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cellargun
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bullet/mold dimensions
Jan 7th, 2026 at 3:37pm
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Has anyone used a Lyman 375248 or 375449 bullet mold? 
While the nominal size is .375, what diameter can you expect for an as cast bullet with 20/1 alloy?

For the unasked question, it's certified alloy, not random lead like substances tossed in a pot with some solder. 

I'm aware that melt and mold temperatures can influence the final size so I'm looking for personal experiences, not theoretical.
Thanks, Richard
  
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Duck_Rider
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Re: bullet/mold dimensions
Reply #1 - Jan 7th, 2026 at 4:46pm
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I have and use both molds. My 375248 cast .378 the 375449 cast .376 with my 1:20 mix.
Harry
  
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oneatatime
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Re: bullet/mold dimensions
Reply #2 - Jan 7th, 2026 at 8:34pm
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Just as a little more information - "375xxx" molds made in the days when the nominal groove size for a "38" (like a 38-55) was .379 may cast larger than relatively current "375xxx" molds now that "38" barrel grooves are mostly standard .375. Ergo, older Lyman "375xxx" molds may cast larger than current molds of the same number.
  
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cellargun
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Re: bullet/mold dimensions
Reply #3 - yesterday at 8:34am
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Duck_Rider wrote on Jan 7th, 2026 at 4:46pm:
I have and use both molds. My 375248 cast .378 the 375449 cast .376 with my 1:20 mix.
Harry

Thanks. As cast at .378 would be perfect, .376 not so perfect for my application.
  
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cellargun
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Re: bullet/mold dimensions
Reply #4 - yesterday at 8:39am
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oneatatime wrote on Jan 7th, 2026 at 8:34pm:
Just as a little more information - "375xxx" molds made in the days when the nominal groove size for a "38" (like a 38-55) was .379 may cast larger than relatively current "375xxx" molds now that "38" barrel grooves are mostly standard .375. Ergo, older Lyman "375xxx" molds may cast larger than current molds of the same number.

Thanks. I was thinking along the same lines. Wear on the cherry also enters in the equation. Not having a mold in hand or knowing its age makes buying one on eBay or some such site a crap shoot.
  
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oneatatime
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Re: bullet/mold dimensions
Reply #5 - yesterday at 1:31pm
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At least some Lyman molds are marked with the year (2 digits) of production.
  
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cellargun
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Re: bullet/mold dimensions
Reply #6 - yesterday at 4:30pm
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oneatatime wrote yesterday at 1:31pm:
At least some Lyman molds are marked with the year (2 digits) of production.

Knowing some are so marked makes me wonder how old is old enough to be sure of getting one of the larger molds?
  
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oneatatime
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Re: bullet/mold dimensions
Reply #7 - yesterday at 8:34pm
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For my 38-55 Uberti, which maintained the original .379 barrel, I found a dual cavity NEI mold (379xxx/yyy) that cast a 245 grain round nose and a 310 grain spitzer. Both were gas checks. I don't use that one anymore as I wanted a heavier plain base so I ordered one from Accurate. I should put the NEI on the For Sale list as I have run out of space for molds.
  
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cellargun
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Re: bullet/mold dimensions
Reply #8 - Today at 12:07am
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oneatatime wrote yesterday at 8:34pm:
For my 38-55 Uberti, which maintained the original .379 barrel, I found a dual cavity NEI mold (379xxx/yyy) that cast a 245 grain round nose and a 310 grain spitzer. Both were gas checks. I don't use that one anymore as I wanted a heavier plain base so I ordered one from Accurate. I should put the NEI on the For Sale list as I have run out of space for molds.

After a guy on eBay gave me the brush off by refusing to measure his molds saying calipers “aren’t accurate to within .005” and  “would scratch them”, along with some other nonsense, Accurate will be getting my business once again.
  
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calledflyer
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Re: bullet/mold dimensions
Reply #9 - Today at 9:28am
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normal calipers don't give accurate readings on the inside anyhow.
  
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marlinguy
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Re: bullet/mold dimensions
Reply #10 - Today at 11:17am
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calledflyer wrote Today at 9:28am:
normal calipers don't give accurate readings on the inside anyhow.


I don't consider dial calipers accurate enough for inside measurements either. And I don't measure bullets with them either. I prefer a micrometer reading as I've compared my mic to my calipers and I know the micrometer is more accurate.
  
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cellargun
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Re: bullet/mold dimensions
Reply #11 - Today at 1:40pm
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marlinguy wrote Today at 11:17am:
calledflyer wrote Today at 9:28am:
normal calipers don't give accurate readings on the inside anyhow.


I don't consider dial calipers accurate enough for inside measurements either. And I don't measure bullets with them either. I prefer a micrometer reading as I've compared my mic to my calipers and I know the micrometer is more accurate.

After 50 years of machine shop work I know a micrometer is more accurate than calipers, inside or outside. 
I also know with calipers used correctly, you can(should) get within .001, and certainly closer than the .005 error factor the guy claimed. 
If you don't trust what the dial says, measure across the tips with a micrometer. You can also use a small hole gauge and a micrometer. 
Duck Rider mentioned 2 Lyman molds with a 375 prefix. One drops at .378, the other at .376, so I thought asking for a measurement was a fair request since the seller has a no refund, no return policy.
There are any number of ways to take a measurement, but he chose to do nothing.
  
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Duck_Rider
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Re: bullet/mold dimensions
Reply #12 - Today at 2:03pm
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I can muddy the water a little further I also have a Lyman 375296 that drops .382
Harry
  
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