Home Forums Hunting & Shooting Long Range Hunting 30 Cal BC Test

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DD,
"I ain't JonA but that fella Pejsa makes my head hurt. "
Ya I know.But his discription of what his math can do to the slop of the curve.Fits what JonA is looking for.I think.
From what I can read comming up with a curve based on drag for the bullet your usuing is much more accurate than say Sierras multiple BCs.
His math goes over my had real quick.
dave

Jon,

There is a very interesting article in this month's Precision Shooting about VLD vs non VLD bullets. The author's take is the way the a bullet engages the rifle is critical and can make a big difference in how true the bullet flies. He points out that once a bullet is deformed in the initial firing process, it stays that way. VLDs seem to be especially fussy about how the contact the rifling. The answer to making VLDs fly like they are supposed to is to cut the leade specifically for the VLDs. The article in next month's PS is going to explain more.

dave, you may be on to something there...will take a second look. Pejsa's math doesn't bother me so much as his prose....it seems like he's yelling or something...and we're on the Group W bench a jumpin' up and down yellin'.... <img src="/ubbthreads/images/graemlins/crazy.gif" alt="" />

Dave,

The only catch is Sierra multiple BCs seem to be spot on. I can chrono a Sierra bullet, plug the numbers in Infinity, crank up the scope the requisite clicks as per the program, then hit within a foot vertically at 1000 yds with the first shot. Then again, maybe it IS all just chance............... <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />

Thanks for the heads up on the VLD article, Blaine. Sounds interesting, I'll check it out.

On the Sierra BC front, within a foot at 1000 just doesn't tell me much. For example, from my rifle at my Montana altitude, the difference between Sierra's published BCs in stepped form for the 210 and using a constant .647 as I measured (which is a pretty big difference) only makes about 3" difference in trajectory at 1000 yds. With a relatively accurate starting point with a high BC bullet from a decently sized round, things aren't going to get really interesting trajectory-wise until beyond 1000. Running the comparison at 2800 MV it's about 10" difference. Starting to become significant, but still within a foot for such a huge BC/drag curve difference.

I'm working on getting locations worked out for 1300, 1500 and 1 mile targets. That's going to be interesting. Curve differences that are so small they get lost in the noise of other variables at 1000 will become quite apparent.

Thanks for bringing that up, Dave. I had seen that before, I even found I had a spreadsheet on my computer using Pejsa's method. I must have gotten distracted before I could dive into it and forgot about it. <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />

I was wanting to have a better handle on the math before I commented, but I've been busy (testing even higher BC bullets! <img src="/ubbthreads/images/graemlins/laugh.gif" alt="" /> ) but I'll give you my thoughts on second glance:

I think it has the potential to provide very accurate data, in many cases more accurate than using standard drag curves. Just using the software and/or the math without good data collection I don't see much of an advantage though. Where I see the possible advantage is if you have a 3rd piece of data from far downrange. Say I repeated my above but put the second chronograph at 1000 yds or so. Or I get really accurate drop data at 1500.

I could just adjust the BC to reflect the average over that distance for whatever standard curve I thought my bullet would fly close to. This would put me exactly on at that distance, under those conditions. But depending upon how differently shaped the bullet's actual curve is from the one I'm using for the calculations, it could be off significantly in the midrange and way, way off at distances much farther than the distance at which I collected the last piece of data. The bullet might fly really close to one of the standard curves, it might not. Or I might guess the wrong curve.

You're basically taking two differently shaped curves and matching them up at two points, ensuring they'll be off everywhere in between. How much depends upon how different they are. So with a data point at 1000 yds, I'd be dead on at 1000 but I could be way off at 1500. At 2000 yds I could be missing the target by several feet, even with all the other variables taken care of accurately.

For this, I think Pejsa's method could be much more accurate. Instead of moving a fixed curve to match your actual curve at two points, adjusting the constant adjusts the shape of the curve, letting you simulate the drag curve of your particular bullet. If done properly, I think it has the potential to be much more accurate at ranges farther than your last data point vs. assuming your bullet flies to a standard curve.

