"...measurements are somewhat subjective..."
Well, measurements themselves are precise but what we humans assume about them and/or do with those assumptions is sometimes subjective.
You measuring activity got my curiosity up...at age 63, 25 years of which trap/skeet shooting and reloading were a huge part of my life, I've never personally 'measured' a shotgun shell in all that time...the 2+3/4" shells looked about like 2+3/4" should look and all the guns I had called for 2+3/4" or 3" shells, life was good.
So I just now measured a new unfired & a once fired Win-AA .12ga 2+3/4" (70mm) hull:
New unfired = 2+5/16"...barely over 2+1/4"
Once fired = 2+11/16"...still shorter than 2+3/4" even AFTER being opened.
Compared to the exact chamber measurements I made last night, these hull measurements make it clear that what we call 2+3/4" plastic star crimped hulls will work perfectly in this Colt.
