The ZLUG Thread

[Hogtamer]

OK, we've talked about it and after weighing the pros and cons I'm going to try to produce a full bore ZINC slug load for a 3" rifled 12 guage. I just ordered this mold from Accurate Molds.
http://www.accuratemolds.com/bullet_...=73-860B-D.png

From what I can read the Zamak 3 alloy looks like the best choice, so this will be coming soon.
http://www.rotometals.com/product-p/zamak-3-ingots.htm

If I can cast these it should yield a slug that weighs 1.31 oz. There's a 3 week turnaround on the mold. In the mean time I will aqcuire a new clean pot and ladle to insure no contamination. Until I actually begin casting trials, comments are welcome, especially about load recommendations and wad column composition. My powder choices are Steel, Longshot and 800-X. Wish me luck and let's have at it!

[OBCoal]

Good luck and hope it works out for you. Nice looking slug mold.

[longbow]

I guess my only comment is that the bearing bands look pretty beefy for a slug as hard as zinc. It might take some pressure to engrave that boolit.

Not sure how one would check that other than to use a barrel push through to determine just how much force is required to engrave then use that to determine pressure.

I don't think it would phase me in a center fire rifle but I have visions of a snake swallowing a gopher when I think of a hard slug being pushed through a thin walled shotgun barrel... or are you using an bull barrel?

Regardless, I would use the slowest shotgun powder you have to minimize pressure spike.

If the slug shrinks more than lead then engraving may be fairly shallow so mitigating the hardness issue some. Hard to say without testing. Maybe someone has already tried and can advise.

I think I would be inclined to use felt or fiber wad under the slug to raise it up to crimp height and for a bit of cushion effect, and a good plastic gas seal over the powder.

Just my thoughts.

Longbow

[cpileri]

I'm interested.

[Red River Rick]

Cutting the Sprue on a zinc bullet may prove a bit troublesome.

RRR

[Hogtamer]

Thinking may have to enlarge sprue hole a bit and quick pore with ladel at ~ 800*. Would the Zamak 3 (about 4% aluminum) be a better choice tha pure zinc? If I understand the bit of aluminum would help fillout. Any shared experience would be welcome.
LB, the fit to bore is a bit of a **** shoot until I actually get the mold and cast some I think. The snake swallowing the gopher is a disturbing image something I plan on avoiding. Depending on actual size of mold (+ or - 002) and amount of shrinkage I really don't know what to expect. What would be acceptable amount of pressure to get slug down bore if it is oversize considering hardness of alloy?

[bikerbeans]

HT,

I hope ur mold works with zinc, because a 2 oz lead 12ga slug will be a handful at normal slug velocity. Good luck and keep us posted.

BB

[longbow]

Yeah, Red River Rick brings up a good point too about cutting the sprue. That may well be troublesome. I would not go enlarging the sprue hole at least until you do some casting.

I will say that one of the ZAMAK alloys is probably better than pure zinc... that or a die casting alloy. Die casting is done under pressure but the zinc also has to flow well so a die casting alloy might be the best overall.

You may also have to pre-heat that mould quite a bit before casting. Another reason to go with iron.

Sizing will also be an issue if the slug is big. Not sure how you handle that. Seems to me turbo had some comments about that in a post. I would figure a knurled or tumble lube grooved slug might allow zinc to be sized easier than with beefy (like skookum) driving bands. Now a hammer sizing die might just work okay. Turn the correct sizing die diameter, make a close fitting punch and use an "appropriate" sized persuader (hammer) to drive the slug through. Likely much easier than trying in a press. Hmmm... unless you have an arbor press that is.

You may well not need or want a full groove diameter slug and a plastic gas seal behind will take care of gas so no need anyway. I think engraving effort will be what you want to optimize and with zinc as hard as it is you may not need a lot of engraving depth.

All speculation on my part though.

I do work for a lead/zinc smelter so I will see if I can get any info on best zinc alloy for casting. Not sure I will get anything as the plant just mixes alloys to suit clients orders and we do not do any casting except slabs and jumbos... no small parts.

This will be interesting. I am glad you have taken the jump and are giving it a try.

Longbow

[bikerbeans]

LB,

If it would take a hammer to "push" a zinc slug through a size die, what would it take to remove a zinc squib from halfway down the bore?

BB

[longbow]

Well, good question. I have to think that once engraved if wouldn't be too bad. I think the initial engraving might be the issue. But again, speculation on my part.

