Cast some 440s and 490s. They too varied a bit so normal is my decision. I test fired 440 in 45cal,measures 456, with 2 010 patches. Patch against powder did not burn as bad. 2nd test I shot through a piece of pine 1x. Patch against ball was fried doughnut. Might be because of the wood, not sure. First was in moist dirt and I'm sure it cooled quickly. 2nd was flung into the air.It is doubtful that Lee cut the mold the wrong size. After they cut the mold they put a polished carbide ball of exact size in the mold and bring the halves together in a hydrolic press.
They may use Lyman #2 alloy to give the as cast diameter. It casts slightly smaller than pure lead.
Using thin patches will cause them to burn through in the middle. Bad.... A thin patch, say under 0.010" is asking for trouble. I have had no success with thin patches. If you want to experiment with them put a wad under the ball/patch.
I tend toward smaller balls and thicker patches. The patches will be tougher, hold more lube, and be more forgiving to load. They will be less likely to have have damaging blow by. I have shot good groups with smaller balls and denim (0.032") patches but never with patches under 0.010"
The reason that the common balls/ patches for 50 is 0.490" and the patches sold in bulk are about 0.015", is because it works for almost everyone, at least reasonably well.
It is doubtful that Lee cut the mold the wrong size.
Using thin patches will cause them to burn through in the middle.
NOT the patch thickness but the seal and fit. As a ball gets larger the patch will get thinner and will not burn if you still seal.OK, when I have used very thin patched they have burned through in the middle. Your mileage obviously varies.
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