GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: ballisticboy on September 08, 2021, 07:53:29 PM
-
This is a first look at what may happen if slugs have to be made from an alternative to lead. The material I have used for the modelling is tin. The slugs are all .22 calibre based on a commercial design, with a hollowpoint nose just short of one calibre long, and a cylindrical aft portion of different lengths to give different slug masses. The design is fairly standard for slugs, with many of the currently available lead slugs being very similar in shape and size and can be seen below.
(https://hosting.photobucket.com/images/oo221/rsterne/Image1.jpg?width=1920&height=1080&fit=bounds)
Slug overall lengths varied from 6.7 mm to just over 11 mm. Slug masses for the tin slugs varied from 12 to 24 grains, while the identical slugs made from lead varied from 19 to 37 grains. The muzzle velocity for all the slugs was fixed at 950ft/sec. The use of a fixed muzzle velocity is an initial starting point.
I could have used a fixed muzzle energy, but some of the tin slugs then end up travelling at supersonic velocities or some of the lead slugs would be travelling very slowly. To start the examination I wanted to introduce some fixed parameters to simplify the modelling which already required intensive production of many types of data files.
To produce an error at the target end of the trajectory, I first used an initial yawing rate of ten radians per second on each of the slugs. The maximum range in all cases was 75 yards.
The first job was to calculate the mass, centre of gravity and inertial moments for each of the slugs. These characteristics are necessary for the rest of the input data files and for the stability calculations. The next job was to predict the aerodynamic properties of each slug using the calculated centre of gravity. The aerodynamic prediction program is a specialised version of a program created many years ago, an early version of which is on the JBM website. The accuracy of the predictions when compared to known values was /-10%. For the slugs in this exercise, even if the errors are larger, the comparisons between the tin and lead slugs should be valid as the same aerodynamics are being used.
For rifle bullets, it is generally considered that a stability factor of 1.5 is the minimum required for good performance. For this reason, I calculated the barrel twist rate needed to have a stability factor of 1.5 for each slug, both lead and non-lead. The calculated twist rates needed for the required stability factor were then used in the trajectory modelling for each slug. The table below shows the slug lengths, mass and barrel twist rates for both the tin and lead slugs.
(https://hosting.photobucket.com/images/oo221/rsterne/table_1.jpg?width=1920&height=1080&fit=bounds)
The table immediately shows up some problems for shooters and designers. For a given length of slug the tin one is much lighter, which is to be expected, and it requires a higher twist rate for the same stability factor. For the gun owner this means that unless he changes his barrel for one with a higher twist rate a shorter slug in tin will be required compared to a lead one, which will make the mass loss even greater. For example, a gun with a 22 inch twist rate will only be able to fire tin slugs of around 12 grains instead of the 25 grains for a long lead slug which could be used previously. The gun will also need adjustment to reduce the muzzle velocity if supersonic speeds are to be avoided.
There are also problems for slug manufacturers as well. Tin slugs will need increased barrel twist rates if the slug mass is to be preserved. Take a 24 grain slug mass as an example. A 24 grain lead slug will only need a 23 inch twist rate, whereas a 24 grain tin slug needs a 13-inch rate. Selling a slug which requires such a high twist rate to the general public, as opposed to enthusiastic experienced shooters willing to change their barrel, could prove challenging.
The graph below shows how the necessary twist rate varies with slug length for both the tin and lead slugs.
(https://hosting.photobucket.com/images/oo221/rsterne/Image2.jpg?width=1920&height=1080&fit=bounds)
If the slug mass is of interest, the comparison for tin and lead slugs is shown here.
(https://hosting.photobucket.com/images/oo221/rsterne/Image3.jpg?width=1920&height=1080&fit=bounds)
Remember, these numbers are for slugs fired at 950ft/sec. For higher muzzle velocities, faster twist rates will be needed.
For each slug, both lead and tin, two trajectories had to be run, one with no yaw rate on the slug and one with the 10 radians per second yaw rate at the start of the trajectory. There was a slight problem in that the modelling suggested that the shorter slugs suffered from a dynamic instability leading to increasing yaw and a slight spiralling effect at the end of some trajectories. To overcome this, a straight line was fitted to the error calculations (initial yaw rate errors give a linear increase in error with range). The slugs are probably not going to be dynamically unstable in real life, it is just very difficult to predict it accurately, particularly for small projectiles.
The predicted group sizes at 75 yards range for both the tin and lead slugs as a function of slug mass is shown here.
(https://hosting.photobucket.com/images/oo221/rsterne/Image4.jpg?width=1920&height=1080&fit=bounds)
The group sizes look very similar. Looking at the group size as a function of slug length gives an easier comparison.
(https://hosting.photobucket.com/images/oo221/rsterne/Image5.jpg?width=1920&height=1080&fit=bounds)
There are actually two curves there, but the lead one lies directly underneath the tin curve, something we would not expect. It would appear that with the same initial error, stability factor and muzzle velocity, slugs of the same length will give the same group size.
The group size results in tabular form for a fixed initial yaw rate are shown below.
(https://hosting.photobucket.com/images/oo221/rsterne/table3.jpg?width=1920&height=1080&fit=bounds)
This exercise is supposed to be concentrating on projectile error sources and looking at how the slug reacts. With the different twist rates for tin slugs, it seems unlikely that projectile based error sources would give the same initial yawing rate as the slug leaves the barrel. To take account of this, the 10 radians per second yaw rate was kept for the slug requiring the slowest twist rate and all the other slugs yaw rates were adjusted in proportion to their barrel twist rates. The resulting initial yaw rates for each slug are shown below.
(https://hosting.photobucket.com/images/oo221/rsterne/table2.jpg?width=1920&height=1080&fit=bounds)
The group size results are now very different for tin and lead slugs. Below you can see the group sizes at 25, 50 and 75 yards for the lead and tin slugs.
