Home Forums Hunting & Shooting BPCR Postell Bullets?

Brian, it's not just less windage and elevation - but rather how much less. The mega-dramatic claims being made here, don't need particularly sophisticated experiments to be shown to be false. Such ridiculous claims require monsterous differences in aerodynamics that are simply not possible.

From Dan's essay above, he gives shank drag a contribution of 2-3%. There is no way you can make a 2-3% change (the maximum one has to play with in comparing PPBs to GGBs), produced windage differences of 3 fold. Can't happen because 3% is two orders of magnitude less than 300%.

These claims don't even get to the sniff-test stage, much less past it.

PPBs benefits are going to be - AT MOST - in the range of 10%, and more likely less than 5%.

I do my own testing of BCs so they are empirical, not theoretical measures. They are not magic, nor even single constants. But as we all know, they are quite useful, particularly as comparative measures. They also seem to be quite appropriate for these types of cartridges and velocities. I have used them with the JBM website spreadsheets noted above, to produce estimated sight settings at 1000 yds using only a measured muzzle velocity, and BC and a 200 yd sight setting. The software came within 2 points (0.02") of being right on the money.

Brent

Bore bump up does not affect BC if BCs are measured at the range rather than simply estimated from initial bullet shape, prior to firing. And that is why I point out these are empirical BCs, not some estimate from a drawing of a bullet profile.

This is not rocket science.

Brian, I'm really not trying to do anything other than post some facts relative to the discussion. Exterior Ballistics IS a very complex subject. Not my fault. Comments made since my last post all have merit, as do your own. The end results are what counts.

I'm mostly in the "close is good" side of the discussion. Minute variations are just that, but when taken in sum measure they can add up. Long range tends to illustrate these variation profoundly, but in context of shorter distance I don't think they amount to much. Defining "long range" is a slippery slope in its own right and I won't bother with that. When the range gets long enough that performance doesn't match needs, it's time to find a solution.

I do think that PP bullets have benefit over GG in several regards, but also think those advantages are less obvious and profound than most assume. In a no wind situation with all other variables as closely regulated at practical, I don't think there is an intrinsic advantage to either style as measured by precision. Add some wind to the equation and I give small advantage to paper patch. I think shooter skill in doping wind is far more important.

Dan,.....REALLY enjoyed your 'Complicated' post.

Well done, Se�or !

GTC

Ranch, what you say is true, but I think the question is how much difference it makes. We're talking a small difference of diameter. In using your numbers. Compression of the patch during obturation will make it less, so for sake of discussion, call it a .008" diameter difference at muzzle exit. Given a base reference of a .458" groove, full obturation and a 500 grain bullet, we are talking a difference in sectional density of .340 (GG) and .352 (PP). For a given form and diameter, BC is proportional to SD. I see some small gain in the BC for the PP bullet, but it is not profound. A somewhat crude BC calculator I use on occasion puts the respective BC's at .340 and .353. As indicated earlier, I note the comparison but don't put a lot of stock in what it means. Actual shooting, recording and measuring is the way to do that.

Where it gets a little more murky perhaps is how this influences long range changes in POI. Certainly to some degree, but I'd not try to quantify that without more info on the table.

I don't recall the forum where I saw this, but just recently I read something by KW regarding difference in POI between two bullets essentially the same save for form. Both were paper patch if I understood correctly, so the variables were much reduced. I also believe the range where these differences were observed to be one mile. I recall the measure as over 120". May have the numbers screwed up, but don't think I'm far off. Anyway, the point is that small differences can have large effect at long range. I think the definition of 'small' and 'large' is application driven here and not an absolute measure. Put another way, "elk small" and "prairie dog small" are two different things.

That's mostly the message I have on this, but since I specialize on slaughtering hogs at ~10 yards with wee .22 CB Short RF bullets, I don't care if the Devil hisself says it can't be done, he's wrong.

Furthermore, if one believes they can or can't, they're probably right in both instances. Last year out in Cody I had occasion to take my first shot with a new rifle at 200 yards using the bullet style above in the pic. KW was watching the German Ring target thru a spotting scope at the adjacent bench. First round went thru the x-ring, this in a crosswind of about 15 mph. I swear to two things about that: 1) I shoulda stopped right then and there. 2) I'd give a framed Franklin to have had a picture of KW when he turned to look at me after the shot. It was sort of a perfect blend of "poker" and "caution" cut with a little "speculation". I'd hang it on the wall if I had it, I swear I would.

Hows about a round of beer?

Even a blind hog........

Thanks

Dan it would have to be one of the great priviledges in life to sit and have a beer with you, anywhere anytime...

