Proverbial BC's and Magical Bullets

[Old-Win]

While watching the Whittington thread grow, I thought I would start new a thread on BC, bullet noses etc.
Now, this is all conjecture on my part but after 15 years of shooting LR, I have tried to sort some of this out. It could probably be shown with Doppler radar but I don’t think many of us have access to one but close to 25 years ago Mike Venturino along with Oehler of chronograph fame did and their conclusion back then was that BC didn’t change much from one bullet shape to another. But today, we read all the stuff about bullets with the same BC’s but different calbers , BC’s and twist rates, BC’s and nose shape, etc.
Ex. 1- Shooting at the Forsyth range during Quigley week is a lot of fun and it allows a guy to experiment with different rifles and different loads. The winds are fairly honest but tricky with the topography and generally will blow out of the same direction for a while. Three of us were shooting the targets from closest first to farthest last so we could get some good practice on the 805 buff later in the day. I was shooting a 40-70SS with a PJ Creedmoor, another, a 45-70 and a 535gr early Money nose and the 3rd, a 40-70SS PP with a Gunn nose that was popular then. Up until 600yds, our windages were almost exact give or take a minute either way. But, when we got to the 805yd buffalo, I needed about about 4-5 min. more windage to stay on target. We like to wait for a fresh paint job so we can see bullet strikes as the buffalo is 8 mins wide. So, without giving any more info on loads, let’s move on.

[Old-Win]

Ex. 2 – I have not observed the greatly reported efficiencies of certain nose shapes of one over the other. I have two bullets that I shoot in my 45-90 with a 17” twist Krieger barrel, at LR. One is a PJ that was made by copying the Sharps PP nose. The other, a BACo money bullet.
While looking at my notes, the difference in elevation at most, is 7 min with the BACo using less elevation. But that bullet is also 20grs lighter and about 40 fps faster.

[Old-Win]

Ex. – 3 We’ve all had this or seen this happen before. Great score at 800 yds, so-so at 900 yds and lucky to keep it on the paper at 1000 yds.

So what is really going on with these 3 examples? Was it nose shape that affected my BC in Ex. 1? Money vs. Creedmoor?
In example 2, why don’t I see greater differences that some are reporting with the slipperier Money nose.
Ex. 3 – Why does the bullet go to pot in the last 100 to 200 yds??

I don’t think it is nose shape at all but stability or instability caused by various reasons in all 3 cases which affects the BC. My 40-70 bullet was too long in Ex. 1. In ex. 2 - Both bullets were stable in the 17 twist Krieger, so there wasn’t much difference in elevation of the two which can easily be explained by velocity difference or changes from one day to the next. In Ex. 3, it’s pretty clear that instability is causing the shooter, problems.

Today’s commonly used nose shapes are elliptical and money. They do fly better but probably for different reasons than we think. I believe it is that these shapes are better at keeping the bullet stable to the long yardages because of weight distribution. (SG vs CP which is beyond me) Remember, BC’s change as our bullet’s speed drops. My shooting partner plotted the elevations for the Sharps PP bullet that I found in an old catalog and the program indicated a BC of .435 at a velocity of 1335 fps. Not close to .50 that some report with their new bullet yet the Sharps bullet was and is a kick butt bullet. Also, remember that Metford designed the original money bullet some 140 years ago and was already in use back then.

So what do you thinks?

[Lead pot]

Man Bob that is a lot to think about and work out.
All through the two weeks between Baker and the Q I worked with two rifles, the .44-90 bn and the .45-90. Both used the same ogive shaped elliptical bullets. Both rifles had the same 1/16 ROT barrels but the bullets where different weight and lengths. the .44 bullet was .432 diameter, 1.460" long and weight 503 gr.
The .45 bullet was .444 diameter, 1.505" long and weight 533 gr.
One would think that the .45 bullet would hold the wind better, but not so in this case under the same conditions. The .44 had less then 4.5 Minutes less wind.

Kurt

[kokomokid]

Old Win How long is your PJ bullet and is it still accurate at 1000? Also is the Krieger a wide land barrel?

[Old-Win]

Kurt, that could show exactly what I'm bringing up! Could the 1.505" bullet be too long and start wagging it's nose or tail at the longer distances?
Kokomo, I believe you're asking about the .45 cal. PJ Sharps nosed bullet and not the .40 cal. PJ Creedmoor. If so, it is stable to 1000 yds. The holes in the paper look good. The lands in the Krieger barrel are wider than my Badger or Green Mtn. barrels. I shot the .40 at LR sveral times and the bullets showed a little tipping for whatever reason. Bob

[Lead pot]

Bob.


