question for williada or anyone else re transonoc and subsonic

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bruce moulds
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question for williada or anyone else re transonoc and subsonic

#1 Postby bruce moulds » Sun Oct 29, 2017 9:32 am

i feel a little reluctant to ask this as it is a bit off topic for this site.
a little preamble.
a desire to understand long range shooting and its history has led me to shoot black powder cartrige rifles for some years now.
the old dead guys shot out to past 1000 yds, and i have been shooting with fclass and tr guys at allour ranges, 300 to 1000, as well as some 100 and 200 comps.
the primary issue is that these bullets , starting at around 1300 fps are transonic, and become subsonic.
the issues that arise in these zones seem not to be understood by mainline ballistic studies or certainly not discussed much.
i have seen plots from the late 1800s demonstrating 1 moa vert capability, and i can approach that in certain weather conditions, but not in others.
i need to understand what effects wind direction and strength has on bullets at these speeds.
i think i have worked out stability issues by trial and error, and nose shapes that offer better b.c., and other issues to reduce drag where possible.
black powder can give amazingly low numbers for e.s. ans s.d. like 6 and 2.
would you be prepared to help me if you can? either privately or here if others are interested.
keep safe,
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880
http://youtu.be/YRaRCCZjdTM

bruce moulds
Posts: 2087
Joined: Sun Jun 19, 2005 4:07 pm

Re: question for williada or anyone else re transonoc and subsonic

#2 Postby bruce moulds » Mon Oct 30, 2017 12:10 pm

if anyone else understands these issues, please chime in.
if i should not discuss this here, please say so.
it could be o.k., as people discuss t.r. and b.r. here, and this is equally or more so related to fclass, particularly long range fclass.
keep safe,
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880

http://youtu.be/YRaRCCZjdTM

bruce moulds
Posts: 2087
Joined: Sun Jun 19, 2005 4:07 pm

Re: question for williada or anyone else re transonoc and subsonic

#3 Postby bruce moulds » Mon Oct 30, 2017 6:33 pm

there seem to be a few hits on this thread, & no one has said to leave it so here goes.
2 rifles, one 40 cal and one 45 cal.
using a fast twist in the 40 cal has allowed bullets of similar b.c. to the 45 cal, which from the muzzle velocity of about 1300 fps in both is approx 0.5 based on trajectory.
this is g1 drag model which is for a blunt spitzer
however nose shapes suggested by reading about trans and subsonic flight are elliptical (1.5 calibres long) and a shape known as the money nose.
the ellipse is very similar to the shape used by americans at the end of the era, up 'till 1912, and the money is similar to the metford long range nose used by the brits.
both bullets track similarly out to mach 0.8, when the ellipse demonstrates less drop.
smooth sided paper patch bullets exhibit less drop than grease groove bullets for obvius reasons.
to give an idea of flight relative to modern rifles, time of flight to 1000 yds is about 3 seconds, (spin decay has been measured at aberdeen proving ground in a 308 in 1 second, so there would be more in 3 seconds), and where a modern rifle might need around 20 moa comeup to 1000, the black powder bullet needs about 150 minutes.
stability Sg that seems to work best is more than 2.0, and in the 40cal 3.0 has experimentally proven best.
1.5 as used in modern rifles is good to 200 yds, but will probably fail between there and 1000.
bullets that are theoretically stable have proven to have wobbles at about mach 0.8, which went away by shortening the bullet.
none actually tumbled.
could there be a change of distance here between th centre of mass and an altering centre of pressure?
one would assume that this moment would shorten, and stability would simply increase.
these bullets exhibit about 2 moa spindrift, the 40 a bit more than the 45.
someone might comment on any of the above, as it is my observations with little understanding of why.
these rifles can group less than 1 moa at 100 with good loads, so they are not toys but rather serious tools.
when the loads start to come together, groups improve at longer ranges, but must be gauged by vert alone due to wind deflection.
this is where i need advice badly.
im "modern observations on rifle shooting" by edwin perry (free to read on internet archive), the author states that for the long range rifle about 1 point of elevation is required for every 5 points of windage required on the sight. (aerodynamic jump?)
my understanding of this in modern rifles is about 1 to 10, but that could be wrong.
can anyone comment here. possibly a time of flight thing?
i also think that this elevation shift in side winds is greater proportionally at closer ranges than longer ranges.
this could explain in part the difficulty in holding good vert.
it seems fairly easy to do this in constant condition.
i really need advice here.
add to this when the varying condition is a frontal or rear fishtail going across centre.
head and tail winds also have elevation effects.
how do you juggle this in with elevation due to side winds.?
is there a sudden change of influence from one to the other, or is there a blending in?
keep safe,
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880

