i'am wanting to start casting my own bullets for a .45 colt. in my speer reloading book the bullets that the book call for start from .451 and go to .454. why so much differance

tradition?
for 45lc with CAST bullets, .453

Early 45 Colt groove sizes usually were larger, around 0.454" or more. 45 ACP and later 45 Colt groove sizes are more like 0.451"-0.452".

Reloading dies will be found with either size, it's worth checking your barrel's groove dia before purchase of dies and bullets.

BTW early Colts will have 45 Colt cylinder throats that are quite undersize (0.451" vs the needed 0.454") and will usually benefit from having them reamed a little larger.

This general subject is a mare's nest of conflicting dimensions and opinions, and really deserves a long dissertation.
Regards, Joe

quote:

Originally posted by J.D.Steele:
... it's worth checking your barrel's groove dia before purchase of dies and bullets....

+1

quote:

the book call for start from .451 and go to .454. why so much differance

Because the gun makers have made bores in those sizes.

Early 45colts had groove dia of 0.454". Currently manuf 45colts run 0.451"-0.452". With lead bullets, you size 0.001" over groove dia. For most, that is gonna be 0.452" for lead bullets. More confusion? Measure the throat dia of each chamber. The throat dia wants to match the groove dia for best results. If too small, polish larger, if too large, size to throat dia.