Maybe someday at Lodi when one of your team cant make it I could fill in and it would give you a chance to look at the holes I put through the paper.


But the interesting thing is that on average I do better at the 1000 then I do at the 8 or 900 yard line. I send a few rounds down line during the sighter shots because it's the only time I get to shoot past 200 yards at paper to see how the bullet prints.
I also have a Prolate bullet I call the Danielson prolate and it weighs 513 gr and it is shorter then the Elliptical I mentioned above at 1.460" and it gave me a problem at the Montana 1000 during the practice day, it just would not stay on the 4' stop sign at the 1000 line. I shot circles around it all day. I would shoot 10 rounds using it and maybe two would hit, not a vertical problem but a 360 degree misses. The longer elliptical hit 13 straight and you can call the hits a tight group from the stick pins Carol had on the paper. During the match I had full wind in the MVA Buff Soule sight and I shot 4 on #3 and 11 counting the fouling sighter shot we where allowed to shoot on #4 both the stop signs. Is it the ogive shape or the .045" longer bullet shot with the same load for the match that shot better????


These things I have a hard time coming to conclusions WHY??? It could be that the 1/16 ROT stabilizes the 1.505" bullet better then the 1.460"

[Don McDowell]

When looking for a good long-range bullet for the 44-77, I found out the hard way, to test those long bullets on windy days. If they are marginally stable on calm days, there's a pretty good chance that they'll go wild on windy days.
Testing on steel is good if you can go check the steel for exact impacts, and repaint after 5-10 rounds, but other than that it's just a wag where the bullets are impacting and if they're point on or leaving a sideview profile..

[country gent]

The new labradar can help here figuring accuraate BCs and showing velocity drops. Mine will pick up the long 45 cal, 40 cal, and 38 calibers at BP velocites out to 175 yds. ( I havent tried it farther yet.It reads each shot at 5 places from muzzle (vo) to each step set into it by you when setting it up. With these numbers you can see velocity drop diffrences with diffrent style bullets. Or there are programs available on line to use these numbers to figure actual BCs. The numbers given show the diffrences in velocity drop effectively allowing an idea of which bullet carries better. As far as stabil;ity that has to be determined thru shooting and known rifle twist / bullet length. Seeing the velocity drops over range is interesting to say the least and can be an eye opener when selecting bullets

[Old-Win]

What would be nice is if that Labradar could be used at the longer distances to show when there is a large drop off in BC's. Like when a bullet nose might start to oscillate. Bob

[BrentD]

Bob,
I think nose shape is related to stability in a big way. Blunt noses have more nose drag and a greater tendency for the bullets to want to let their bases try to pass their noses. This will give you the instability, esp in the last couple hundred yards.

FWIW, I have two moulds with identical noses. One is 1.46" long (513 grs) the other is 1.51" long (537 gr). I have shot both out to 1000 yds, and done so with both 16 and 18 twist .45 barrels. I have won with both the long and the short bullet in the 18 twist, but it was obvious to me that the longer bullet was much less accurate and more wind-sensitive at 1000 yds than it is in the 16 twist rifle. I only shot it in the 18 twist because I was forced to when the 16 twist broke down in mid match (happened twice). The shorter bullet in the 18 twist seems to be the equal of the longer bullet in the 18 twist. I have shot many other blunter nosed bullets out to 1000 yds and they did relatively poorly to be honest. Even though their weights and lengths were comparable, their precision was not even close.

I measure my own BC's They are usually around 0.5 for the first 100 yds.

DanT reported BCs in the 0.6 range and even higher (much higher), but I've never been able to measure a bullet with that sort of BC and I am suspect that won't hold up.

[country gent]

I wonder if a second lab radar down range at 200 yds set to doppler trigger would pick up and give further readings ( possibly out to close to 400 yds) when the bullet passed by it? Im getting bullets picked up out to 175 yds now with mine But I only have a 200 yds range to test on. Wether it would pick up these bullets farther out I dont know. But muzzle to 175 yds should give an pretty close BC. I can remeber setting up 2 chronograpghs one for muzzzle and second at 200 yds to do this. WIth the Nasa's and such I normally get around a .5 BC. One thing is to test at the longest distance possible when possible.

[17nut]

The slower the bullet go the less BC has to say.

It is right around Mach 1 the beast rears it's ugly head.

Look at this and ponder:
http://i295.photobucket.com/albums/mm153/Chickenthief/Skydning/lapuadrags_zps9ab1643a.gif (http://s295.photobucket.com/user/Chickenthief/media/Skydning/lapuadrags_zps9ab1643a.gif.html)
This curve is from a non applicable Lapua bullet but the theory is sound.
Most all long range rigs shoots faster than 1100+fps thus the bullets have to pass down through the ugly zone and that is when BC really matters.