(https://hosting.photobucket.com/images/oo221/rsterne/Image6.jpg?width=1920&height=1080&fit=bounds)
In this case, for a given slug length the lead slug always gives smaller groups than the equivalent tin slug, about 20% less. This is more in agreement with the results of a pellet study comparing pellets made of zinc and lead. The group sizes as a function of slug mass at 75 yards are shown here.
(https://hosting.photobucket.com/images/oo221/rsterne/Image7.jpg?width=1920&height=1080&fit=bounds)
According to this chart, a lead slug of much greater mass can be fired for the same group sizes as the shorter, much lighter tin slug. Finally, for shooters with a fixed twist rate, the diagram below shows how the group size for tin and lead slugs varies with twist rate for the fixed stability factor.
(https://hosting.photobucket.com/images/oo221/rsterne/Image8.jpg?width=1920&height=1080&fit=bounds)
Below are the group size results for twist rate related yaw rates at 75 yards in tabular form.
(https://hosting.photobucket.com/images/oo221/rsterne/table4.jpg?width=1920&height=1080&fit=bounds)
So what does it all mean? These are some initial thoughts, there is a lot of data to look at and a lot of observations which can be made. For shooters, unless you change the barrel on your gun to have a much faster twist rate, you will only be able to use much lighter and shorter slugs in tin than you could in lead. To avoid the new tin slugs travelling at supersonic speeds, you will also have to reduce the muzzle energy of your gun. Tin slugs of the same mass as some lead slugs can be used, but they may be too long to fit in the magazine and will need an even higher twist rate.
For slug makers, the problem will be how do you make a tin based slug which can use pellet type twist rates without going ultra short and light. Making a tin slug the same mass as a lead slug can be done, but it will be much longer and may well not work with standard twist rate barrels or fit in magazines.
There are still lots of variables which can be changed such as different stability factors, different error sources in the slugs, different muzzle velocities or constant muzzle energies. Each one could change the resulting group sizes, but tin slugs will always need much higher twist rates in the barrel than the equivalent length or weight lead slug.
-
Thanks for taking the time to do all those calculations and write the article, Miles.... Lots there to think about, for sure.... With some parts of the World getting rid of lead for projectiles, this could become increasingly important.... As you say, unless you are replacing lead with tin directly (at only 65% of the weight), accuracy is likely to suffer, and even then a faster twist rate may be required....
One thing we need to remember, regardless of the projectile, using too fast a twist rate is generally not the best for accuracy.... Not as critical as too slow a twist (unstable and tumbling) to be sure.... but it emphasizes any slight imperfection in the projectile, increasing initial yaw, and ultimately group size....
Bob
-
Great read, I have been experimenting with cast tin and lead slugs, your calculations look to be in the ballpark with my initial test results.
Inspired me to go cast up some of my latest .177 slugs in tin for my next range experiment. I still have to do further testing in the larger calibers that I first experimented with over a year ago, so many options so little time ;)
Have you run the numbers for a BBT say in .22, I have had decent results with them in tin with my custom Airforce Escape UL, worth more testing IMO.
-
So what does it all mean? These are some initial thoughts, there is a lot of data to look at and a lot of observations which can be made. For shooters, unless you change the barrel on your gun to have a much faster twist rate, you will only be able to use much lighter and shorter slugs in tin than you could in lead. To avoid the new tin slugs travelling at supersonic speeds, you will also have to reduce the muzzle energy of your gun. Tin slugs of the same mass as some lead slugs can be used, but they may be too long to fit in the magazine and will need an even higher twist rate.
Interesting. I have limited knowledge to figure out the models but it is really good information we "need to start thinking about".
I see the "drawbacks" you identified as advantages except for more drag in the bore and less expansion or metplat. I'm thinking slug slingers now, probably more than 12 FPE. Magazines shouldn't define the gun. They will just have to make them longer. Future technology will eventually catch up with problems that we are thinking about now.
Like how will we use airguns without lead, depleted uranium, meteorite or tungsten and if it is tin how do we design the twist and loading port. They would probably have better BC, maybe closer to PB bullets. I'm thinking some PB barrels might have a good twist. Even some PB magazines can be used. I'm thinking of a design where you could incorporate one in the traditional PB position for loading. I think with problems come innovation.
Although this is a single shot it is probably using this Tin technology already.
https://www.altaros.cz/en/pcp-rifles/119-altaros-m24.html (https://www.altaros.cz/en/pcp-rifles/119-altaros-m24.html)
(https://www.altaros.cz/863-large_default/altaros-m24.jpg)
Sorry this is not a plug and I don't have any stake in the company. I just think it's cool.
-
With the complete ban of lead projectiles seeming inevitable (at least some day-not talking about current politics in the slightest!!); this information is invaluable.
Many, many thanks; much appreciated.
Jesse
-
Great read, I have been experimenting with cast tin and lead slugs, your calculations look to be in the ballpark with my initial test results.
Inspired me to go cast up some of my latest .177 slugs in tin for my next range experiment. I still have to do further testing in the larger calibers that I first experimented with over a year ago, so many options so little time ;)
Have you run the numbers for a BBT say in .22, I have had decent results with them in tin with my custom Airforce Escape UL, worth more testing IMO.
I haven't run any BBT's in tin, just lead. I was concentrating on the usual slug design to start with and can move on to alternative designs in the future. There are still many more questions to be answered, which will hopefully eventually help with non-lead slug designs and their use.
-
There is no no viable substitute for lead, and there never will be.
Tin is harder and too light, and way too expensive.
Copper and brass way too hard. So we end up with nothing or something expensive and not as working.
Sabots and tungsten maybe. That works in my guns but I don't think the authorities want us to use armor piercing projectile?
These green folk have no idea what is really harmful to people, or the environment, or do they? Lead is so heavy that it sinks to the bottom if in water, but plastic in the other hand.
Marko
-
I use tin projectiles when pesting, as I leave the carcass for the critters higher on the food chain to get a free lead free meal. Not a fan of plastic either, melts to the barrel at higher powers, and there is enough of it in the environment already.
