Mountain Molds - Diameter Accuracy

[30yrcaster]

Hello,

I'm new to this forum and it looks like there's alot of good traffic here.

It looks great that you can design your own molds at Mountain Molds. If I were to order a mold for say paper patched bullets where I need the bullet to be used "AS CAST" for a certain diameter ie. .440, would I actually get a mold that would put them out that size for a given alloy? I see his design software shows 0 to +.002 tolerance. An extra .002 could be a problem.

There's been mostly positive posts here on Mountain Molds.

Thanks!!

[Bass Ackward]

Hello,

I'm new to this forum and it looks like there's alot of good traffic here.

It looks great that you can design your own molds at Mountain Molds. If I were to order a mold for say paper patched bullets where I need the bullet to be used "AS CAST" for a certain diameter ie. .440, would I actually get a mold that would put them out that size for a given alloy? I see his design software shows 0 to +.002 tolerance. An extra .002 could be a problem.

There's been mostly positive posts here on Mountain Molds.

Thanks!!


30yrcaster,

My experience is that Dan's accuracy is dependent on the method and temperature of his mixes. And how hot you run your moulds. Remember he tests each one, but not for anywhere near the time you will probably use it. If you mold out of that temperature range, you get the plus or minus. And .... certain mould materials also add to the shift.

Go to Dan's forum and tell him what you are thinking and how you want to mold and what mold material you are "thinking" of purchasing. He will still hem and haw a little and claim the .002, but you will be a lot closer than if you go your own way.

Remember that you can always adjust your temperature down from his to get larger or spay molly in the cavities to reduce by .001. So you will be close.

[Buckshot]

................A thousandth is a tiny little thing. I can see in some applications where a thousandth would be a big problem. Lead alloys unless blended from pure ingredients may vary quite a bit in their shrinkage from what takes as 'Book' for known industry alloys like linotype, or foundry type. Add in a tolerance in cutting the cavity and there is a thousandth or so, if not twice that.

As BA said, if the slug is a trifle too large on OD, spray the cavity with something like Midway mould Dropout. Alloy temps at casting will affect dropping OD.

I have an article by Henry Beverage concerning accuracy potential with a rifle he had. He wanted to use the Lyman 311284 design. He bought FIVE brand new Lyman moulds from places as far apart as possible in order to try and get one as close to perfect to his needs as possible. He said he figured he could sell off the ones he didn't need.

Remember too that you can alter the final OD of your patched slug by sizing it a little before or after patching it.

................Buckshot

[30yrcaster]

Thanks for the ideas!!

Is there a rule of thumb on how many degrees will change the diameter X number of thousandths? 50 degrees? 100 degrees?

Thanks!!

[Bass Ackward]

Thanks for the ideas!!

Is there a rule of thumb on how many degrees will change the diameter X number of thousandths? 50 degrees? 100 degrees?

Thanks!!


One example I have is from the 35 caliber, 250s I just molded. I was at 800 degrees and got .3596. At 725 once I was throwing almost 361. This was a brass mold. A 311284 only yields about .0005 bigger if you cool down the mix and or cast more slowly. It varries based on the mold material and obviously is greater in the larger calibers.

But I never read any set guidlines that I can point you to. In fact, I have an aluminum mold by LBT that actually opens up the hotter it gets. That is up to 800 degrees. I .... never had it over that that I can recall. The guys that get in trouble the most are the pure lead boys that super heat. Sometimes they experience warping too. Brass is bad about that above 900. If I was going for a mold to run hot, I would probably go steel. But I don't own too many steel molds anymore.

I would still ask Dan. Just go to his site and scroll down the menus to the left. His forum is on the bottom. He could tell ya more.

Anyway, welcome to the board.

[nighthunter]

www.lasc.us has some good info under cast bullets that tells about alloy effect on final cast size. You could check and see if they cover temperature effects. http://www.lasc.us/CastBulletNotes.htm is the exact link.
Nighthunter

[Char-Gar]

It has been about a year, since I had Dan (Mountain Molds) make one for me. He promises the bullets to be +/- .001 of spec. He told me that if I just could not accept a bullet .001 smaller than spec, then order the mold .002 larger than the smallest I would allow. I have three of his molds and all three have been "spot on" to the specs I have sent. So, I just say a prayer to the lead gods and send him the specs I want. So far it has worked for me.