I think the original Author of the Screw-Barreled Jaegers, was misinformed. I cannot see any practical benefit to a barrel in that configuration in that era.
My guess, is it was hearsay. Not verifiable, unless something else has been written on the subject. You have to remember, that during this same period, a great many of the populace still thought that standing garbage, created flies, and that Kings were living Gods.
Now, if we're talking 20th Century Sniper rifles,
yes, I did own a change barrel .308 - .300 Win. Mag.?!?!
The only other explanation, to me possibly would be a rifle that would have a new barrel installed, in a different caliber, along with a new the plug being re-installed. Say something like a .58 cal. being converted to a .62 or .75?
Something that an experienced Armorer of the period, would be able to do.
Just my thinking out loud...