But Rob even a 5 thousand out of round bullet will be perfectly round when it leaves the barrel, but it might wobble a bit going down range
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But Rob even a 5 thousand out of round bullet will be perfectly round when it leaves the barrel, but it might wobble a bit going down range
Just checked a few boolits from my LEE 500-3R its average measurement is .4585 - nothing over .459 nor under .458Originally Posted by rfd
The 405 HB average measurement was .459 nothing under .4585 nor over .4595
So both of those were inside one thou out of round (surprised me)
This was with boolits already match weighed.
It seems to me that the problem (if there is one and that seems to be so) is either /or ....1) the deep lube grooves allowing distortion 2) the nose design is sensitive to wind .
I know there were crappy molds went out .....I had two of em - undersized by heaps .. and yes they might be difficult to cast consistently with because of the design - I would argue that, I have crook wrists and find iron or brass molds hard work where the alloy blocks light weight makes them easy to work with - but I have put all that aside because the molds I have are casting decent boolits with consistent weight and dimensions so it comes back simply to a design problem .....yes?
Now if I could just figure out how to monitor hits on my 500yard target with my mobile phone / tablet computer combo ..testing all this would be fun!
joe,
over on the bpcr forum under technical information, is an article by dan theodore that goes against all i believe.
he is extolling the virties of pointed bullets and stability and b.c. in our velocity range.
i believe he was shooting pointed bullets at raton creedmoor before he died, out of a fast twist 38/70.
it would be interesting to see where that would have led.
keep safe,
bruce.
Monitoring hits with an cellphone, iPad etc is a pretty simple thing to do if you get ahold of one of the Caldwell target camera's.
Long range rules, the rest drool.
Or use your phone with a hot spot and a laptop and do a face to face
That might work if you're somplace that has cell service... but the target camera is relatively inexpensive, will give you group measurements etc..
Long range rules, the rest drool.
Don I'd forgotten about those target cameras. I've been thinking this morning of getting a gong built to emulate the 600 yard bull out to the 9 ring, but maybe that camera is a better investment?
What do think if it now that you've had it a while?
Chris.
Kurt it's funny how many people you hear say that they don't worry too much about the bullets being a little out of round as they will bump up to be round. You are correct, there will almost certainly be some drag inducing wobble. There is nothing at all in the laws of physics that ensures that that bumped up, newly round, bullet will be dynamically balanced. It's pretty much a 100% certainty that it will not beBut Rob even a 5 thousand out of round bullet will be perfectly round when it leaves the barrel, but it might wobble a bit going down range
Interestingly though, my two Shiloh's in .40-65 absolutely love the my Saeco #740 bullets out to 300 yards even though that mold does not produce bullets as perfectly round as my BACO molds will.
Chris.
Chris when I go out on the range here, I take it along just like any other piece of equipment. It's a valuable tool. At 600 you don't need to use the receiver, the transmitter will have enough power to feed the picture. Beyond 600 the receiver is needed. It's just a handy thing to use anywhere from the muzzle to 1000 yards.
You can use a pallet covered with cardboard with a couple of 2 x4's for braces to hold it up right , or just set a couple of steel posts, and then a box of either the 600 yard targets or the centers, and off you go to the world of learning experience.
Long range rules, the rest drool.
the same thing happens when that bullet is run through a sizing die You cant compress lead, you just make it flow to a different place and this throws it out of balance at the high rpm these spin when they get pushed through the bore.Kurt it's funny how many people you hear say that they don't worry too much about the bullets being a little out of round as they will bump up to be round. You are correct, there will almost certainly be some drag inducing wobble. There is nothing at all in the laws of physics that ensures that that bumped up, newly round, bullet will be dynamically balanced. It's pretty much a 100% certainty that it will not be
Interestingly though, my two Shiloh's in .40-65 absolutely love the my Saeco #740 bullets out to 300 yards even though that mold does not produce bullets as perfectly round as my BACO molds will.
Chris.
more detail please! I have a phone with a hotspot and a laptop and cell reception - how do I set this up in the field - I want to shoot tomorrow this would be extremely helpful!
The driving band section will bump up to fit the bore, but the nose portion will still be out of round in relation to the driving bands. The bullet will be a camshaft.Kurt it's funny how many people you hear say that they don't worry too much about the bullets being a little out of round as they will bump up to be round. You are correct, there will almost certainly be some drag inducing wobble. There is nothing at all in the laws of physics that ensures that that bumped up, newly round, bullet will be dynamically balanced. It's pretty much a 100% certainty that it will not be
Chris.
I am not aware of this. Can you link this please. I would like to see if I get the same impression as you.
Thank you, CW
Chill Wills
This might be the bit you are looking for ? I googled Dan Theodore bullet stability
Some findings that were a bit of a surprise might shed some light on this bullet stability issue. A very good example can be shown by relating what bullet holes looked like at 1,000 yards through the target using two different rifles and bullets. One rifle is a 10-twist 38-72 and the other is a 12-twist 38-70. The bullets in question are a 1.496” long grooveless G3 design that weighs 405 grains and the other is a 1.54” long spire point what weighs 373 grains. One would assume using current common wisdom that the 405-grain, 1.496” long bullet would be more stable out of the 12-twist barrel than the lighter, longer spire point. Not at all! The 1.496” long bullet produces quite elliptical holes through the target even at 800-yards. It shoots great out of the 10-twist barrel. That seems reasonable. But here is the kicker, the 1.54” long spire point that only weighs 373 grains will punch round holes at 1,000 yards when launched out of the 12-twist barrel. Go figure! So what is going on? My current understanding is that the CP for the spire point is much closer to the CG than that distance for the 1.496” long, 405-grain 3G bullet. This phenomenon has been seen with a number of other bullet designs, calibers and twists also.
michael,
try www.bpcr.net/index-a.htm
if this does not take you to the page, on that site index is technical information.
go there, and look for a dan theodore article on bullet stability.
keep safe,
bruce.
