J ECustom wrote >I think you mean BCs go up with weight and shape not SDs (I call SDs the difference from load to load velocities).<
I'm sorry. I should define abbreviations when they have more than one meaning or aren't common usage for everyone. Bullet makers often publish the value of Sectional Density (SD) for their bullets. That SD is simply the mass of the bullet divided by the frontal area. In the United States the units are usually pounds per square inch (PSI). The number increases for heaver or more slender bullets. It says nothing directly about drag or stability. Your use of SD I believe mean Standard Deviation of the muzzle velocity telling how uniform the velocities are shot to shot. There are a few other meanings of SD.
http://www.all-acronyms.com/cat/0/SD
> I hear you, but what I was talking about was after it went subsonic the effects would be less
than if it were a lighter projectile.<
I'm talking about that too. An unstable light bullet may or may not deviate more than an unstable heavy bullet. In both cases it depends on the bullet's stability factor vs time and how much the bullet yaws. Bullets shot at long range are most likely to yaw when they are at transonic velocities. If they do and if they regain stability below the transonic range they will fly at some new deviated angle. The magnitude and direction of that angle is impractical to calculate.
> With a BC of over 1.0 the 50 BM bullets have all of the ballistics and then some of a bullet that has a BC of .7 to .8. and weigh 300 to 400 grains<
A bullet with a Ballistic Coefficient (BC) over 1.0 may not even have "all the ballistics" of a another bullet with a BC over 1.0. How could it have "all of the ballistics" of a different bullet if it doesn't travel the same trajectory? It will fly further than a bullet with a BC of .7 to .8 (fired at the same velocity) but only if both bullets remain stable. It's possible for the .7 to .8 BC bullet to be less stable than the bullet with the BC of 1.0/ BC numbers assume bullets are stable but it in no way guarantee that they will be stable at any particular place in the trajectory. Bullets can (and do) sometimes change from stable to unstabe and back again. Stable and unstable is not an on and off thing. Any spin stabilized projectile has both a static and dynamic stability factor which changes constantly along its trajectory. It's not even a certainty what stability factors are optimum. A value of 1.5 stability is often stated as a good chooice, but a smaller number may improve group sizes a bit. Even an unstable bullet may fly with little deviation but there are no spin stabilzed bullets which can fly in the presence of gravity with no yaw or precession, though the effects can be tiny as regularly demonstrated in short range benchhrest matces. Most ballistics programs don't even attempt to calculate stabilty effects and ignore it completely. Those that do attempt to calculate those effects (usually called six degree of freedom (6DOF) programs can only give a rough estimate the magnitude of deviation of the flight path. That's not because th computations aren't correct but because the models are never perfect and small variations in the input conditions cause large changes in the results. Stability factors are real and do affect group sizes but hey are usually less than the effects of wind and velocity dispersion.
This site may explain the results of such computer programs. In the output data the effects of wind and drop are being ignored. These are the secondary effects which most ballistics programs don't even calculate. The graphics on the site exaggerate the magnitude of the stability effects but they are real in normal spin stabilized projectiles.
http://www.nennstiel-ruprecht.de/bullfly/index.htm#Top_of_page I've several times seen the helical trajectories in 50 BMG vapor trails when conditions produce clear trails. Its usually worse (larger magnitude) for heavier and longer bullets and most easily seen when bullets are spun much faster than what's necessary to stabilize them. The diameter of the helix can be less than an inch and still be easily visible for a spotter looking over the rifle barrel parallel to a part of the downrange trajectory.
> If you could get a 800 grain .510 diameter bullet to a velocity of (3400+ ft/sec) then I feel that
you would have the new contender for the best long range weapon or if you loaded a
down to a velocity that placed it at the same transition velocity as the 50 BMG i have no doubt
which one would end up on top<
You can get into the 3400 feet per second (FPS) region with a 50 caliber bullet and rifles exist which do that. Do a web search on the 50 Uniroyal cartridge. it's a 20x102 millimeter (mm) cannon case necked down to .510" and shoots standard 50 Browning Machine Gun (BMG) or target bullets. It's got 560 grains case capacity compared to 300 for the 50 BMG. Barrel life is not good. The United States Air Force (USAF) experimented with similar cartridges in the 1960s for use in supersonic aircraft but heat seeking missiles won out.