http://youtu.be/YRaRCCZjdTM

williada
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Re: question for williada or anyone else re transonoc and subsonic

#4 Postby williada » Mon Oct 30, 2017 6:55 pm

Bruce I am having a breather having spent the last few years giving personal assistance to a few in their quest to go to Canada and perform in Oz, and also having a second heart op last year. Just doing club stuff these days and keeping the wife happy. Others may be happy to add comments, so I kick off discussion with thoughts below for them to follow up. Hope you understand.

Ballistic studies moved on from black powder and tried to keep out of the transonic zone because it was too hard to quantify and predict a precise point of impact at long range with the pitching and yawing caused by the sound barrier in the transonic range creating a shockwave. It is categorized as dynamic instability because of the pitching and yawing and causes a loss of BC. It’s no good looking to use longer bullets because they pitch and yaw more. A shorter bullet with a larger diameter might resist the instability to a greater degree with increased radial torque and if you hope to increase the gyroscopic stability with a faster twist rate to keep the axis of the bullet in a straight line in this zone the lead yields too easily and might strip. I think it is commonly accepted that target accuracy disappears completely at about 1450 fps for black powder setups with lead bullets for this reason. Remember too, the speed of sound varies with temperature and a load on the edge might be right one day and tip over the next. Assume we could a tad over stabilize the bullet thinking it will assist in the transonic zone, but there is a greater divergence with the trajectory at long range because the axis of spin is maintained with the axis of the barrel. In this scenario the bullet may not be tractable i.e. it does not follow the bending trajectory and this is particularly relevant to high angle shooting which black powder imposes in order to hit the target at long range with slow velocity.

In another scenario, ask yourself whether a subsonic trajectory which is very accurate and nose shape is of little consequence, could you hit 1000 yards? If you could, the incoming projectile would have a very steep angle and would put markers at risk and tear downward chunks out of the target. Anyone for electronic targets?

There are some other issues to consider.

People who have shot black powder competitively would know a great load can go off within the hour due to fouling hardened by a humidity decrease and will mask group analysis particularly at a transonic speed as I see it to see what is happening. Shooting the stuff is certainly a black art as much as science. The lead bullet is a delicate thing. The best projectiles were almost pure lead with a temper of about 1-25 i.e. one part tin to 25 parts lead. These days the firm “Swiss” makes the best black powder as others are at times inconsistent. When we were young we used to make our own and my grandfather used it in a splitting gun to split logs in the bush. The best charcoal to use was willow. I won’t say any more about ingredients to give the wrong people ideas.

