1911 45 ACP case length & headspace questions
Sorry for the length of this post... I'm having a little trouble understanding the relationship between a 1911's headspace and its ideal case length for match grade handloads. Am loading for a Les Baer Custom 1911.
I saw a graphic on another post yesterday but can't find it today. It showed a drawing of four 1911 45 ACP barrels with cases inserted and captions indicating if case length was too long, too little or somewhere inbetween.
For Bullseye match shooting I've just started making up some test loads for its 45 ACP cartridge with charges ranging from 4.2 gr. up to 4.6 gr. of WST powder with a Dardas 200 gr. LSWC bullet. Have tested functionality with case lengths of .889" and .892" with cartridge OAL of 1.235" on both. Hornady manual and Lyman Cast Bullet Handbook both say to trim cases to .888, while the Speer Manual states .893". After taper crimp my case mouth diameter is .472", which is based on the Mike Venturino calculation that's stated in the Lyman Cast Bullet Handbook (i.e. which in my case for my .451 bullets and casings is comes out to bullet dia. + case rim thickness = .476 -.004 = what should be an appropriate taper crimp dia. of .472.
Both case lengths feed and extract without fault. Completed cartridges with cases trimmed to .892 drop easily into chamber and casehead sits flush with the little milled extension coming off the back edge of barrel that the bolt face contacts (sorry but I don't know what that part of the barrel is called).
With a .892" case length, the bearing surface of the LSWC bullet is barely exposed past the case mouth. With .889 it's marginally more.
Based on the above, all would appear well and good. However, used my caliper to measure depth of chamber from the top of the little milled extension coming off the back edge of the barrel where to the bolt face contacts all the way down to the little lip inside the chamber that the case mouth is supposed to headspace against and get a measurement of .900".
So my question is that if that headspace lip down inside the barrel chamber is .900" deep and my case length is .892", then shouldn't the case head be .008" below the little milled extension coming off the back edge of barrel that the bolt face contacts? If so, shouldn't a cartridge with a .892" case length drop farther down into the barrel than what I've described?
Another question is that if the 45 ACP headspaces on the case mouth, and the max. case length for this cartridge is .898", then why would the Hornady manual want you to trim the case to .888", thereby leaving a full .010" gap between the case head and the bolt face, because won't this excess headspace effect accuracy?
Thanks for any help anyone can provide.