Rifling Questions...

[Spotted Bull]

OK, what is the main difference, besides the obvious, in square bottom rifling and round bottom rifling?  What are the advantages or disadvantages of them?  Which do you prefer?

[Two Steps]

RB, if you can get a copy of the Sep/Oct Muzzleloader mag, there is an article by Fred Stutzenberger and Brian Turpin on this subject that you may find interesting.
Al

[dbm]

Captain John Boucher of the Surrey Rifle Volunteers was a prolific writer on military and shooting subjects in the 1850s/60s. He advocated for the military a .50 cal, 5 grooved rifling of 1:60 twist. The rifling eliminated any square edges. He recommended it to the War Office in 1853 and again in 1855 but it was not adopted. The rifle fired a cylindro-conoidal bullet that was fitted with a flat disc of thin iron it aid expansion.

The simplest form of round bottomed rifling was Lancaster's oval bore. This was adopted by the Royal Sappers and Miners/Royal Engineers for a carbine in 1855. It was gain twist.

In 1863 the War Office report on Small-bore Rifles reported favourably on the Lancaster oval bore and recommened its adoption over the Enfield form of rifling.

William Metford developed a form of segmental rifling that eliminated all square edges. This saw great success in long range rifle matches where paper patched bullets were used. This saw particular success in the military breech loader matches held at the Wimbledon in the latter part of the 19th century but is outside the scope of this forum.

As to the merits or historical use for PRB I can't offer any comment.

David

[LRB]

Most target competitors like square grooves. Most hunters/common shooters like round bottom. Round bottom easier to clean, easier to load. Square groove more accurate, but only enough to be important to serious  competitors. Round bottom, very accurate, but square groove usually has a slight  edge on accuracy. The common shooter firing from the shoulder, would likely never see a difference.

[Two Steps]

In the above article, their tests showed that the round bottomed rifling, over the whole range of powder charges tested, had a slight edge.  The Rd bottom produced a group average of about 1.7 inches center to center while the Sq bottomed rifling averaged about 2.0 inches (this at 50yds).
Al

[LRB]

I don't think a test using only one barrel of each type could be considered conclusive. A deviation of .3" could be expected between two barrels of the same type. However, I favor the round bottom grooving myself for it's other virtues.

[pathfinder]

I prefer round bottom for ease of cleaning and it's prettier.