In order to gain greater mass and weight compared to a ball, conical bullets were made trying to cast perfect bases because they were a key factor in controlling in-bore yaw and tip orientation so critical to the external trajectory and accuracy. The best bullets were made to exact bore diameter and were bumped up on ignition to expand the base to fill the groove for seal. Quite the opposite as to what jacketed bullets do in modern chambers. The momentary force or inertia on a modern bullet is much greater and impacts greatly on muzzle oscillation which determines nodal shape when tuned due to higher pressures not only from the smokeless powder but how the jacketed bullet engages both the bore and lands at the same time and explains why Pope could produce fine round nodal groups early last century with black powder at short range. One assumes the dynamic stability of the projectile is better on leaving the muzzle in black powder with reduced nutation and precession damping out with distance. Of course projectile oscillation can occur with forces at right angles to motion at either end of the projectile from different sources but these occurrences are a force of short duration whereas the gyroscopic force is constant and decays little with distance. At the end of the trajectory the nose oscillates in a wider arc and with a decay in velocity the projectile loses static stability created by gyroscopic forces.

Importantly there was a bit of forward movement of the lead projectile running on the top of the rifling (bore) so as to keep it concentric with the bore and not upset to it for smooth take-off when the base expanded. Gain twist barrels added to performance of delicate lead bullets and their prescriptive set-up. My use of gain twist with jacketed ammunition suggests it is a minor disadvantage because the set-up is poles apart in modern rifles. I have discussed this before.

The black powder target barrels were 32- 37 inches long to maximise velocity from the low pressure black powder but also had slow twist rates say 1-24, for conical bullets and not to be confused with ball requiring less stabilization at 1-48. The ignition variables were reduced by high density load and hot primers.

No doubt these things could shoot up close as I posted a picture a few years back of Harry Pope’s 10 shot group at 200 yards early last century, all practically through the one hole. Black powder does have low ES in the right hands and modern load development principles and the effect of wind vectors do apply before the projectile becomes transonic; and like the modern projectile, the masks have to be removed to see the essence of the real group. Some lead bullet principles can be applied to jacketed ammunition others cannot.

The key problem with lead bullets is base mutilation which causes the bullet tip to change orientation and this affects its flight usually by increasing it angle of attack. Fouling can chew at the edges of the base. It’s interesting that bench rest shooters with flat based bullets like clean barrels. Warren Page once said, “cleanliness is next to Godliness”.

If you think about Pope’s record groups from muzzle loaders, the fouling in the barrel was pushed down out of the way relatively speaking because at the breech, the fouling sat in the groove below the projectile which sat on the lands. In addition, the long length of the barrel enabled most of the combustion residues to fall out several inches before the muzzle which was also taper lapped to caress the delicate lead back in to shape as it passed through the main fouling zone into the most important section of the barrel for accuracy which was relatively cleaner. Of course the lubrication of the lead bullets was an important element in countering fouling too. Perce Pavy used to say to me, accuracy is all in the last six inches. Could this be a reason slow burning modern powders are well suited to long barrel? It’s also a reason why I use the hotter burning powder with the 7mm such as 2209 as compared to 2213 or 2217 and suggested using it to an aspiring squad member about 3 years ago. I could see problems with long strings for obvious reasons. In previous posts I have mentioned the benefits of jammed projectiles, warm primers, firm neck tension etc in relation to ignition, barrel lift and cleaner burn. I have advocated round robin tests of five shot for five or six groups spread horizontally in load development to reduce the masking affect of fouling with each shot 45 seconds apart.

With black powder the humidity is critical and affects the hardness of the fouling. That is why a good group may not be duplicated in an hour’s time if the air temperature or barrel heat dries the barrel out. Modern black powder enthusiasts have a breathe tube inserted between shots to blow air from their lungs which is moister down the bore. It’s not to blow the smoke out! By keeping the fouling soft the scores are improved. Unlike smokeless powders, visible water as a bi-product of combustion with black powder is not a problem for long strings. In contrast a jacketed bullet produces more heat. Heat does destroy small vibration. Although more vibration is created with jacketed bullets along with muzzle oscillation, faster strings may be better than slower ones if conditions are constant and you can get good shots off.

People may think of using a big calibre like a 45-70 to buck conditions with black powder, but if we think about it, a lighter projectile uses less powder and therefore produces less fouling for a long string. The effects of fouling in black powder can increase group size by a greater amount than the small variances created in conditions that the heavier pill is thought to counter. It’s all about trade-offs, but masks have to be removed for objective analysis.