[BRUCE MOULDS]

17nut,
your graph shows the transonic zone perfectly, or as you call it, the ugly zone.
this zone is generally considered to be from mach 1.2 to mach 0.8.
many higher b.c. bullets will not remain stable here, the most infamous being the 168 gn sierra matchking in 30 cal.
certain nose shapes exhibit lower drag, and have greater stability in this area, and these include the elliptical and the money/metford shape.
most smokeless rounds go transonic around 1000 yds, give or take, whereas our bp bullets are in this zone at the muzzle, and stay there out to 500, 600, or possibly 700 yds depending on their slipperiness.
we have to retain accuracy there , and once out the other side our bullets seem to get more slippery, but in fact it is just that there becomes much less nose pressure on the bullet at those lower speeds.
long range bullets need high b.c., and once you have played with nose shape, the only way to achieve this is to lengthen the bullet.
the longer the bullet, the greater is the distance between the centre of pressure and the centre of mass, causing the bullet to want to overturn more.
centre of pressure is at its most forward point in the transonic zone, but the centre of mass remains the same, making the overturning moment at its greatest in this area.
sufficient spin must be imparted to the bullet to overcome this.
shooting against 308 palma rifles from 300 to 1000 yds has demonstrated that b.p. bullets have about 3x wind deflection out to about 600 to 700 yds, when the difference reduces to 2x.
they are still supersonic, but I am transonic and then become subsonic.
there is nothing magic about any bullet, just some nose shapes that demonstrate less drag and more stability in the transonic zone.
spitzer bullets are not included in this group, being more suited to supersonic flight.
sometimes a bullet will have a little wobble and become stable again. increasing the twist or shortening the bullet will often solve this.
when in full wobble it becomes a little side-on, thus having a bigger frontal area, and hence more drag.
such shots will shoot low and also have more wind deflection.
a most interesting subject.
keep safe,
bruce.

[Old-Win]

Country Gent, Could you give us some examples of what some of the velocity drop offs are that you've found using your Labradar? Can you include the bullet shapes?
Kurt, I talked to a shooter at this weekend's gong match and he said you did well at the Forsyth 1000. Did you use the same bullet all the way through the match? I'm curious as you said that the longer 1.505" didn't shoot as well as your shorter bullet in the 16" twists yet it should have. I played on a 22" steel gong at 600 yds this weekend and shot about a 1 moa group with an elliptical Sharps bullet (really good for me) and another style bullet didn't shoot well at all. The one that didn't shoot well had much deeper lube grooves and a Creedmoor nose yet both were about identical in wt and length.
Bruce, I'm envious of all the shooting you get to do at the longer ranges. (vbg)

[Lead pot]

Bob.

No I shot the first two targets with the shorter bullet. The one on the left what I call the Danielson on the square larger targets,(I think they are larger targets.) and I just could not hold them the way I felt they should. Yes the wind was tough but I felt they should have held better then they did. That bullet as well as the longer one on the right, when working up a load before the Quigley shoot shot sub MOA @ 200 yards several times before I loaded the 1400 rounds for the .45-90. I shot the prolate at the Quigley and placed 15th at the end and it held very good in that strong wind with all the windage my MVA Buff Soule had on the 805 Buff.
When I went to shoot the Mt. 1000 I struggled with that bullet the day before the match at the 1000 yard targets. Tom Mace and Glen Gipson where watching back by their Camper when I was shooting, I must have missed the stop sign 45 out of 50 shots I took at it. It just would not hold. Shot circles around it. I walked over to them and I said, it's not going to work.
The next day I started on the #1 the square and hit 5. 5 on #2 Then I pulled out the last 25 rounds with the longer bullets I had left over from the Q and shot the stop sign with them. The #3 was in the shadows and I had a problem seeing it. Shot the bush several times above the target :) #4 when I shot it it was in good light and my sighter shot hit and the following 10 stayed on it with a very tight group in the white and just outside the with. Carol had all the spotter the spotter pins on top of each other except for three that where well inside the edge that where pushed out by the wind gusts.
Bob the short prolate shoots very good in the 18 ROT rifle but I think in the wind past 800 it does not hold in the 16 ROT. But the rifle is new and I have not had much long range load work with that bullet. http://i22.photobucket.com/albums/b302/940Leadpot/IMG_2812_zps3ek1emps.jpg (http://s22.photobucket.com/user/940Leadpot/media/IMG_2812_zps3ek1emps.jpg.html)