiage to explain their misreading of the graphic….I think
 
Last edited:
You must log in or register to reply here.
Back
Top