When used in front of a blackpowder charge, paper-patched bullets work best when designed significantly smaller than groove diameter.With such loads, when the charge ignites, the relatively rapid increase in chamber pressure accelerates the bullet so fast that the core begins to swell (obturate) before the bullet moves significantly.
DISCLAIMER: All reloading data in this article is for informational purposes only.
Starline Brass and the author accept no responsibility for use of the data in this article. Synopsis: The 38-55 Winchester Center Fire (WCF) is a unique example among metallic cartridges — through almost 125 years of production, until quite recently, 38-55 cases had evidently never been made correctly for use with conventional bullets. For most shooters loading conventional cast bullets in guns with standard 38-55 bores and correctly cut chambers, using the 2.125-inch long, thin-necked, Starline 38-55 cases can provide a significant accuracy improvement.
This article, including pictures and captions, first published in Precision Shooting magazine (now defunct). How it Started, My Hypothesis In 1879, Ballard introduced the 38-50, which featured a 2-inch-long case (many tapered cases of that era were named not for capacity but for length and for that reason many were made to specific lengths based upon inches and fractions of one inch — usually, in half- quarter- or eighth-inch increments).
But, this convention was often supplemented by listing the charge used, rather than the case length.
For example, the Sharps Rifle Company listed the chambering as 50-2½" Sharps but marketed the ammunition as 50-90 Sharps.
(Cartridge naming has always been confused and confusing, it seems.)Ballard evidently viewed the 38-50 chambering strictly as a target-shooting combination.
For this reason, it sized the chamber to take best advantage of cartridges loaded with paper-patched bullets.
In that era, paper-patched bullets were the most accurate design known for cartridge loading.
It is also unlikely that such a bullet would rapidly and symmetrically shed the paper jacket after exiting the muzzle (because the paper would not be adequately stretched and weakened by bullet obturation); this too would hamper accuracy.
In every blackpowder-era chamber that I have seen that was designed for use with cartridges using paper-patched bullets, it seems that the design goal was to hold the paper-patched bullet centered in a case neck that fit the chamber without much expansion and then to allow the bullet to expand into the chamber throat as it exited the case mouth, so that, as it entered into the rifling, it was already well centered within with the bore and the patch was well stretched.
Whatever the logic might have been, it worked and these guns and loads were phenomenally accurate.