tokguy: First firearm in question was an 1873 Colt SAA...dated circa 1889. Revolver belongs to a collector friend of mine. Originally chambered in "Short" Colt, then converted sometime post-1900. Gunsmith conversion, not factory. Bullet used was cast, .376" outside- lubed heel-type, from custom mold. 3F Swiss bp for propellant.**
Also: .358"-.360" hollow-based bullets were tried, with some success.
New Starline, Long Colt brass was annealed prior to sizing/loading.
Note: .38 'Short' Colt cartridges also loaded and shot from this same revolver. Same bullet.
From same collection: Mod. 1892 Colt. This revolver features later bore diameter reduction to .357". This time, .358" bullet. Cast: LRNFP, fully enclosed inside case.
Smokeless(Clays) for propellant. .Cut down, 38 Special brass chambers fine in this revolver. Likewise, Starline, Long Colt brass.
It bears mentioning that, firing the 'modern' version of the Short/Long Colt, in other .38 Special and .357 Mag-chambered revolvers, has also been trouble free. Aside from expected minor accuracy loss, due to long bullet jump from chamber to forcing cone (Short Colt, in particular).
I agree..."modern" iterations of the .38 Short/Long Colt cartridge , do vary somewhat from the originals. As you accurately describe, modern cartridges are more of a 'Short' .38 Special, than a true 'Colt' cartridge. Which may become troublesome to deal with when encountering the larger chambers. Still, with careful case prep, no problems to date(Knock on wood).
Al
**Note: Load data withheld for all cartridges tested.