-
Pure tin is about BHN 10, so certainly not too hard for use in an airgun.... and it melts at a lower temperature than lead, so easy to cast.... It is softer than 5% tin in lead, for example.... Expensive, yes.... ::)
Bob
-
There is no no viable substitute for lead, and there never will be.
Tin is harder and too light, and way too expensive.
Copper and brass way too hard. So we end up with nothing or something expensive and not as working.
Sabots and tungsten maybe. That works in my guns but I don't think the authorities want us to use armor piercing projectile?
These green folk have no idea what is really harmful to people, or the environment, or do they? Lead is so heavy that it sinks to the bottom if in water, but plastic in the other hand.
Marko
Agreed. Not to detract from the science here which has no political motive. The lead vs tin argument really IS a politically correct action (one that doesn't make sense or really has no ground in reality but enough argument to gain followers who feel good about the rhetoric and promote it regardless). For us in the U.S.A. I think we have to use maybe California as a thermometer in this case. I have no idea. Have they banned lead there or anywhere? Has any country banned it?
Tungsten is too expensive too. Instead of shooting expensive tungsten a friend of mine loads pea gravel in his PB shotgun shells to comply with waterfowl hunting laws. Gets a new barrel when it wears out. It's cheaper even when you figure in a new barrel. And that's the craziness of these laws too.
So, hey, there's a ban on lead shot there. I think that is US federal.
-
Tungsten is too expensive too. Instead of shooting expensive tungsten a friend of mine loads pea gravel in his PB shotgun shells to comply with waterfowl hunting laws. Gets a new barrel when it wears out. It's cheaper even when you figure in a new barrel. And that's the craziness of these laws too.
I seem to remember from the tank ranges that there are pollution problems with tungsten as well. When I was looking at using mini tank ammunition type long rods for sniper ammunition, I asked some of the management to find out if it was allowed, but I was retired before there was any answer.
-
Tungsten is too expensive too. Instead of shooting expensive tungsten a friend of mine loads pea gravel in his PB shotgun shells to comply with waterfowl hunting laws. Gets a new barrel when it wears out. It's cheaper even when you figure in a new barrel. And that's the craziness of these laws too.
I seem to remember from the tank ranges that there are pollution problems with tungsten as well. When I was looking at using mini tank ammunition type long rods for sniper ammunition, I asked some of the management to find out if it was allowed, but I was retired before there was any answer.
I think people can find problems with any substance. Although I found this:
"Some forms of tungsten can move readily though soil and groundwater under certain environmental conditions. ... Scientists have shown that exposure to tungsten can stunt the growth of plants, cause reproductive problems in earthworms, and trigger premature death in certain aquatic animals."
https://phys.org/news/2009-01-health-environmental-tungsten.html?&cf=1 (https://phys.org/news/2009-01-health-environmental-tungsten.html?&cf=1)
Well, maybe I agree to a certain extent. I think earthworms "biology" is already messed up enough!
-
Heavy going, but insightful!
How do I vote this thread up?
-
Heavy going, but insightful!
How do I vote this thread up?
It used to show in the header bar along the top of the page, but not seeing it??
Edit-looks like that function is completely turned off here....
Jesse
-
I had no idea that group size could be calculated/predicted. I am surprised that the best slug lengths are so short. Is that with the stability factor at 1.5 for all cases; or a fixed barrel twist?
-
The stability factor is 1.5 in all cases.... The calculations are assuming a given initial yaw, caused by imperfections in the slug, caused by the CG not being in the center of the form.... As the slug exits the muzzle, and the slug changes from rotating around the center of form (the center of the bore) to rotating about the CG, it yaws due to gyroscopic precession.... The longer the slug, and the faster the twist rate, the greater the initial yaw.... The more perfect the slugs, the less the initial yaw, of course.... Changing the relationship between the CG and the CP of the slug will change how that yaw damps out (the slug goes to sleep) or increases (tending to developing a spiral).... again all related to velocity and twist rate....
Bob
-
I thought that a longer slug provides a better lever for the correcting moment, to force the projectile to follow its projectile with less yaw? Assuming the center of form and center of mass are also further apart.
Are rifle bullets "long and pointy" only for high BC? Would shorter ones be more stable; and shoot smaller groups (at the expense of effective range)?
Obviously, an out of balance slug can upset things - all else being equal.
-
Miles can give you a better answer to your first question....
Regarding the second, yes, long bullets can have a better form factor, but a lot of their higher BC comes from their greater SD.... However, they do require a faster twist, and in a crosswind they will have greater "aerodynamic jump" (vertical deflection from that crosswind), and likely greater "throwoff" from bullet imperfections as well.... As the bullet turns to face into the "relative wind" (the vector sum of its forward velocity and the crosswind velocity) that yaw causes it to deflect upwards or downwards, depending on the direction of the crosswind and the direction of the twist.... and also depending on if the CG is ahead of or behind the CP.... This causes groups to slope in gusty winds, rather than being strictly horizontal.... However, if the BC of the shorter, lighter bullet is lower (as we would expect), it's crosswind drift will be greater....
As you can see, in real world conditions, a long bullet with a good BC has some advantages (flatter trajectory, less drift).... while a short bullet with a poorer BC, but shot in a slower twist barrel, has other advantages (less throwoff and jump).... This balancing act between long and short bullets is one of the reasons you seldom find bullets with extreme length/diameter ratios being use in benchrest competitions.... The upper limit is about 5:1 (with 4:1 being more common), and the lower limit is probably about 2:1 (to get a decent BC).... A lot of really great PB bullets are about 3-4 calibers long, but many of those are too high an SD for airgun use, because of our low pressures.... In addition, their advantages may be greater when Supersonic, so our "ideal" L/D ratio may well be 2-3 calibers long, (maybe even less?)....
