First, the BC of the 300 gr. Sierra bullet changes every single meter downrange, refer to the image of the different shots of the 773 gr. LRBT above. That curve represents thousands of BC values. Using a single, or even 3 BC values won't yield accurate results. The varying BC values in the data curve above are every 100 meters yes, but they are averages of BCs taken every single centimeter from 10 meters to about 5000 meters, more or less, depending on the shot, downrange. You guys are on the button with yaw and pitch characteristics. The "controlled spin" patent that LRBT has on it's bullets addresses this issue. Now many say it can't be done, but the YPG and APG ballistics guys disagree and said that it was effectively DONE.
I've attached a plot image from the YPG test. That fine (not so fine on this upload) line represents the stability of the controlled spin bullet during supersonic through transition and into subsonic flight. No bumps and dents in the line. As the bullet starts to yaw, the BC value begins to drop, sometimes the straighten themselves out, and the BC value climbs again, after transition, they always climb, some are higher in the subsonic range (BC) than they are supersonic.
Brains smoked, here's the plot. Last PS, the data string from 1 shot, printed in 10 cpi is 198 pages long. A different BC shows up 3-4 times per page, depending on how you buffer the data.
Thanks Dean, but that doesn't really answer the question. If the above bullet was fired at 900 m/s, would the 780 m/s and on portion of the velocity vs time curve be vastly different than the one above or would it just be shifted over a little bit? If the latter, then the speed of sound would not be reached as quickly, correct?
Trigger, i'm sure i can answer that for Dave, it's because the bullets don't shoot worth a hoot! i know, i know, they shoot great. i'm sure every once in a while it seems someone will have a rifle that shoots em pretty well. but it's rare. just ask the fellow in Ohio that has been trying to get them to shoot for 3 years. he's got great equipement, a full tricked out heavy gun built by a good smith. did i mention he's gone through 20 barrels in this time and has never, ever, even once kept all the bullets on paper much less done well in a match. i think Dave's point was it doesn't matter if a bullet has a BC of 2.500, if you can't hit what you're aiming at.
I agree with you Kirby, this an interesting conversation. I am learning something new everyday. I never looked at ballistics in this fasion. I am trying to make sense of the whole thing. Anyhow, I hope the conversation continues. I am glad I posted this topic.
Kirby, I e-mailed you back regarding your recommedations for my 338 Allen Mag project, just wanted to let you know. I hope to hear from you soon.
My point with the Lost River Bullets are experience in the 408 cal bullets, these are the patented controlled spin, yes i have tried them in three different rifles. They shoot just ok, not anywhere close to match quality. The quality control is not good for a bullet that is priced as is. You never see a Lost River bullet win any long range match, why is that? Even with the special barrels made exclusivly for the LRB bullets, they still are only just ok. Now there is another bullet company making a similar 408 bullet, that will out perform the LRB in accuracy. My customers no longer use the LRB bullet, they prefer the other manufacturer's bullet. This is why i said, IF and When Sierra has something to offer, then you will have one awesome rifle, but then you will be back to the 300gr MK delema, lower BC bullet, but more accurate. All these curves and tangents don't mean a whole lot to the guy hunting big game in the 1000-1200yds, he just wants to know where to aim and see the bullet hit what he is shooting at. I know its a military sorta thing and they would be more interested, that is the whole thing behind Chey-Tac anyway, they want gov contracts. I told Warren Jensen the 408 will die without other bullet manufacturers in the mix, he then threatened to sue me for patent infringements. Chey-Tac and Lost River at that time wanted the Monopoly on the whole thing. I refuse to buy another LRB bullet.
Sorry guys, while i'm not a cheytac fan, the 408 DOES shoot. I've shot them all from gun #1 to now, dozens of them, built some of them. I shoot 338 250s and 270s, and have seen them shoot by navy shooters, army, and many other units. You ARE outnumbered on that. The internet "push" against these bullets is misguided i think. Dave, i believe you build a good gun, i also believe you are using barrels that are not compatible with these bullets. Lawton in Mt, builds them right. Just had an AI gun here shooting 270 gr. LRBT 338 bullets, and HE is convinced.
I know, I know, it' takes a special barrel, but isn't a specific twist a special barrel? Doesn't the M24 have a 1:11.25" twist for JUST the old 173 gr. M118 SB round? PLEASE come to an extreme range shoot in Idaho and LOOSE to these rounds. Just had a 4 day shoot here and all those guys were convinced. The only guns to hit the 2600 yard targets were shooting LRBT solids, a 375 rifle, a 408 rifle and a 338 lapua, shooting 270s. Results on are my website. Dave, what bullet are you shooting in your .408 guns? Please don't tell me that brass junk.
Also, on these other guys that can't make them shoot. Can you hook me up with them? I'd like to know their gun setups. Tight bores that have to squeeze bullets to make them shoot won't do the solids, the FCSA shooters knew this years ago, they simply adapted.
I publish results with my guns and groups. Witnessed, this target was shot by the owner, with 3 witnesses. I built the rifle, 375 SOE gun.