So on balance, with lead bullets, I think you can only keep SD’s down and get what you get. With low SD black powder can achieve, compensation tunes are not required and are not a panacea for less than predictable motion and turbulence in the transonic zone. Projectiles with a greater diameter may be of benefit to increase radial torque with the fastest twist rate lead can take. Just might have to sacrifice length if too heavy because of fouling issues. There is a lot to optimise. You could investigate the actual BC’s. I used to confirm BC with the use of two chronographs. I now have a Canadian produced one which can be set at safe distance within several feet of the trajectory. This is ideal for setting up under the target and would suit black powder experiments at distance.


Hope I have been of some assistance, David.


bruce moulds
Posts: 2087
Joined: Sun Jun 19, 2005 4:07 pm

Re: question for williada or anyone else re transonoc and subsonic

#6 Postby bruce moulds » Mon Oct 30, 2017 7:47 pm

david,
thank you for the reply.
i should have qualified shooting method, but thought it might be of little interest.
fouling is the great killer of accuracy as you say, and blowtubing is one way to deal with it.
american long range riflemen wiped their barrels, first with a fisher brush soaked in water, then several dry rags, some following with a lightly oiled rag.
this is now common practice in some form or other, often using soluble cutting oil as the solvent, as it gives a consistent barrel condition whatever the humidity or temperature, compared to blowtubing.
consistent barrel condition is what it is all about.
getting 2 sighters off plus 10 to count can keep you on your toes wiping, wind reading, and shooting!
a fairly standard alloy for long range bullets is 16:1.
i have gone as hard as 12:1 with bullets patched to bore (not groove) diameter with success, said bullets bumping up to take the rifling well.
the idea of this is to minimize nose slump in order to maximize b.c.
getting a long range bullet up to a full 1400 fps is about it with black powder.
express rifles with lighter bullets were a different story, and they had to shoot dirty.
from what you say, i could be getting some buffeting etc due to transonic issues, and that these might still not be fully understood by science.
i would like to beilieve that this is not the black art that many think it is.
i think i can get these cartridge rifles to shoot, but issues like the above make it difficult.
understanding how if possible to calculate aerodynamic jump would make proving or disproving things easier.
is there a way to do this.?
it seems that you need to know the drag coefficient. how is that calculated.?
with regards safety in the butts for markers with these bullets, they come in at about 3 degrees at 1000 yds, hitting the bottom of the holes in the backstop made by smokeless bullets - quite safe with sensible loads.
it is known that maximizing the velocity gives better vert than loads starting subsonically.
this in itself could offer some information, as it is ythe opposite of what one might expect, as the bullet has more transonic flight.
keep safe,
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880

http://youtu.be/YRaRCCZjdTM

bruce moulds
Posts: 2087
Joined: Sun Jun 19, 2005 4:07 pm

Re: question for williada or anyone else re transonoc and subsonic

#7 Postby bruce moulds » Mon Oct 30, 2017 7:50 pm

david thanks for the link.
keep safe,
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880

http://youtu.be/YRaRCCZjdTM

bruce moulds
Posts: 2087
Joined: Sun Jun 19, 2005 4:07 pm

Re: question for williada or anyone else re transonoc and subsonic

#8 Postby bruce moulds » Mon Oct 30, 2017 8:05 pm

a comment inadvertantly not included.
i usually compare my max, min , and average deflections with tr shooters.
it seems that the old dead guys bullets have about 3x deflection of a 308x155 gn load while transonic, but only about 2x when subsonic.
this suggest a significant reduction in drag between the 2 zones.
i thought nose drag was insignificant at subsonic velocities, but the fact that the elliptical has less drop in that zone suggests that drag profile is also important here.
keep safe,
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880

http://youtu.be/YRaRCCZjdTM


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