The bottom line is, you still have to find the one that works best in your barrel, and/or vice versa.... Miles may have additional comments as well....
Bob
-
So was the Lone Ranger onto something with his silver bullets ??? or am I confusing that with werewolf hunting :-\ Either way I'm on a tin & lead budget.
-
OOPS: Meant trajectory for bolded projectile.
I thought that a longer slug provides a better lever for the correcting moment, to force the projectile to follow its projectile with less yaw?
-
Thanks Bob,
Good point about bullet length advantage shifting as the speed of sound is exceeded. As such, airgun slugs are more like handgun bullets than rifle bullets.
-
Absolutely correct.... However, the influence of a high SD on the BC still applies, as they are directly proportional.... The problem is, that in order to obtain a velocity in the mid 900s, there is a limit on the maximum SD you can use, based on the product of the pressure and barrel length.... For a 24" barrel, and assuming you can get the FPE up to 50% of the theoretical maximum (ie my "lofty goal"), there is a maximum SD (and hence bullet weight) for a given pressure to hit 950 fps....
(https://hosting.photobucket.com/albums/oo221/rsterne/PCP Internal Ballistics/.highres/BulletWeightvsCaliberfor950fps_zps00e63184.jpg?width=1920&height=1080&fit=bounds) (https://app.photobucket.com/u/rsterne/a/59674f5e-e0e0-494c-b053-58726736f031/p/ac4c2667-ae88-4242-8763-deeb34b754ac)
The lower chart is simply an enlargement of the upper one.... It would be a rare PCP that would be able to achieve 950 fps with the above bullet weights.... For cylindrical bullets, the length is proportional to the SD, which means that to shoot a longer bullet at 950 fps you need more pressure, regardless of caliber.... All the bullets in the photo below (note the similar lengths) have a Sectional Density of 0.17....
(https://hosting.photobucket.com/albums/oo221/rsterne/Bullet Casting/.highres/Sectional Density_zpsmaptgb6x.jpg?width=1920&height=1080&fit=bounds) (https://app.photobucket.com/u/rsterne/a/8a1f0fa0-fce3-4227-8f61-b397601e0866/p/c950ae97-dcab-4cdb-96ce-c702eb22367e)
That matches the blue line (3000 psi) in the above graphs.... For the larger calibers, these are very much shaped like a pistol bullet, only for the smaller calibers do they look more like a rifle bullet.... Sorry to get a bit off topic here.... :-[
Bob
-
Thanks Bob
All things considered, what can be achieved with just 3000 PSI peak pressure is pretty impressive. It is not far below light black powder muzzle loader ballistics.
-
I thought that a longer slug provides a better lever for the correcting moment, to force the projectile to follow its projectile with less yaw? Assuming the center of form and center of mass are also further apart.
Although it will depend on the projectile shape to some extent, a longer projectile will tend to have a longer distance between the aerodynamic centre and the CG. On an aerodynamically stable projectile this will give more stability. Bullets are unstable, hence they tend to become more unstable as they get longer. With gyroscopic stability, there is also the problem that the transverse inertia gets bigger at a faster rate than the rotational inertia, further reducing gyroscopic stability. As a result, faster twist rates are needed.
-
With gyroscopic stability, there is also the problem that the transverse inertia gets bigger at a faster rate than the rotational inertia, further reducing gyroscopic stability. As a result, faster twist rates are needed.
Yes, Miles. If you were stuck with one barrel, then long projectiles could easily drop below your imposed stability factor of 1.5. But, for this exercise you already sated that all projectiles would be fired from whatever twist barrels would be required to yield 1.5 stability factor, at a muzzle velocity of 950 FPS.
The reason for my question was that your chart for predicted group size seemed to favor much shorter projectiles that I expected, even when barrels that has fast enough twist to provide a stability factor of 1.5 would be available.
-
This might explain why my regulated Bandit sometimes has great groups and sometimes doesn't with my Dynamic TM-1 .177 9.5 grn tin pellets. In one 9 shot magazine I might get three different size groups of three shots each. On the other hand my Daisy 901 fires the H&N 6.64 grn pellets with extreme accuracy at 9-10 pumps. A few days ago I ordered some 19.91 grn .25 H&N green I want to test in my Eagle Claw. When this storm clears I want to see if I get better groups with the Bandito using the copper plated H&N Barracuda Power 10.65 grn pellets.
If heavier tin pellts/slugs become available I would gladly replace my barrels with an appropriate twist rate. I just don't know anything about getting a "custom" barrel.
-
This thread is about slugs, not pellets, however there is another by Miles in a Sticky below you may find interesting....
Bob
-
This thread is about slugs, not pellets, however there is another by Miles in a Sticky below you may find interesting....
Bob
Thank you, I'm reading it now.
-
Yes, Miles. If you were stuck with one barrel, then long projectiles could easily drop below your imposed stability factor of 1.5. But, for this exercise you already sated that all projectiles would be fired from whatever twist barrels would be required to yield 1.5 stability factor, at a muzzle velocity of 950 FPS.
The reason for my question was that your chart for predicted group size seemed to favor much shorter projectiles that I expected, even when barrels that has fast enough twist to provide a stability factor of 1.5 would be available.
It is probably down to the relative increases in aerodynamic moments compared to inertial moments and their effects on the yaw wave lengths, which tend to be longer on longer projectiles. As a result, longer projectiles will be slower to react to yaw angles than short projectiles and thus have larger dispersion and group sizes.
-
Thanks, Miles
While your calculated dispersions seemed to favor shorter slugs; the dispersions for the longer ones seemed to top out near 1 MOA. Hardly something to gripe about.
I think that slug yaw at the muzzle can be greatly reduced by means of an effective air stripper. This should make a difference in the precision on target; else they would not be so common for airguns. Or am I missing something? Perhaps, that air strippers help more with pellets than slugs.
