Rifling groove shape

[Bob Ekes]

In reading an add for barrels (might have been Rayle barrels, I think) They said that they carried both round bottom rifling grooves and square bottom rifling grooves. Why the difference? Does one give a better seal for the patch? Does one handle fouling better? Is one more accurate? Just curious. Any info?

 

[jimeckersley]

Several barrel makers including Getz, Rice, Rayle, & Colrain make a round bottom groove. Many people like the round bottom grooves because they're very easy to clean and some say, have less fouling accumulation.

Accuracy? I don't know anyone who has more than an opinion on that question. I'm sure you'll be offered a few of them. My personal preference is for the square cut wide groove / narrow land system. But, if someone offered be a free rounded groove barrel, I'd keep it.

 

[Randy]

It seems to make sense that squishing the patch into a round bottomed rifleing groove would seal better ( or at least easier) than a square bottomed groove. ( no sharp corner to plug up) I have both and can't tell the difference. I don't know of any scientific studies, but round just sounds like a good idea.

 

[LRB]

In general, square lands are a tad more accurate, but off the shoulder, you would not know. Don Getz shoots chunk guns, and his are square grooved.

 

[Randy]

Most chunk guns use an oversized projectile and thin patch and have relatively shallow rifle grooves. This combination is quite different than what you would normally load for hunting or off-hand shooting. I still expect you can fill up and seal a round bottomed groove easier than square with the "loose" fitting ball and patch combination that many of us shoot. would be good to get some input from one of the barrel makers here. It may be that any rifleing configuration will work well with the right components. The chunk gun fellows certainly know something about accuracy.

 

[Erzulis boat]

There might be another factor to consider. I do not make rifle barrels for a living, so this is pure speculation.

I manufacture a splined assembly (very similar to a rifle barrel) that is constructed from Invar 36 that is broached with 6 large splines. I had the tool manufactured with "round bottom" grooves just like a Colerain barrel, why? Because the broach will last for many operations because it "cuts" easier, and the PSI required to ram it through is less than if the splines were "square". Easier on the tool, and on the operation. Granted, I still need a 90 degree shoulder at the root, but the rounded extremity increases tool life.

When I saw a Colerain, I immediately assumed that this was the reasoning, not until later did I hear of this "less fouling etc." thing.

I do not make barrels, so I could be wrong.

 

[manyirons]

Good thought on the round bottom broach and might be applicable if the barrel WERE broached.

Local barrelmaker here does cut rifling, almost infintismal amount of material removed per pass with a single point or what he also calls a "Hook" cutter.

Broach forms everything in one pass, this rifling requires (I'm guessing) probably twenty passes per groove and he could pull it by hand if he wanted.