+1!

Ed

curious...thinking about these bullets versus rifle bullets intended for supersonic use, like say a Matchking or VLD's.

Do these BPCR bullets have rounded noses to reduce drag, once the bullet drops into subsonic ranges? Or is there some other reason why the noses are not sharp pointed?

For the most part the long skinny noses in the highpower stuff, don't do much for the bullet at bp velocity. The area where these bpcr bullets operate it's more important I believe to have a balanced bullet that won't loose it's stability when going back and forth thru the sound barrier.

Tex, there's a lot of conflict with that idea for lead bullets. On one hand VLD designs are long for weight and this requires faster twist rates. While harder alloy bullets can deal with that, there is a relationship between alloy hardness and the pressure required to obturate the bullet.

Bullet's BHN x 1422 = pressure in pounds per square inch required for obturation.

Pure lead is BHN 5. 1:20 alloy is BHN 10 Copper is BHN 40.

BP does not generally generate high enough pressures to deal with that at the top end of the equation. Lacking proper obturation we get gas cutting on the bullet and accuracy goes sideways. BP fouls a lot too, so there is a lot of requirement for synergy in bullet dimensions, which leaves the combination of lead and BP highly dependent upon obturation.

Another issue at hand is that lead is very ductile. Given a long nose which is unsupported, the least flaw can cause upset in symmetry of the bullet and this is exacerbated by quick twists.

I've read a number of articles were folks have explored the spitzer form for lead bullets and sometimes they are successful with smokeless powder but there is a limit to how far you can carry that with BP. BP bullets by definition of obturation are reformed during the firing sequence and there are finite limits on our ability to juggle the conundrums involved.

I rather think the Postell design, or others that are similar, fairly define the edge of the envelope in regards to the above. Plus there is the point made by Ranch. It's a good design for the velocity range.

A cross reference if you will, is the .22 LR bullet. Hasn't changed in meaningful fashion in over a century and you can bet your knickers if there was a competitive advantage to a pointy bullet in that cartridge someone would be doing it.

If I read you correctly you are saying that a fast twist can deform a soft ( lead ) bullet to the point that accuracy goes south?

excellent explanation - thanks!

It's a good thing I don't have to be a mathematician to shoot BPCR because if it did I'm dead before I start.

Yes, but I don't consider it an issue that pivots solely on alloy hardness and twist rate. The answer relates to the issues described in my previous post and more. The first two things that come to mind involve the geometry and measure of the rifling and in my opinion, the bullet mass form.

In simple terms illustrating the extreme; shallow grooves, large caliber and short bearing surface common to spitzer forms suggest the possibility of not only deformation of the bullet, but actual stripping of lead from the circumference of the bullet. Inertia plays here and there is a correlation between caliber and the amount of force required to impart angular momentum on the bullet for stability. More steeply pitched rifling compounds the required force.

I once fired a paper patched round ball (yep, I was bored!) from a .44 Mag rifle. I had done so previously with acceptable and consistent accuracy up to about 1,400 fps (chronographed). The target distance was 25 yards. On whimsy I thought it might be interesting to see what would happen with "more" powder. I don't recall the powder charge, but the ball crossed the Chrony as 2,400 fps and entirely missed the 2x3' target board at 25 yards. The throat and bore was quite leaded after the fact. Therein lies a an extreme illustration of short bearing surface, fast twist for the projectile, large caliber and a sick mind at work. I would guess if it had been a short lead hollow point it might have whistled along the way. Yee-Haw.....

You and me, both! I just figured out how to count past ten without embarrassing myself in public!

Ed

Ed, now you know why you were equipped with 10 more digits on your feet, 4 limbs, 2 eyes and ears and 2 brains of different size and location and one bung hole. Work it right and you can do differential calculus.

PS: One finger and an open mouth can serve as binary code as well...

Dan, Check out the slug on the Left,.......



An SMK nose, and a big classic greaser cylindrical body. .459 X 560 gr.

STILL haven't decided what to cast these out of,....but should be a LOT of fun to play with,the "Nose slumpers from hell".

What I WANTED was the 600 grainer pictured in the center,....a Leeth "Gordon" with an extra groove added. The 550 Gordon's on the right,......a GREAT bullet, IMHO.

I got the "SMK" one kinda' by mistake,.....figured I'd hang onto it, and someday play with it.

I could get arrested just counting change to a store clerk!

Ed

I think I now know why those 40 grain Sierra's that were engineered for the Hornet were disappearing midway to the target when fired at 3900 fps from my 22.250.