Confused......

[xd45forever]

I have a 4th edition lyman castboolit manual and was looking for a 405 grain mold and the manual said the lyman 457193 mold was 405 gra in so I found one and started casting and the bullets I was getting were 420 grain! OK fine no big deal I'll use them but my manual doesn't give me load data for a 420 grain in a marlin lever. I downloaded an older lyman manual and it says the 457193 is 420 grain and gives load data for the marlin lever, what gives?

[pworley1]

The alloy you use can change the weight of that size bullet several grains. The more tin and antimony in the mix the lighter the weight. Unless you are wanting to load absolute max loads, don't worry about the weight difference.

[TurnipEaterDown]

Your bullet weight changes because of alloy percentage change. Heavier bullet than listed on mold: More lead in alloy. Lighter bullet than mold listed: Often more Antimony in alloy than the mold is quoted to throw. Tin is lighter too, but most alloys use small percentages. Contaminants can do this too, but you should see something in the melt. Poorly cast bullets (voids) will be lighter too, but if you continuously get light bullets from voids, you will likely soon see issue around the sprue.

Use the data for the bullet Mold. Not an equivalent weight bullet.
Usually the weight variance from nominal mold throw weight doesn't make much difference. There could be some exceptions if you were to run at absolute max pressure or the mold was had a quoted weight w/ high alloy percentages (can't think of any maker that does that).
Different molds with a weight quoted as what you cast out of your mold may have a very different case intrusion length, and can cause issue w/ data swap, particularly w/ high pressure handguns.

[Mal Paso]

I have a 4th edition lyman castboolit manual and was looking for a 405 grain mold and the manual said the lyman 457193 mold was 405 gra in so I found one and started casting and the bullets I was getting were 420 grain! OK fine no big deal I'll use them but my manual doesn't give me load data for a 420 grain in a marlin lever. I downloaded an older lyman manual and it says the 457193 is 420 grain and gives load data for the marlin lever, what gives?

The 4th Edition of the Cast Bullet Handbook has errors and mistakes not included in previous versions.

[Geezer in NH]

405 would be Lyman #2 alloy, yours is less hard.

[Winger Ed.]

As sad-- That 405 figure is for Lyman #2 alloy.

My single cavity RCBS FP mold in .45 cal 405 gr casts out at 424 also with my cobbled together mystery alloy.
19 gr sounds like a lot, but it's only 5% on the heavy side.

I load right in the middle out of the Lyman cast book for the Marlins & Winchester .45-70s with IMR 3031 or 4198.

Next time around, I'll take it down to the trapdoor speeds.

[softpoint]

My RCBS .45 rifle molds all cast heavier than the stated weight with my alloy. The 300 casts 314, the 325 casts 350, the 405, 424, and the 500, 514. It's no big deal. Different alloys.

[DocSavage]

I would reduce the starting powder charge by 10% and work up from there. The Marlin can handle heavier charges of powder than a trapdoor.