Longbow

[Hogtamer]

Disappointment....Got an email and a refund from Tom at Accurate mold. He's very thorough and when I told him to use a 5% thermal shrinkage rate from zinc alloy he calculated that to get a .729 slug the mold would have to be .766, too big for the blocks he uses. While that speaks well for his attention to detail it leaves me with no alternative that I have come up with yet. The 5% number is a bit arbitrary as metallurigcal sites I visited gave shrinkage rates from 3.5% to 6.5%, so I used a mid-range and hoped to get lucky. What I am considering now is casting some minies from a lyman mold I have that casts oversize in lead, using the Zamak 3 alloy and trying to determine an actual shrinkage rate to work with. From that I can perhaps come up with a more precise guesstimate that would allow me to buy a slug mold that would cast .600 in zinc to fit some steel shot wads I have to create a sabot slug. Nothing seems easy! Anyone with a better idea? Seems that a member here who has actual experience with zinc (turbo 1889) pulled his threads and no longer participates in the forum. Does anyone have email contact info for him that he might communicate privately? Failing that, any suggestions about where to go with this?

[cpileri]

Looks like you are stuck w a wad-slug combo; which does eliminate some of the problems that have been brought up; i'd say.

Still interested!

C-

[Red River Rick]

I've machined hundreds of moulds over the past 25 years for a customer of mine that does zinc injection moulding. I've used 0.06% (0.006" per inch) as a shrinkage value and never had any problems.

BTW, if you add 0.06% to 0.729 you get a diameter of 0.7334.

RRR

[longbow]

Hey Hogtamer... take a look here:

http://www.eazall.com/diecastalloys.aspx#Alloy Description

This says ZAMAK #3 shrinks 0.007"/inch.

I should probably know more about this since I work for a lead & zinc smelter but we only produce raw zinc and lead ingots cast in open face moulds so shrinkage is not something anyone ever worries about or measures. Also, being open face moulds there is lots of molten zinc to replace initial shrinkage.

Anyway, I have to say that 0.007"/inch seems more realistic than 5% and it is in line with what Red River Rick says too.

Here is another link with about the same shrinkage rates:

http://www.brockmetal.com/wp-content...OMP-LOWRES.pdf

I have to think that 5% is incorrect.

At worst you could cast into an oversize hole in sand or plaster then machine slugs from that core. It would be a bit of work but you would get exactly what you want for testing. Afterwards a mould could be made to suit.

Longbow

[Cap'n Morgan]

The shrinkage rate of 5% is not unusual. I believe it is about the same for lead. The thing to remember is that the sprue (or deadhead) makes up for the shrinking as the cast solidifies. What we boolit casters normally think of as shrinkage is the amount of shrinking from a hot, but solid boolit, to a room temperature boolit. This can be calculated when you know the thermal expansion for the material used and will typically be between 0.5 to 0.8% for lead, depending on the alloy and mold temperature (and mold material):

http://www.engineeringtoolbox.com/li...on-d_1379.html

[longbow]

Yes, Cap'n Morgan brings up a good point. Lead poured in open moulds shrinks far more than we experience in boolit moulds. Same should apply to zinc.

The figures in the links I gave are for shrinkage in moulds with liquid zinc allowed to flow to replace shrinkage as required similar to what we get in boolit moulds.

Longbow

[Hogtamer]

Ok, so .007 or 7/1000 is the shrinkage to expect in a slug sized boolit mold and 5% or 5/100 is shrinkage in open pour (I'm visualizing pouring into a can)? 7/1000 would be no problem for Tom @ accurate. LB and others, take a look at this page and see what slug you think would cause the fewest potential problems....nothing over 860 grns though...
http://www.accuratemolds.com/bullet_...=73-770S-D.png

[longbow]

Well, I kinda figure small driving bands might engrave easier with zinc being so hard so maybe 73-770ST tumble lube style grooves or maybe even better, get Tom to leave out the middle band on your 73-770S or make all three driving bands a little narrower.

Maybe someone has experience and can correct me but I have to think that less bore contact would be a good thing with zinc.

Just my thoughts. Of course those thought got a little addled with recoil this weekend too so take it for what it's worth.

Longbow

[Cap'n Morgan]

Hogtamer, the shrinkage when pouring into a can will happen in the center of the cast, leaving a cavity or dimple. The outside measurements will still follow "normal" shrinking rules (0.5 - 1%)

If I were to make a mold for a zinc slug I would probably make the mold a nose-pour design and do away with the sprue plate by making the sprue part of the slug. The slugs could then be cast quickly (keeping the mold hot) and the sprues later be cut with a hacksaw after the slugs had cooled.

I would also recommend several thin driving bands. I use this for solid brass bullets and the driving bands makes up for only about 25-30% of the total bearing surface.

[Hogtamer]

Ok, regrouped and this mold ordered along with Zamak 3 from Rotometals. Put advice here to work. Thanks to all so now we'll see if this works in a few weeks! Our big archery event this weekend so off to "cast" some arrows!
http://www.accuratemolds.com/bullet_...73-770ST-D.png