Zinc bullets for magnum and rifle loads Part II

[davidh0302]

I recently tested my zinc 223 Rem loads.

As I posted above I sized the bullets to .224.

I shot them out of a HK SL6 which has about a 11" twist rate and polygonal rifling.

Accuracy was horrible, shot at 50m dispersion was about 30 cm. Some bullets even tumbling and hitting sideways.

I don't have the possibility to chrony my loads at the moment, but the balistic software calculates a muzzle velocity of about 1090 m/s.

To test wether the polygonal rifling has something to do with this stabilizing problem, I shot the same loads out of my recently acquired swedish Mauser Frankenrifle with a enormous match barrel chambered in 223 Rem. Accuracy was marginally better 20-25cm and no keyholing.

But still this is nowhere near acceptable accuracy.

I'm thinking about sizing to .225 or bigger and try again.

What do you guys think?

Thanks in advance for your help.

David

PS: here's the link to my original ZINC bullets post
http://castboolits.gunloads.com/showthread.php?399005-Cast-ZINC-bullets-for-magnum-and-rifle-loads&highlight=Zinc

[SHORT SHELL]

I had put my results on your first thread so not to repeat my self all I can report is zinc is not good for accuracy. Stick with lead until it is outlawed world wide then something else will be found but not zinc. Copper powder in an epoxy is a promising solution for home moulding.

[Winger Ed.]

I'd try getting the speed up into the mid 2,000s.

Some guys are saying Zinc boolits will get to almost jacketed speeds.
If you use jacketed data, since they are lighter, they'll come out faster.

You might try the minimum charge weight for 50 grain FMJ.

To help eliminate the Zinc boolit being your accuracy problem, try a light weight jacketed one with the same charge, at the same range.

[davidh0302]

I had put my results on your first thread so not to repeat my self all I can report is zinc is not good for accuracy. Stick with lead until it is outlawed world wide then something else will be found but not zinc. Copper powder in an epoxy is a promising solution for home moulding.As I said they work perfectly fine in my 308 Winchester at over 900 m/s. 2 cm at 100 m.
The 224 and 309 diameter bullets are even completely the same design, the 224 is just shrunken in all dimensions.
Velocities achievable with lead bullets even coated (I use them for all my pistols and revolvers, for my 44 Mag Desert Eagle I use zinc), are not acceptable for me, 2000 fps is not an acceptable velocity for 30 caliber and the like, maybe for heavy hitters in calibers above 40 cal like 45/70 and 444 Marlin. I'll try Coated cast lead bullets in my 35 Rem soon.
My goal is to cast bullets capebale of jacketed velocities. No less.
It worked in 308, so I'll figure it out for other calibers. Or at least find out why exactly it isn't working in 223 (yet).


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[davidh0302]

I'd try getting the speed up into the mid 2,000s.

Some guys are saying Zinc boolits will get to almost jacketed speeds.
If you use jacketed data, since they are lighter, they'll come out faster.

You might try the minimum charge weight for 50 grain FMJ.

To help eliminate the Zinc boolit being your accuracy problem, try a light weight jacketed one with the same charge, at the same range.I tried PPU 45 gr jacketed bullets with the same load, they worked just fine.
It seems pure zinc is still to soft for the bullet (3 driving bands) with full loads.
I tried the zinc 45 gr zinc bullets with three loads all Lovex D073.5: 27gr, 22gr and 17gr, they all showed similarly horrible accuracy.
My guess is, I have to try a bigger diameter, at least. 226, my mold casts at. 227 so I just have to size to .226 diameter to try that.
Next step would be to bore out the driving bands in the mold, to cast a slick sided bullet.

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[rintinglen]

1090 M/sec is 3,576 fps!
I suspect that if this is the case, you are shooting the bullet too fast for the strength of the zinc and it is deforming asymmetrically. There were some pretty interesting (and heated) discussions of the effect of RPM on lead cast bullet high velocity accuracy. Larry Gibson and a former member had some detailed
and extensive arguments that frankly, were a bit beyond my comprehension.

But to summarize as best as I can remember, slower twist barrels allowed for better accuracy. Rotational speeds in excess of 140,000 RPM were associated with severe degradation of accuracy, presumably due to rotational distortion. Since the RPM was a function of twist and velocity, slowing the one allowed the other to increase, while still remaining below the threshold of 140,000 RPM. Now these considerations were for "hard" lead boolits, and your Zinc castings are harder yet, but I surmise that there is some similar threshold that is affecting your results. You might want to decrease your velocity to 750-800 M/s and see how accuracy is affected. If I did the math right, your "zoolits" are spinning at 234,000 + RPM.

[davidh0302]

1090 M/sec is 3,576 fps!
I suspect that if this is the case, you are shooting the bullet too fast for the strength of the zinc and it is deforming asymmetrically. There were some pretty interesting (and heated) discussions of the effect of RPM on lead cast bullet high velocity accuracy. Larry Gibson and a former member had some detailed
and extensive arguments that frankly, were a bit beyond my comprehension.

But to summarize as best as I can remember, slower twist barrels allowed for better accuracy. Rotational speeds in excess of 140,000 RPM were associated with severe degradation of accuracy, presumably due to rotational distortion. Since the RPM was a function of twist and velocity, slowing the one allowed the other to increase, while still remaining below the threshold of 140,000 RPM. Now these considerations were for "hard" lead boolits, and your Zinc castings are harder yet, but I surmise that there is some similar threshold that is affecting your results. You might want to decrease your velocity to 750-800 M/s and see how accuracy is affected. If I did the math right, your "zoolits" are spinning at 234,000 + RPM.The problem I am trying to solve is: Why do my .309 zinc bullets going at 920 m/s work and my .224 zinc bullets going at 1090 m/s do not.
As a stated in my original post my very fast 308 loads do work perfectly.

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[charlie b]

Have you been able to recover any of the bullets? I wonder if the rifling is skidding at that velocity and diameter.

[davidh0302]

Have you been able to recover any of the bullets? I wonder if the rifling is skidding at that velocity and diameter.No, but they make perfectly round holes, at least when shot trough the conventional match barrel.

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