-
While the muzzle blast can certainly cause yaw, and that may indeed be reduced by a good air stripper.... the type of yaw that Miles is calculating is a reaction to bullet imperfections.... When the bullet is released from the bore, it changes from rotating about the center of form (axis) of the bullet to rotating about the CG.... If the CG is not exactly on the center of the bullet, when the bullet changes its axis of rotation, it yaws in reaction to that.... It is that initial yaw Miles is using, as I understand it....
Bob
-
Thanks Bob
This is where projectile quality comes in. Poor ammo will shoot poorly. Also, design can have a major effect on the risk that the center of mass might be slightly offset, such as dual core for military bullets.
All of the above makes me wonder how benchrest shooters ever achieve quarter MOA groups. Sure, if it is 3 or 5 shots, then luck will occasionally land tight groups. Not for more shots; and not if they can repeat it.
-
Miles would be the guy to ask about that.... I would like to know as well what is needed to produce consistent fractional MOA groups..... I presume extremely well made bullets is the key, but are there other factors as well?....
Bob
-
While there are dozens of factors affecting precision, in the end for the projectile it all comes down to two main groups, how the projectile is launched from the barrel and how the projectile reacts to how it is launched. At short ranges the first group of factors is more important than the second, but as ranges increase, so to do the importance of the second group.
If a projectile leaves the barrel perfectly with no yaw or yaw rates, it will fly straight and consistently to the target and give good precision. This is the method used for most airguns or small arms, in that they try to minimize any problems through precise manufacture and fit to precise barrels. This all comes under the first group.
In the second group of factors, it is accepted that a projectile will never leave a barrel with zero yaw or yaw rate. Precision at the target is achieved through reducing the reaction of the projectile to the yaw or yaw rates so that the errors at the target are minimized.
Ideally, you will have both groups of factors working for you, but optimizing one usually comes at the expense of the other. For airguns, it is the minimization of the yaw and yaw rates that is used rather than the projectile design, particularly with pellets which are very poor at dealing with any type of yaw.
All the above assumes of course that the barrel is pointing in the right direction when the projectile leaves it and that it is not flapping about like a flag.
-
Thanks Miles
-
Miles would be the guy to ask about that.... I would like to know as well what is needed to produce consistent fractional MOA groups..... I presume extremely well made bullets is the key, but are there other factors as well?....
Bob
Consistent shooter that knows his / her rifle is the first most important factor. Then comes the barrel and projectile.
And good barrel is what I take before anything else. A good barrel shoots just about any projectile adequate it seem. Where a bad one doesn't shoot any projectile any good it seems.
Marko
-
Yes, it's pretty obvious that you have to start with a good barrel, and one not "waving around like a flag" as Miles said.... My question assumed that, but I remain curious about the relationships between shape and drag, and shape and stability.... There is no question that slugs can "go to sleep" as they travel downrange, and actually produce smaller MOA groups at longer distances.... I know Nick Neilsen has seen that often with his slugs shooting better at 100 yards than at 50....
Bob
-
I know this is about tin vs lead, but what about copper vs lead? Copper is closer in density to lead than tin. I assume the cost is the main reason it isn't used, but might still be viable for hunting.
-
Copper obviously works as a projectile material for firearm bullets. The snag with copper airgun slugs is the high friction that would result from a slug with a cylindrical shank. The snag would start with the force required to imprint the lands in the projectile. Making that engagement shallow to reduce the starting force would probably allow a significant amount of air to blow by the projectile.
Swaging a copper slug results in a cylindrical shank. To take a lesson from powder burner monolithic copper bullets, copper slugs are often lathe turned, with half the bearing area removed in the form of a bunch of shallow "grease grooves".
You could probably turn copper slugs with just a narrow front and rear driving band, that might work from airguns. Still, with airgun barrel land and groove diameters varying so much, the problem would still be that the slugs would rattle in some barrels, and be tight in others. Both lead and tin are soft enough to make them more forgiving with respect to diameter variations (and passing through FX's tight chokes).
Finally, at airgun velocity and energy levels, copper slugs are not going to expand very well. Not unless they have pre-slitted nose petals. Another machining operation, that would chase up the cost even further and doom copper slugs for airguns completely.
For instance; a .326" long copper slug with bearing band OD of .218"; having a nominal radial barrel land to slug shank clearance of 0.004". The slug shown below weighs 15 grains. It could be made with thicker walls, but would be even harder to expand:
-
A more realistic hollow cavity bumps the above copper slug to 17 grains:
-
Good luck getting that out of the barrel. It just wont work, maybe with a bore rider design and plastic driving bands but not with copper.
Marko
-
Yes, Marko; I rather like your idea of adding plastic driving bands. Teflon, perhaps.
I first modeled that copper slug with "foil" driving bands. Then made them .018" wide at the base, so they won't be so easily damaged; yet make very little contact with the barrel.
If you can load such a slug, and the air pressure is high enough to start it moving by a convincing margin, it won't keep having a lot of drag down the barrel. Not close to forces required when engraving the full cylindrical shank length, as is common with a copper jacket centerfire rifle bullet.
There would be an almost 0.1 mm gap between the land tops and the copper projectile shank in my fictitious design. So, less friction than "bore riding".
My real point is that copper complicates airgun projectiles, and solving each new problem raises the cost to the point that such projectiles won't make it from lab to the market.
-
I would be worried about the effects of the slots on the airflow, you may find you have just increased drag and changed the stability. Also, apart from air gunners hating plastic touching the barrel due to bad experiences in the past, you would have to ensure there was no driving band slip. Plastic driving bands are used, but mainly on fin stabilized projectiles, spin stabilized projectiles don't take kindly to reduced spin from slipping driving bands. I suspect they would be horribly expensive.
-
Well, Morris,
Precut or precrimped copper bullets already exist. If we assume that such a projectile would need to be partly machined and partly die formed to close the nose, then those .02" tapering slits could have the petals "line to line".