I have played with the math a little over the last couple of days. For most BC/velocity combinations you can think of, you can change the constant to fly to the G1 curve within an inch or so out to 2000 yds (or where it goes transonic). A different constant simulates the G7 curve about as accurately (those are the only two I spent time comparing so far). If your bullet falls in between somewhere, I think the Pejsa output that matched your data would likely be more trustworthy at extreme ranges than just picking a curve that might or might not be close. Or say Sierra's data is accurate for the 210--it would be WAY off at 1500 for any curve even if I had it nailed at 1000. Making your own curve would be the only way to even come close.

The above was for really high BC bullets at supersonic ranges. Obviously lower BC bullets fall below that before 2000 and the math in the spreadsheet I was looking at doesn't cover that portion of it. In general, smaller rounds shooting lower BC bullets will have all these different curves show significant trajectory differences at much shorter ranges than my 300. Things won't get too interesting for me until I get well beyond 1000.

One word of warning in general though, like anything else it's only going to be as accurate as your data collection. It's pretty common for people to adjust BC's in software to match actual data via the standard curves and there is nothing wrong with that. But I do feel many people do it way too soon, without eliminating other variables that can cause errors much larger than the differing drag curves will at the ranges most people shoot. Accurately measuring Baro, temp, etc. Using a velocity they got from a cheap chrony last month. Not knowing if their scope clicks are supposed to be 1/4 MOA or 1/4" per 100 yds much less what they really are. Stuff like that can cause errors large enough that all this drag curve talk is just mild noise in the background.

Those are my thoughts, anyway, just at second glance. It ain't no doppler, but it might be pretty good if one goes through the effort of collecting good data to shape it. Maybe a good shot better than most ballistics programs. I'll look at the math more closely in the future and will be putting this stuff to the test at much longer ranges in the future. It'll likely teach me a few things...but it should be fun. <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />

Dan, Metro is 78% humidity, ICAO is 0%. Is that what you meant?

JonA, do not mean to hi jack your thread, but I have a stock in the classifieds that you may be interested in........Blake

No, I recalled ISA contained a standard humidity factor, somewhere in the 40-50% range. Might have confused that with something else though, I'm reaching back in time awhile. Maybe I've entered a parallel universe... <img src="/ubbthreads/images/graemlins/grin.gif" alt="" /> Not important I guess. Thanks for your thoughts on the matter.

Dan

JonA great data! Thanks for sharing! Can you share with us some information on the bullets you plan to be shooting in the near future?

Thanks again,
JonK

Sure.

There won't be anything magic about them--the most difficult thing was just trying to find somebody to make them (Richard Graves of Wildcat Bullets rocks!). They'll be a nice pointy VLD/ULD style shape, just much longer and heavier (higher SD) than 30 cals have been made in the past.

The goal I've had in the back of my mind for ages is a 30 cal bullet that will run with (or even beat) the 338 cal 300 grain SMK ballistically. I won't know for sure until I shoot them over the Oehler lie detectors, but they should have no problem accomplishing that. They'll make all the bullets in my above test look pretty silly BC-wise, that's for sure.

So far I've just played with some initial prototypes to sort of test how long and heavy a bullet my rifle can handle. These have been over 1.80" long and weigh 290 grains. <img src="/ubbthreads/images/graemlins/laugh.gif" alt="" /> My 300 RUM thumps them out there nicely at 2680 fps over a mild load of US869. The final versions will be lighter, probably around 260-270 grains and will go somewhere in the 2800-2900 fps range--longer barreled rifles will likely push 3000.

While super high BC was the primary reason for wanting such a thing, better terminal performance was a close second. These are built on a tapered jacket, bonded core optional--very much a "hunting bullet." If you've tested the 240 SMK, you probably have some idea of the potential such a bullet will have. That'll be fun to test as well.

Of course I know there will be those who point out nobody should "need" such a bullet and that I must be nuts.... But it's sure going to be a lot of fun. That is why I do this stuff, afterall. <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />

JonA, I am very interested in your resultwith these heavy for caliber Wildccat bullets. After read you sucess with US=869 and the 240SMK. I ordered a 30 Cal. ABS Carbon weapped bareel with a 1 in 9.2 twist to finish at 30" and am planning on building a 300 RUM bulit especialy to shoot the very heavy for caliber high BC bullets.
Thanks, for the insperation.............. <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />

John, I had a brief email flurry with Wildcat Bullets a short time back, inquiring as to BCs...found it interesting that he would not dicuss BC beyond stating that he didn't care to enter into the fray...would be interested in what you find on that horizon.

