Author Topic: Bi-metal slugs  (Read 1090 times)

Shorty

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Bi-metal slugs
« on: January 13, 2017, 01:14:42 PM »
Would there be any value to a bi-metal slug to reduce the weight while keeping that bullet shape to keep a good or better BC than a pellet?

 I kind of figure that slugs or bullets are the wave of the future but most bullets need some length which adds weight and reduces the speed from BB guns to achieve the correct RPM to stabilize in our "stocker" barrels.

Let's just say if one was able to make an annealed aluminum wire (8176Al or 1350Al) and throw it in a lead tube, then draw it (making a bi-metal), can a person with swagging equipment spit out a bullet that is 30% lighter but have the length for stability along with our BB guns delivering the FPS for the RPM for stabilization ?

Just a pondering question since I have the capabilities of making the raw material (not the swagging stuff).


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Alan

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Re: Bi-metal slugs
« Reply #1 on: January 13, 2017, 03:01:16 PM »
Well, that is not exactly how it works. Weight does matter, as does length. However, the real data point is BC (ballistic coefficient). And, it is sort of difficult to beat lead for weight, although bismuth and tungsten come close. Aluminum? Nada!

By the way, slugs (versus pellets) will not take over the airgun ammo market anytime soon if ever. Slugs are spin stabilized, and pellets are both spin and drag stabilized. Most of todays pellet guns will not shoot slugs, albeit some are designed to do just that.
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rsterne

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Re: Bi-metal slugs
« Reply #2 on: January 13, 2017, 03:23:17 PM »
The primary component in the BC is the Sectional Density or SD, which in any given caliber means weight.... the heavier it is, the better the BC.... The other component in the BC is the "Form Factor", which is related to the drag of the particular shape involved.... They are all related by the formula....

BC = SD / FF

In a given caliber, if you keep the weight constant, you have a fixed SD, so the only way to a better BC is by lowering the FF.... In a nutshell, this means longer bullets, but if the weight is a constant, you then need a lower density.... Yes, you could make a Bi-Metal bullet, if you could control all the variables to make sure the core remained consistent and concentric with the OD.... but an easier way to experiment is just to cast some bullets up in pure Tin.... It has a density of 7.31, compared to lead at 11.34, so it's less than 2/3rd of the weight.... It isn't a lot harder than lead, and has a low melting point, so you can cast it in conventional bullet moulds.... If you used the mould for my 51 gr. BBT in .25 cal, you could end up with a bullet that only weighed 33 gr. instead of 51, but looked the same, and had the same FF.... Unfortunately, the BC would still only be 65% of the lead version.... so it would drop from about 0.11 down to about 0.07.... A 34 gr. JSB Heavy is about 0.053 for comparision....

As far as stability is concerned, the less dense the bullet, the faster you have to spin it.... Whereas my 51 gr. BBT is designed for a 14" twist, if you made it out of tin, you would have to use an 11" twist barrel to get the same stability.... So, yes, what you are suggesting is possible.... but you will need a MUCH faster twist rate for it to be accurate.... Tin is also much more expensive than lead, of course....

Bob
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oneshot61

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Re: Bi-metal slugs
« Reply #3 on: January 19, 2017, 02:31:21 PM »
Ron from Higharchunter made some .357 97? Grain for me to test. For my shooting they were accurate at 100 yards. You may want to talk with him about it as far as the casting particulars.
« Last Edit: January 19, 2017, 02:33:44 PM by oneshot61 »

Shorty

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Re: Bi-metal slugs
« Reply #4 on: January 19, 2017, 05:50:02 PM »
Thanks for the link oneshot61. Never heard of that company.
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