A guy that is member of a shooting team e-mailed me asking how to solve a problem they are having with bullet tipping up to 10-degrees at a 300 meter target. They are shooting competition with 6 mm BR using 105-grain VLD (very low drag) bullets. All the bullets from different bullet makers are doing the same thing. But they do report good groups.
What I said is not required for everyone in every situation, come on now. But is not this the reason we swag bullets to get the best out of our firearms.
The reasons for using other materials then lead is to make a bullet that is balanced just right so it follows point first the curvature of its trajectory to maintain the lease amount of drag forces and too change the bullets mass density for a given length or to change the bullet’s length without changing its weight. This has the effect of changing the amount of spin that a bullet needs to properly stabilize in flight. If we can get a good bullet weight for bullet length, the bullets sectional density will increase there by increasing the bullet’s Ballistic Coefficient at the same time matching the bullet with the firearm’s rifle twist rate or even allowing for a barrel with a slower twist rate than would be normally possible. When a bullet can stabilize with the slowest twist rate possible it means that any errors in the bullet, firearm, ammunition, atmospheric conditions are reduced, or unnoticeable, to the bare minimum. This is done because different materials have different densities and it is this difference that we use to change the characteristics of a swaged bullet.
Does this mean that we have to do it to get good results? NO, it might not be economically worth it or worth our time and effort. But from a theoretical or even an experimental viewpoint don’t rule it out. This is not for the dull people out there that just settles for; I’m satisfied with what I have and there is nothing wrong with that, I do it too at times, that’s were not economically worth it or worth my time and effort comes into play.
If you are still unsure of how different density of materials can change the of rifle twist read my page on “Rifling & Bullet Spin” at my web site and play with the numbers. But realize that there is a domino effect when you do this too.
Just for your information here is my e-mail, in part, that I sent back to that guy.
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The problem: simply put, your bullet length to rifle twist rate ratio is off.
1. The twist rate is too slow for the bullet length; your group is trying to shoot, to stabilize.
2. The bullets, your group is trying to shoot, are too long for the rifle twist rate to stabilize.
Now there are a number of solutions for this and one of them your group has already tried and that is to use a shorter bullet, but that did not have the best solution because the bullet’s weight went down due to it’s shorter length thus causing the sectional density dropped there by lowering the Ballistic Coefficient of the bullet. This causes two things to happen:
1. The lighter weight of the bullet is more susceptible to the effects of wind drift.
2. The lower sectional density of the bullet has, by nature, a lower Ballistic Coefficient and this will make the bullet more susceptible to the drag forces of air and the bullet will lose velocity faster. This will:
· Cause the bullet to have a longer lag-time, which means the bullet will be in the crosswind effect longer for greater drift.
You can see the domino effect caused by changing one aspect, the length. But in reality you were changing several aspects all at once, I was just pointing out one of them.
Now lets look at solutions that will keep your current rifling twist rate the same. By changing the bullet in regards to it’s length, sectional density, and internal balance along the longitudinal axis. This is where a custom bullet swagger comes into play quite nicely. As a side note, swaging is the process of making metals flow at room temperatures by the application of high pressures.
1. One of the easiest ways is to change your bullets point of balance along the longitudinal axis while keeping the bullet’s mass density concentric.
· This would be to introduce a lesser or greater density material as part of the lead core to change the balance point of the bullet. If the bullet is too tail heavy, as in your present bullets, it will require more spin to stabilize the bullet and the effects of forces acting on and within the bullet are greatly magnified with increasing spin. If the bullet is too nose heavy the bullet will require less spin to be stable. As your barrels are a set twist rate this might cause the nose heavy bullet to be over stabilized which would not allow the nose of the bullet to follow the ballistic curve of trajectory, but to remain in the angle of departure and then as the trajectory decreases from the angle of departure more of the side of the bullet is presented to the air increasing the drag forces and causing the bullet to fall short of it’s target and to be deflected off course by the gyroscopic action of precession. The point of balance that is the best for a bullet is to place it just slightly aft of it’s center.
2. If the bullet is still not being stabilized by your 1:8 twist the next thing to do is to increase the bullets mass without increasing it’s length. This can be done by replacing more of the bullet’s lead core with a denser material while keeping the same point of balance, previously been mentioned. By increasing a bullet’s density this will do several things at once. It will increase it’s sectional density there by increasing it’s Ballistic Coefficient while decreasing it’s wind drift and the amount of spin required to stabilize a given bullet length. With a greater density bullet this means the velocity will have to be less but some of the loss of velocity will be made up with a greater velocity do to less twist rate. What I mean is for an example: if the higher bullet weight do to a greater density of core material you might loose 250 meters per second but you can increase the velocity by 50 meters per second because there is less of a twist rate, so your net loss in velocity is only 200 meters per second vice 250 meters per second. But for longer ranges the increase of Ballistic Coefficient will more than make up for the loss of a little velocity.
· If we have a 6 mm, .243 inch, bullet that is 100 grains that is 1.200 inches in length, according to the formula:
· (Bullet diameter, in inches, squared times 150) divided by bullet length, in inches, equals twist rate in inches.
· (.243^2 * 150) / 1.2 = 7.38 twist rate or a 1:7 49/128th or just over 1:7 3/8 inches.
· This is with a bullet that has a lead core that has a mass density of 11.35. If we were to change this from a lead core to a powder Tungsten core with a mass density of almost 19.3, that is an increase of 7.95 times greater. For the same length of bullet the weight would be not 100 grains but about 170 grains. But if you want the same weight bullet out of powdered tungsten the length would be about 2 inches long. But in the case of the shorter but heavier bullet the twist rate would decrease from 1:7.38 to 1:9.82. This is but one example; there are lots of different powdered materials to use. By using powdered materials it is easier to mix and swag and there is no chance of it being classified as an armor-piercing bullet. There is powdered lead, copper, iron, silver, tungsten, and others. Since the materials are in a copper jacket there is nothing to hurt the bore of the firearm.
The new thing is to change the twist rate of you barrels. I would think that this is the less desirable option. By doing this your incurring a large cost of another barrel. The twist rate would be upwards of 1:7, not the best. Remember that the forces are greater with greater twist rates.
In conclusion; I would suggest getting yourselves a custom bullet swagger that is willing to work with your group in varying the different elements of the bullet’s characteristics to match the bullet to your firearms and shooting conditions. This approach is going to take some time, so who ever you get, be patient and I think you’ll find that the rewords will be well worth the effort.
I hope this was helpful?
May all your groups be one holler’s.
Donna