The objection to plastic bearings on bullets surely comes from ones fired at supersonic velocities? Lower speeds, fired from a reasonably finely finished bore is unlikely to melt or deposit plastic; or am I dreaming?
Why have a cut bullet nose at all? Because at airgun velocities the copper is unlikely to expand. Perhaps that could be addressed by making the meplat larger in diameter and thinning the wall; like this:
-
Segmented bullets. Perhaps only for short range use?
(https://www.cheaperthandirt.com/dw/image/v2/BDCK_PRD/on/demandware.static/-/Sites-ctd-master-catalog/default/dw811fbc45/large/02162.jpg?sw=800&sh=800)
(https://qph.fs.quoracdn.net/main-qimg-159128b11d6d33c8ea952a5b1adfe94a)
(https://aws1.discourse-cdn.com/business6/uploads/cartridgecollectors/original/1X/98d859e04cfd1918ab1707ad9b0cba34ea2c7f6d.jpg)
-
http://www.selwayarmory.com/shop-by-category/bullets/rifle-bullets/45-caliber-457459/shopby/lead_free.html (http://www.selwayarmory.com/shop-by-category/bullets/rifle-bullets/45-caliber-457459/shopby/lead_free.html)
The slugs at the above link inspired me to post the copper question. I guess they are made for a 45/70 cartridge or something.
-
Well, Morris,
Precut or precrimped copper bullets already exist. If we assume that such a projectile would need to be partly machined and partly die formed to close the nose, then those .02" tapering slits could have the petals "line to line".
The objection to plastic bearings on bullets surely comes from ones fired at supersonic velocities? Lower speeds, fired from a reasonably finely finished bore is unlikely to melt or deposit plastic; or am I dreaming?
Why have a cut bullet nose at all? Because at airgun velocities the copper is unlikely to expand. Perhaps that could be addressed by making the meplat larger in diameter and thinning the wall; like this:
I've no doubt that copper bullets with slits etc. in the nose do already exist, it doesn't mean it is a good idea. As you say, at short ranges you can get away with anything if it is a precise fit in the barrel.
On the subject of plastic in the barrel, there are a large number of airgun shooters in the UK who remember the plastic pellets from the 1990's and how difficult it was to get the plastic deposits out of their barrels. Trying to persuade them it is different now is an uphill struggle.
I tested some modern copper bullets when I was working. They were the only bullets tested where we had a radar track of one going completely unstable.
-
What if we took a bore riding copper bullet and gave it two or three coatings with powder coat? That should increase the diameter by some 0.005-6" allowing it to seal on grooves of most barrels.
-
What if we took a bore riding copper bullet and gave it two or three coatings with powder coat? That should increase the diameter by some 0.005-6" allowing it to seal on grooves of most barrels.
Is copper pipe suitable for casting copper bullets? I'm going to try and cast my own .45 ammo this winter. Wouldn't be a big deal to get a .452 (or whatever .005-6 undersize would be for my bore) mold and sizer and cast some undersized slugs. Someone else would have to do the powder coating, although I hope to be able to do that myself in the future. I'm also curious about trying my hand at casting tin, or maybe even a tin/lead mixture that won't fragment. I want to hunt game, but don't want to eat lead contaminated meat, or at least doing my part to not contaminate it further.
-
Shoot them in the head and stop worrying about it.
Marko
-
Shoot them in the head and stop worrying about it.
Marko
It's my choice. That head is still contaminated with lead and then I can't feed it to my dogs, turn it into broth, etc.
-
What if we took a bore riding copper bullet and gave it two or three coatings with powder coat? That should increase the diameter by some 0.005-6" allowing it to seal on grooves of most barrels.
Is copper pipe suitable for casting copper bullets? I'm going to try and cast my own .45 ammo this winter. Wouldn't be a big deal to get a .452 (or whatever .005-6 undersize would be for my bore) mold and sizer and cast some undersized slugs. Someone else would have to do the powder coating, although I hope to be able to do that myself in the future. I'm also curious about trying my hand at casting tin, or maybe even a tin/lead mixture that won't fragment. I want to hunt game, but don't want to eat lead contaminated meat, or at least doing my part to not contaminate it further.
We always get deer sausage and often find bullet particles in them with our teeth. That lead me to believe making deer sausage was a lot easier for the butcher than I thought it was.
-
Is copper pipe suitable for casting copper bullets? I'm going to try and cast my own .45 ammo this winter.
Not, if you are using an aluminum bullet mold:
https://steelforge.com/literature/metal-melting-ranges/ (https://steelforge.com/literature/metal-melting-ranges/)
https://www.metalsupermarkets.com/melting-points-of-metals/ (https://www.metalsupermarkets.com/melting-points-of-metals/)
By the way, powder coating is plastic. Plastic that melts at low temperature and fuses to metal objects. It may be on Miles' list of plastics that foul bores. Then again, there are a number of people on this forum that shoot powder coated bullets and claim less fouling than bare lead.
-
Can you just "paper wrap" a bullet with cyanoacrylate and Teflon tape?
-
Can you just "paper wrap" a bullet with cyanoacrylate and Teflon tape?
You could paper patch it like for some old-timey cartridge gun caliber. The paper is shed after the projectile leaves the muzzle. I am not sure how variations in the shedding process might yank the projectile around...
Gluing on the paper patch may work. Or it may cause partial shedding. Just don't have any uncured CA where it can get on the barrel surface :)
Teflon heatshrink tubing might be an option: https://www.mcmaster.com/75665K862/ (https://www.mcmaster.com/75665K862/)
It is consistent in thickness, but how will it stand up to the journey down the barrel, and into the wild? Trial by fire may be indicated. Size the bullet to accommodate the shrink tubing thickness after heat shrinking. Or select material of the appropriate thickness:
More options: https://www.mcmaster.com/heat-shrink-tubing/material~ptfe-plastic/ (https://www.mcmaster.com/heat-shrink-tubing/material~ptfe-plastic/)
-
Is copper pipe suitable for casting copper bullets? I'm going to try and cast my own .45 ammo this winter.
