I recently loaded some Oregon Trails Lasercast 240 gr SWC bullets with 7grs of Unique and got excellent accuracy out of my 4" 629. I plan on moving up to some full power loads in my 29.
These bullets measure .431 according to the manufacturer but others claim a diameter of .429 or .430 depending on bullet type or maker. Why the differences?

Just depends on the dimension to which the manufacturer sizes the bullet. I'll let others tell you about chamber mouth dimensions and barrel slugging and why that could be important.

If you get excellent accuracy and no leading in your barrel, don't worry about it, everything is at it should be.

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Where we go one, we go all

My 1980-1990 44's have somewhat larger chamber throats than
the modern ones which more closely adhere to the .429 - .430 standard.
I have found that the LazerCasts actually mike .432 and work very
well in the 624's and 629's from the '80s.

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Nemo