Shallow rifling good for jacketed but not for lead bullets?

[Thirties]

I was looking at revolvers the other day, and noticed a particular 2" Rossi .38spl had awful leading in the barrel. After the store owner cleaned her up a bit, I noticed the rifling was very shallow compared with the Colts, Rugers, and Smiths I'm used to seeing.

I've been shooting revolvers for maybe two years now, and I'd never seen such a leaded barrel as on that Rossi. I don't think I've ever seem any leading in a barrel. I shoot my own target loads, so I've never pushed the envelope with lead bullets. It looked like congeled black butter in there.

It later occured to me that the shallow rifling may have had something to do with the leading. Do deeper grooves mean less leading in revolvers? And if so, why would a gun be made with shallow grooves like that Rossi was? Do shallow groves shoot jacketed bullets better?

Any ideas about this?

 

[Delmar]

Not sure if its an issue-my Smith and Wesson M60 has pretty deep rifling and handles lead pretty well. On the other hand, my Colt Automatics have shallow rifling and also handle lead pretty well indeed.

 

[Quantrill]

Marlin's "micro-groove" rifling was the beginning of this train of thought. Supposedly, micro-groove rifles were not capable of shooting lead bullets accurately. I do not have a definiative answer for you as I do not have any micro-groove firearms but I have read articles from both sides of the fence from knowledgable folk. Quantrill

 

[Preacherman]

A lot depends on the hardness of the lead. Soft lead, pushed to high velocities, will "strip" in the barrel, causing severe leading. At low velocities, it's usually fine. On the other hand, hard lead at low velocities may not properly engage the rifling, which can lead to "tumbling" bullets and loss of accuracy: but at higher velocities, it's fine.

Micro-Groove rifling (Marlin's standard for many years) exhibited these problems. Their new Ballard-style rifling (fewer grooves, cut deeper) seems to eliminate them, whilst still being accurate with jacketed bullets.

 

[Thirties]

Funny you should mention Marlins with their micro-groove or their deep-cut Ballard riflings.

The new model 1894 Cowboy in .32H&R Mag is listed as having 6 groove rifling, but no mention of either Micro-grooce or Ballard type. Each other rifle on the page (page 9 in the 2005 catalog) lists "deep-cut Ballard-type" rifling in the barrels. (Mabe a typo? It happens)

So, I had seen that Rossi snub .38 with very bad leading and very shallow groove rifling; and, never having seen a Marlin with the Micro-groove (mine has the Ballard-type) rifling, I wondered if shallow rifling is particularly prone to leading, or not. Is the depth of the rifling a factor in leading?

I don't have years of shooting or gun experience. After seeing the leading in that Rossi barrel, I realize I'd never before seen a leaded barrel — I load target low velocity HBWC.

That's what I'm getting at with these questions . . .

. . . Merry Cristmas, folks!

 

[mete]

The problem with Marlin's micrgroove rifling was not that it wasn't accurate . Shallow rifling requires a much more careful choice of bullet hardness and bullet diameter to get the accuracy. Too many shooters used junk bullets and didn't get the accuracy so Marlin dumped the Microgroove.