Not, if you are using an aluminum bullet mold:
https://steelforge.com/literature/metal-melting-ranges/ (https://steelforge.com/literature/metal-melting-ranges/)
https://www.metalsupermarkets.com/melting-points-of-metals/ (https://www.metalsupermarkets.com/melting-points-of-metals/)
By the way, powder coating is plastic. Plastic that melts at low temperature and fuses to metal objects. It may be on Miles' list of plastics that foul bores. Then again, there are a number of people on this forum that shoot powder coated bullets and claim less fouling than bare lead.
There are also people who size up their bullets with powder coating and it seems to work. I haven't tried it but it's getting rather common.
-
I think that plastic bearing surfaces could be addressed in marketing a viable projectile that truly works.
How many types of plastic are there? Just because one leaves a residue in a barrel does not mean all plastics will do that. On the other hand, rough barrels are going to tear off bits of whatever projectile material in contact passes through them. As long as these do not bond to the barrel...
Teflon has the same melting point as lead. Yes, Teflon has lower thermal conductivity and thermal mass than lead. It also generates much lower friction to build heat in the first place.
Teflon O-rings: www.mcmaster.com/o-rings/ultra-chemical-resistant-rigid-ptfe-o-rings-for-tube-fittings-with-straight-thread-connection/ (http://www.mcmaster.com/o-rings/ultra-chemical-resistant-rigid-ptfe-o-rings-for-tube-fittings-with-straight-thread-connection/)
-
I have shot plastic sabot rounds alot and using abs, pla, pom, nylon and polycarbonate. None of them fouled the barrel to any noticeable degree when using silicone lube.
All three calibers actually cleaned the bore with sabots after there was some lead fouling.
Shot with .357 using .223, .457 using .257 and the 20mm using .452 and .50 projectiles.
Too much fussing and talking about how bad lead is, I call it BS from the eco people. We have shot cast and handled over a metric ton of lead and none of us have any measurable exposure that is to any degree unhealthy.
Oh the birds eat it, and so on... lead sinks and is not so easily soluble to water as its too heavy, as for plastic well we have a plastic waste island floating in the ocean. How much does that kill fish and birds?
Speak up on not banning lead and stop thinking about what to do with our hobby.
Marko
-
It may be on Miles' list of plastics that foul bores.
I don't have a list of plastics which cause problems, remember I used plastic in the lightweight slug type designs we experimented with 30 years ago. I am merely saying a lot of air gunners openly say they will not put plastic rounds down their barrels through either having a bad experience in the past or hearing all the stories of fouled barrels. There are certainly plastics where I am sure this would not be a real problem. The main problem, as I was pointing out, though perhaps you did not understand, will be getting over this prejudice against plastics.
-
The main problem, as I was pointing out, though perhaps you did not understand, will be getting over this prejudice against plastics.
Miles, I understood perfectly.
This is all hypothetical, but you get FX to market the plastic coated slugs, and Dubber and his buds to shoot them; and Bob's your uncle :). https://en.wikipedia.org/wiki/Bob%27s_your_uncle
If magic slugs cost too much, no one will buy them. If they work and don't cost too much people will be eager to try them. If they like the slugs, they will buy more.
-
I have shot plastic sabot rounds alot and using abs, pla, pom, nylon and polycarbonate. None of them fouled the barrel to any noticeable degree when using silicone lube.
All three calibers actually cleaned the bore with sabots after there was some lead fouling.
Shot with .357 using .223, .457 using .257 and the 20mm using .452 and .50 projectiles.
Too much fussing and talking about how bad lead is, I call it BS from the eco people. We have shot cast and handled over a metric ton of lead and none of us have any measurable exposure that is to any degree unhealthy.
Oh the birds eat it, and so on... lead sinks and is not so easily soluble to water as its too heavy, as for plastic well we have a plastic waste island floating in the ocean. How much does that kill fish and birds?
Speak up on not banning lead and stop thinking about what to do with our hobby.
Marko
Without taking this thread into the weeds with science and evidence, lets just say you are mistaken. I won't use plastic either due to the toxic effects. There are plenty of stories of guys casting ammo getting tons of lead poisoning, you just aren't looking. Today we understand the toxic properties of lead and problems arising from casting are less common, than they used to be. Millions of people suffered from the effects of TEL which has only been taken off public roads worldwide this year. Furthermore the NIH has determined that lead dust can and will be absorbed by skin in the presence of sweat and water. Just because you personally don't experience something doesn't mean it isn't a problem for other people.
This is the last I'm going to speak on the dangers of lead in this topic, but keep in mind this THREAD is about lead projectile alternatives. If you don't care about not using lead, then leave. Nobody is asking for your opinion about lead ammo, your opinion is well documented, and there really isn't anything else left for you to add.
-
Miles,
While I participate in the sideline discussions in how to make projectiles from other metals, the bottom line is that lead is hard to beat, with tin as a reasonable non-toxic second.
Bismuth is another non-toxic substitute that perhaps could be considered. I think bismuth is denser than tin, but has other shortcomings. It is used for shotgun pellets to reduce lead contamination of duck and goose habitats.
It looks like 10 lbs of .18" diameter bismuth shot pellets is expensive, at $200. Turning that into slugs or pellets would probably double the cost:
https://www.rotometals.com/bismuth-shot-bb-18-4-60mm-alloy-for-reloading-shells-10-made-in-usa/ (https://www.rotometals.com/bismuth-shot-bb-18-4-60mm-alloy-for-reloading-shells-10-made-in-usa/)
Here, bismuth pellets are fired from an airgun:
https://www.youtube.com/watch?v=N7N-FZBKZ0g (https://www.youtube.com/watch?v=N7N-FZBKZ0g)
I get the impression that pure bismuth is brittle.
