You're right, AkMile - the grooves also help with a fouling deposit area, however they also allow blowby of powder gasses, which allows gas cutting of wads, balls (unless patched) or shot.

Straight rifling has actually been cut into bores since the 16th century - it is not something new to the late 19th century.

Over the years, straight rifling has been used for different reasons.

The reason I mentioned above is as valid as any other - it allowed a shotgun (preferred by Swede farmers) to legally shoot moose, yet they still only needed one gun which was mostly used with shot. One merely carried a couple round ball loads and if a moose presented itself, bang!

If slightly choked as well, the patterns would be improved over cylinder boring, of course, without further injuring ball shooting. They were close range guns with ball - ie; 75 to 80yards. That can also be handled easily with smooth bores and round balls with good load development, but smooth bores had been declared illegal - hence straight rifling.

If I wanted to shoot and hunt with round ball, I would not purchase a rifle without more normal twisted rifling.

At some point, the round ball, from straight rifling, or smooth bore, takes on a spin and careens off to one side, down, and never in the same direction shot to shot. A normally loaded smoothbore with loose ball, induces spin while inside the bore, which limits it's accuracy range to even less than 50yards. Given a good charge, the straight rifling will deliver the ball as a knuckle ball, non spinning, which will happen, given enough time of flight.

However, if one calls his the moose to his blind, 20 yard shots are the norm. and either will work just fine.

Many years ago, my brother shot a nice big dry cow moose (no calf), making a perfect lung shot at 95 to 100yards distance. Using a Brown Bess Flintlock Musket, the cloth patched 600gr. pure lead ball flew true to the mark dropping the cow in 4 steps. The ball was perfectly expanded to over an inch in diameter against the off-side hide. I still have that ball - somewhere?

They'll work at close range - properly loaded- straight rifled or smooth.