DD,
If you looked at some older posts on the LRH forum you would see that there were some heated discussions concerning BC.
That, I believe is main reason why he doesn't want to get into it. If you are interested in the 7mm 200 ULD/RBBT I would be glad to tell you what BC I am using for my BP/Alt/MV on Exbal. I am not making any claims of true BC, but what matches up with my drops.

Ernie, would appreciate that info if you don't mind...here or PM, whatever. Would be willin' to bet that a gross majority of folks discussin' BC don't really know that much about it, a case of knowledge being inverse to testosterone. I'd be tryin' the Wildcat .257s if I was twisted enough...mebbe later for that bore.

Wow, jwp, that should be one fine setup!

Dan, like XP said, Richard got yelled at a while back for providing computer-based estimates. Not because anybody actually tested and found them to be off, but because some people like to yell. So he decided to just stop and let people find out for themselves. My expectations aren't based upon anything he or anybody else has said, but my own experience and understanding of the physics behind it all.

DD,
Right now I am using a multi BC for the 7mm 200 WC, like Sierra does. I use Exbal on my home computer and on a pocket PC.
BC is listed as .825 @ 2700 fps, .8 @ 2300 fps, and .75 @ 0 fps.
My MV is 2706 with the 200 grain ULD RBBT Wildcat bullet. My MV is from 300+ fps slower than many guys using this, since I am shooting this bullet in a 7MM Dakota specialty pistol/Remington XP-100 (Center-grip). Guys using rifles with substantially higher MV's are using higher BC's to match their actual drops.
I have not shot this pistol past 1000 yards to date, but have shot it @ 600 yards on steel and paper the past four weeks.
When I was shooting @ 1k this past May my drops were matching the BC I listed above. It is really nice in the wind, and gives a field shooter (no access to flags) some fudge room @ 600 yards. All of my shooting has been off of a bi-pod and my 3-shot groups hover in the 3"-4" (some a little better some a litlte worse). I know that isn't anything special, but since I have been shooting without a spotter, I have been focusing on wind (watching the Kestrel) since my shooting locally has had some crazy wind lately South Central Kansas, and I have rushed some of my shots and have ended up with more vertical (3-4 inches) than I typically do @ 6. I am going to make sure my bi-pod/bag tension is consistent this week and set-up my Kestrel so I can see it without having to hold it.

Thanks for that, impressive performance indeed.

Jon, I just saw this data. Great info. Thanks for doing the test and sharing the results. I wonder if you have tested any of the Wildcat Bullets made by Richard Graves up in Alberta, Canada? Thanks, Rufous.

I haven't tested any for BC yet. I shot some 290 flat bases only shooting them out to 700 yds and they did well (and boy to they whack that gong hard!). But the 290 RBBT has proven too long for my 1:9 twist. There are several people getting 1:8.x twists as we speak for it...it's a beauty:



From left to right: 200 AB, 210 SMK, 240 SMK, 290 Wildcat RBBT ULD, 300 SMK (338 cal).

I should be testing some shorter 265's that should work in my 1:9 pretty soon. I'll likely be using a bonded version of that for elk next year.

I figured I should update this when I noticed Sierra has changed their ratings for the 210 SMK. They now rate it as:

.645 @ 1800 fps and above (Which means from the muzzle to about 1200 yds for me)

.630 between 1600 and 1800 fps
.600 between 1400 and 1600 fps
.530 @ 1400 fps and below

Compare their old rating (that made for the whacky curve above):

.620 @2500 fps and above
.575 between 2500 and 2200 fps
.490 between 2200 and 1950 fps
.425 between 1950 and 1700 fps
.375 @ 1700 fps and below

As you can see, this is a big improvement and if plotted on the graph above would come much closer to real drag curves (specifically the G5 and G7) than the whacky data they had before did.

So, they ended up a whopping .002 off from my data. And I don't even get paid for this stuff! But it's nice to see the change. I haven't yet tested myself, but have seen enough testimonials of this bullet (as well as the Berger 210 with very similar shape, etc) well beyond 1000 yds that show them doing very, very well.

However, I suspect the 208 A-Max is going to beat it by enough to make me lose interest in it. Maybe it's time for another drag race!