Perhaps a tin bismuth alloy could be considered:
https://www.youtube.com/watch?v=s1CNGMElWfA (https://www.youtube.com/watch?v=s1CNGMElWfA)
-
Miles,
While I participate in the sideline discussions in how to make projectiles from other metals, the bottom line is that lead is hard to beat, with tin as a reasonable non-toxic second.
Bismuth is another non-toxic substitute that perhaps could be considered. I think bismuth is denser than tin, but has other shortcomings. It is used for shotgun pellets to reduce lead contamination of duck and goose habitats.
It looks like 10 lbs of .18" diameter bismuth shot pellets is expensive, at $200. Turning that into slugs or pellets would probably double the cost:
https://www.rotometals.com/bismuth-shot-bb-18-4-60mm-alloy-for-reloading-shells-10-made-in-usa/ (https://www.rotometals.com/bismuth-shot-bb-18-4-60mm-alloy-for-reloading-shells-10-made-in-usa/)
Here, bismuth pellets are fired from an airgun:
https://www.youtube.com/watch?v=N7N-FZBKZ0g (https://www.youtube.com/watch?v=N7N-FZBKZ0g)
I get the impression that pure bismuth is brittle.
Perhaps a tin bismuth alloy could be considered:
https://www.youtube.com/watch?v=s1CNGMElWfA (https://www.youtube.com/watch?v=s1CNGMElWfA)
When I get casting tools I would be willing to try.
-
Miles,
While I participate in the sideline discussions in how to make projectiles from other metals, the bottom line is that lead is hard to beat, with tin as a reasonable non-toxic second.
I am not advocating any alternative to lead. All I am doing is pointing out the problems from the ballistic viewpoint. There are problems with all the alternatives, that is why we use lead. But there are very real possibilities that lead will not be available in the future, so it only makes sense that the alternatives are examined and the problems considered.
-
I believe the issue airgunners may have with both lead and plastics are both rooted in their association with firearms. Hot gasses (fire) and primers (lead inhalation?).
I had a dedicated slug shotgun that had been shot so much with (wad) plastic slugs the barrel wouldn't come clean. That was a plastic issue due to either fire, speed or pressure of a PB. It was shot a lot before I got it.
If you read up on lead bullets used in firearms there is a limit to how fast you can push them before you get leading.
-
If you read up on lead bullets used in firearms there is a limit to how fast you can push them before you get leading.
You will get arguments about what that velocity limit is, but it is well over the speed of sound; when grease lubed bullets are used. Lead bullets are less common for rifle calibers because of this velocity limit. What will lead a handgun barrel badly is shooting undersized bullets, because that allows a lot of hot gas to blow by the bullet. Thus melting the bearing surface of the bullet and plating the bore with lead.
Airgun slugs are usually sized no larger than groove diameter, to reduce friction. In .177 and .22 calibers, slugs used are often 0.001" smaller than groove diameter. There is no risk of hot gas blowby melting the lead surface due to less than a perfect air seal. Pellet skirts start larger than groove diameter, but the force required to make them conform to the barrel is low, and subsequent skirt friction down the barrel is not significant.
With firearms, grease lubed bullets that contain tin and antimony to harden them, foul less than pure lead ones. With airguns, pure lead projectiles lead foul less than ones containing significant percentages of antimony. So, there is some commonality, but the leading problem and mechanism are not identical for airguns.
Once you have significant lead, plastic or copper fouling plated to the bore, it tends to increase friction with subsequent rounds. That heats up and tears of more material, so the condition can run away. This tends to open groups and raise pressures (in firearms).
The regime is preferred where each projectile scrubs out the little fouling the previous projectile laid down. This allows many shots without cleaning becoming imperative. There are many factors in establishing such a stable system, with bore finish being one of them. Using the "right lube" can also prevent fouling from adhering strongly to the barrel. Exposed bullet lube has to be managed, to prevent it from picking up and carrying abrasive down the barrel...
When it comes to plastic fouling of shotgun barrels, I wonder what cleaning regimen is used on those $2000 Browning Citori shotguns they rent out at skeet ranges? Or, are they smart enough to use ammo that has shot cups made from non or less fouling materials?
-
What if we took a bore riding copper bullet and gave it two or three coatings with powder coat? That should increase the diameter by some 0.005-6" allowing it to seal on grooves of most barrels.
Is copper pipe suitable for casting copper bullets? I'm going to try and cast my own .45 ammo this winter. Wouldn't be a big deal to get a .452 (or whatever .005-6 undersize would be for my bore) mold and sizer and cast some undersized slugs. Someone else would have to do the powder coating, although I hope to be able to do that myself in the future. I'm also curious about trying my hand at casting tin, or maybe even a tin/lead mixture that won't fragment. I want to hunt game, but don't want to eat lead contaminated meat, or at least doing my part to not contaminate it further.
We always get deer sausage and often find bullet particles in them with our teeth. That lead me to believe making deer sausage was a lot easier for the butcher than I thought it was.
Case and point. Just eating some homemade chilli with deer meat and chomped on what I thought was a small bone. Copper-clad lead bullet fragment. Odd thing, all the deer we've got in the freezer are from either bow/arrows or pure lead airgun bullets. I always wondered how Boris the butcher turned around deer so fast.
(https://www.gatewaytoairguns.org/GTA/MGalleryItem.php?id=8211)
-
OT but, you dont butcher your own kills?
There is no velocity limit on where leading will start to happen, it's going to be more related to the surface finish than anything else. Rough bores gather more lead no matter what the velocity is.
Marko
-
OT but, you dont butcher your own kills?
There is no velocity limit on where leading will start to happen, it's going to be more related to the surface finish than anything else. Rough bores gather more lead no matter what the velocity is.
Marko
Our family used to get together after opening weekend for butchering (good times unless you are from PETA - wrong place/time) but they aren't around and it gets busy during the deer season.
I probably need to clean a couple airguns. I used to love cleaning a rifle but haven't done much on airguns except the D34.