Is a 38 bullet bigger than a 45 bullet?
When people talk of a 38, they mean .38 caliber, or 38/100th of
an inch.
Likewise, a 45 is .45 caliber or 45/100th of an inch.
45 > 38 so a 45 has a larger diameter.
However, there are different lengths for each of those calibers,
so a .38 Special is longer than a .45 ACP so in THAT sense, a 38 is
larger (longer) than a 45.