zan boat tail slugs
- Thread starter oldhermit
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I was just thinking if boat tail slugs have better BC than hollow or flat base slugs. I wait for the experts to reply.
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A correctly designed boat tail will reduce the drag and thus increase the BC. At the same time, it also makes the slug more aerodynamically unstable, so an increase in twist rate may be needed for optimum performance. If the boat tail is just added to an existing slug it will make it longer and increase the mass which will also increase the BC but not through anything aerodynamic.
If the boat tail is not correctly designed, it will not reduce the drag as the airflow will not be able to follow the boat tail contours. There may in addition be variations in the way the air sees a wrongly designed boat tail, which can give additional stability problems.
Designing a boat tail is not just a case of putting a truncated cone on the back of a slug and getting an increase in BC. Many of the boat tail slug designs I have seen appear to have much too long a boat tail with too big an angle on the sides, and thus are probably not doing anything very positive. Some of them appear to have just about every "don't do that" that you can think of for boat tail design, but on the positive side, a bit of good marketing can always replace a lot of good science and is much cheaper.
If the boat tail is not correctly designed, it will not reduce the drag as the airflow will not be able to follow the boat tail contours. There may in addition be variations in the way the air sees a wrongly designed boat tail, which can give additional stability problems.
Designing a boat tail is not just a case of putting a truncated cone on the back of a slug and getting an increase in BC. Many of the boat tail slug designs I have seen appear to have much too long a boat tail with too big an angle on the sides, and thus are probably not doing anything very positive. Some of them appear to have just about every "don't do that" that you can think of for boat tail design, but on the positive side, a bit of good marketing can always replace a lot of good science and is much cheaper.
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Ballisticboy,
For the love of all that is Holy, please design us a pellet.
. I'm sure it would also take more air because you don't have a flaring effect from a rear skirt.Smitty
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Let's not mince words... Do you think the Altaros slugs are a less than optimal bt design? Or these new Zans?
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@Ballisticboy With that said, I tend to see rebates boattail slugs. Is this a better design for Airgun slugs than a standard boattail projectile? I like Griffin Airgun Ammo boattails, but I am clueless as to whether the design is sound. I’m usually not a long-range shooter so I’m not the best person to judge long-range performance. I’m asking because as I shoot from further out, I’d like to know what to expect realistically from this slug design.
@oldhermit I have no idea, but let’s ask @ZAN for info concerning their new boattail slug offerings.
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Are you trying to get me sued?
I have not seen anything on the Zan slugs or any actual pictures of the rounds as made, so I cannot comment on those. As for the Altaros slugs, all I have seen are the pictures in their adverts and on their website. To me, the boat tail looks longer than I personally would have used. About half a calibre is as long as you want to go, anything much longer than that is just for bragging. I don't know about the angle of the sides. The maximum angle that can be used is only about 5-6 degrees for smaller calibre slugs. The maximum angle will vary depending on the size and muzzle velocity of the slugs but should not be more than about 8-9 degrees.
The rebate on slugs and bullets is there to help as the slug leaves the barrel. Its purpose is to reduce the effects of high pressure gas coming out of the barrel and overtaking the slug/bullet. It reduces initial yawing rates and improves group sizes at shorter ranges.
Below is an example of one of Bob Sterne's BBT slugs where he modified the boat tail to match my suggestions with apparently good results.
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Lol of course not. Thank you for the data behind your evaluation. I might take some measurements later out of curiosity.
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Altaros must be doing something right, since their Altaros ATP Smooth .25 caliber 49.5 grain slugs have a measured BC of 0.21 G1 and 0.110 G7 at 890 fps. This is almost twice the BC of other .25 caliber "standard" slugs.
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Mine are perfectly stable out to 300 yards. I haven't shot further than that. They were stable enough to win the Ashland Oregon Long Range Challenge last year 120 to 260 yards with a perfect score...
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The two BC values above don't actually give the same Cd value so one of them is not accurate, probably the G1 value, as to use G1 for a bullet of this shape is ridiculous. The two values of Cd are 0.137 from the G1 BC and 0.128 from the G7 value. For comparison, the lightweight .22 14.5 grain slug in my avatar had a measured best Cd of .132, I was never interested in BCs at that time when we fired them in1990, and I know the boat tail on that was not correct.
So yes the Altaros does well, but it could possibly do slightly better with a smaller boat tail.
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Thanks. I use the 0.110 G7 BC at 888 fps and my trajectory validation is spot on from 20 to 300 yards. Altaros advertises 0.21 G1 BC on their slug packages but via e-mail recommend using the G7 profile.
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I'd be interested to see how your trajectory works out with the SLG1 profile from Mero. Mero will do a basic BC conversion for you when you switch profiles.
Also curious how the Altaros might fly if you had the equipment to shave off, say, 30% of the boattail, and bring it back to a recommended size. I have not gone into my stock to measure anything, but memory suggests the angle is probably OK.
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They fly so well I wouldn’t mess with them. If something works, and works as good or better than anything else on the market, my instinct is to leave it alone.
I’m curious why my trajectory would be any different? I’ve shot every 25 yards from 25 to 300 yards and it’s spot on at all yardages.
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The Altaros boat tails also key into the FX probes very nicely, providing smooth and axial loading. Therefore the design may be a compromise between optimal aerodynamics and ease of use in the FX rifles.
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I mean, I'm curious how closely the SLG1 profile matches up to G7 for you. SLG1 is supposed to be tailored to this style of slug, round nose with BT (if I'm not mistaken), it's just experimental. So since you have accurate dope out far, which a lot of people probably don't, might be a good comparison.
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