Over all cartridge length?

The .45 acp cartridges that I just loaded seemed shorter than the factory ammo that I have with a similar bullet.  The factory ammo OAL is 1.212".  It's a Winchester white box, 185 gr. FMJ with a flat nose.  The Lyman Reloading Handbook calls for an OAL of 1.135" for a similar bullet.  Why the difference and is it critical?

Winchester's bullet might look similar, but it might not be the same.  Winchester did the testing on their bullet, and they are responsible for that round as a complete package.  For your reloads, follow the book recipes first.  When you have mastered reloading, you might try disassembling rounds to replicate them--but you are not ready yet, grasshopper.

Loads are tested NOT at the "ideal" COL but at what is really a minimum COL for bullet/cartridge. This way, when you work up the best COL for your gun, it will almost always be longer than the manual's--which is a LOT safer that you loading to a shorter COL than in the manual.
In fact, I have seen a manual that specified "max COL." I wrote and found that what they meant, and never explained, was that it was the maximum COL that SAAMI specified for TESTING ONLY so factory and reloaded ammo would almost always have a LONGER, and thus safer, COL. Testing aims for a worst case condition.
Just for information, the main variables that determine the COL range for a given gun are:
bullet geometry, particularly the ogive
the magazine and when the lips release the round
the feed ramp
and
the chamber throat length.
The manual does not specify optimized loads, it simply gives the reloader a place to start.