I agree Kurt, that's why I don't generally size bullets ( except that I do sometimes size PP bullets down 0.001" ).
Thanks for the info Don.
Bruce, I think the key to understanding what Dan called counter to common wisdom is simply that the concept of stability as a function of bullet length and barrel twist is only very approximate. These formulae that people have come up with are only functions to approximately fit some data, there is nothing fundamental about them.
Chris.
chris,
i get what you say.
however i wonder if dan had shot that bullet every 100 of range out to 1000 what might have emerged.
my own experiments have shown that you can get a wobble at say 600 or 700, and then round holes again further out.
the distance where this happens is just about the line between transonic and true subsonic, or mach 0.8.
some nose shapes resist this better.
ways to increase b.c. include meplat diameter and ogive length and radius.
with our cast bullets, wa cannot have really pointy meplats because they are too hard to cast, and there is the added issue of releasing the boundary layer if we could.
ogive lengths cannot be much more than 1.5 calibres due to setback and the possibility of them bending as they slump.
transonic aircraft and missiles do not have sharp long pointy noses.
this is because it was discovered that airflow at those speeds was not smooth and regular on that shape.
among the preferred shapes is the ellipse, and something like the metford/money nose.
both economics and safety caused research into this.
certainly shortening the overturning moment will increase stability, and reducing pressure on the nose is an obvious way to do this.
but a bent nose will move the centre of mass from the physical axis and that will override all the gains.
the question remains open
keep safe,
bruce.
LEE vs LYMAN
Well fellers heres this mornings effort
ah ha you say !!!
this n proves two things (neither of which was the intention)(
1) ya better pay attention ALL OF THE TIME
2) me powder is gettin better as I go
so 6 shots with the LEE, one barrel warmer in the dirt - first at target is a good hit (my target is 10mm ply so I can hear em)
lets go to it - but hang on ????we getting dust in front of the target and no hit noise - theres a little tricky breeze up there and these guys on the forum have almost got me convinced that LEE boolit is a waste of time - I hear a hit on no 4 and that only reinforces their idea . Its a long drive over rough plowed ground to investigate so I went ahead with part two (continue shooting - look later) - the Lyman postell is gonna shoot straight but its gonna need some extra elevation so I screwed the sight up 38inches and shot one -----still in the dirt out front -- another yard up and we got a hit - goody!!!-- only got three left now so here they go - blowtube between shots - I can feel a little breeze trickin around down on the flat where I am - know it will be more at the target - but I didnt bother with a flag - what ya see is what I saw - four hits with the lyman postell strung sideways about 14 inches but nice vertical - theres two clear hits of that 500grain LEE absolutely dead sideways!! one in the main group and one up about a foot or so - another just clipped the bottom of the board if ya look close ........WTHeck.....is going on - yeah it might wobble some but clean as that sideways - nah!!!! .....think about this .....I take a walk around and find em about ten yards infront - there five boolit strikes on the hard ground right close together - woulda made a nice group no more than ten inches or so either way and further down is the lone strike from the first postell - I got that difference right - but - still puzzling - then the lightbulb - I used 2015 powder instead of 2017!!! hmmmmmpff.
So proved nothing really as far as testing that LEE boolit against the LYMAN - but the dang thing still seems to be shooting not too bad
Last edited by indian joe; 05-23-2018 at 10:19 PM.
Question for Bruce (and anybody else likes to help out)chris,
i get what you say.
however i wonder if dan had shot that bullet every 100 of range out to 1000 what might have emerged.
my own experiments have shown that you can get a wobble at say 600 or 700, and then round holes again further out.
the distance where this happens is just about the line between transonic and true subsonic, or mach 0.8.
some nose shapes resist this better.
ways to increase b.c. include meplat diameter and ogive length and radius.
with our cast bullets, wa cannot have really pointy meplats because they are too hard to cast, and there is the added issue of releasing the boundary layer if we could.
ogive lengths cannot be much more than 1.5 calibres due to setback and the possibility of them bending as they slump.
transonic aircraft and missiles do not have sharp long pointy noses.
this is because it was discovered that airflow at those speeds was not smooth and regular on that shape.
among the preferred shapes is the ellipse, and something like the metford/money nose.
both economics and safety caused research into this.
certainly shortening the overturning moment will increase stability, and reducing pressure on the nose is an obvious way to do this.
but a bent nose will move the centre of mass from the physical axis and that will override all the gains.
the question remains open
keep safe,
bruce.
If I take a CBE postell (quite traditional old style postell from what I can see) - its 550 grains, shallow lube grooves - and we delete the driving band and one lube groove - should make it about 490grain with three grooves instead of four - what would you expect that to do to stability at 45/70 speeds and mid range - 500 yards mainly???
Thanks
Joe
joe,
my assumption is that it would be stable.
assuming it is an 18" twist,
it will be a little more stable than necessary, which means that it will have a little more yaw of repose in flight.
with the proviso that dynamic stability cannot be calculated like gyroscopic stability.
if you can do it in a lathe, it might pay to shorten some that way for firing tests prior to spending money.
keep safe,
bruce.
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