>But it would be mean to shoulder fire unless you had a very heavy rifle with a very effective
break.<
Short barrel life was the main problem. High velocity by itself doesn't add much range. Interestingly the 50 Uniroyal and the shorter 50 BigMac are not considered destructive devices. Even a semi-auto version would be classified the same as a Ruger 10/22 by the BATF though illegal in a few states. The 50 Big Mac was built by McBros as a target rifle but wasn't very competitive.
> Having shot quit a few big bore black powder cartrige rifle that went subsonic at less that
200 yards but could still be accurate at 900 to 1000 yards because of large (500grain+ Bullets)
with very poor BCs usually less than .300. mass does matter. shape helps to achieve better
BCs that produce better accuracy at long range along with higher velocities>
I presume you're aware that a transonic cast lead rilfe like you describe has considerably greater wind deflection and vertical stringing from velocity variation than a 50 BMG. Check the aggregate group sizes from 1000 yard black powder matches compared to Fifty Caliber Shooters Association (FCSA) 50 BMG matches. National Bench Rest Shooters \Association (tNBRSA) 1000 yards benchrest matches with smaller centerfire cartridges have even smaller group aggregates. Higher velocity helps more than anything at only 1000 yards.
> I may be wrong but until someone can prove it I will keep an open mind and If a 40mm
has more range than a 20mm and a 20mm has better range and accuracy at longer ranges
than a 50 BMG then I have to assume that a 50 BMG with the same velocity as the 338 would have an edge<
Sure, big guns can shoot further with excellent accuracy. We're back to the 120 MM Depleted Uranium (DU) penetrator of the Abrams tank. Low wind deflection, low vertical dispersion, and never goes transonic at useful ranges. Just the thing for deer hunting at over 2000 yards. The gun is heavy but it comes with it's own off road vehicle. Some minor problems with it are cost, availability, Bureau of Alcohol Tobacco, and Firearms (BATF) approval, hunting laws, and radioactive venison.
I'm not trying to tell you that a 50 BMG can't go transonic and still be stable with heavy bullets or not. In my first post I suggested you try it and find out. I'm certain that an 800 grain Barnes solid will be less stable than an M2 ball round when it goes transonic. In no way does that mean that the 800 grain Barnes solid won't have adequate stability. I expect that the M2 ball would be over stabilized for reasonable air density but I really don't know. I've never seen data on the rate of spin loss for either bullet at long range (or any range). You'll probably need to do your own shooting tests. It wouldn't be useful to you if I did the tests because where I shoot is at over a mile elevation and I'm reasonably certain both bullets would be stable from my rifle. You haven't mentioned in what atmospheric conditions, particularly air density, you might want to shoot them beyond their transonic range, and I don't know the twist rate or velocity of your rifle.
You could set up a big target (maybe 8 feet square) at around 3000 yards, which would be well subsonic, and you should be able to get on target reasonably easily with the help of a spotter. If you can get groups under 3 feet the bullets are no doubt well stabilized. If larger you'd need to decide if the group size is expanded by wind or velocity dispersion (the SD you were talking about). Most FCSA 1000 yard matches are won with approximately 10" aggregate groups. 3 foot groups at 3000 yards would require good conditions, good ammo, and decent marksmanship (sub minute of arc (MOA) ) but it seems practical with little equipment, just a place to shoot and a target. Wind flags and a chronograph would help sort out the effects of stability from wind deflection and velocity dispersion.
> Anyway it is just a debate and still open. <
It's a interesting discussion but until you (or others) fire a few shots you're not likely to to know the answer to the question you posed. I'm not saying the answer will be that the heavy bullets will be stable or not. . I'm just suggesting why extrapolating from shorter range nformation won't give a meaningful answer. Maybe someone has already published information on the accuracy of various heavy 50 BMG target bullets beyond their transonic range but I doubt it. I don't remember any such tests in the FCSA publication "Very High Power". That would be the most likely place to find the information. Perhaps such tests have been done a the Ballistic Research Laboratories (BRL) at Aberdeen Maryland, but I've not found publications with web searches.
