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View Full Version : Marks crossways on the lands ?



Old Gunner
11-13-2009, 10:41 AM
So far every Marling, Glenfield, or Stevens rifles I've examined , at least those made since the early seventies, has visible crossways marks or striations on the lands. This doesn't seem to have affected accuracy of those rifles, but these aren't target grade barrels.

Every older .22 rimfire rifle I've examined had no such markings, the lands finely polished without any markings. This could be due to wear but I figure its more likely that the methods used to bore and rifle back then didn't leave such marks.

I'd once read that the crossways markings were beneficial, in reducing bullet friction and preventing leading, but that may have been manufacturers hype.
It does sound logical on the surface, the striations acting like the honing of a cylinder to hold lubes, and the uneven surface letting the bullet slide past on the built up lube deposits.
In a way the action would be similar to the recorded results of firing a lightly surface pitted or "seasoned" bore compared to a fresh highly polished bore, the former showing an increase in velocity, at least when lubed lead bullets were in use.

I had not given this much thought till discussions on efficacy of fire lapping came up. That and some bore scope images I ran across which showed the same markings found in some centerfire barrels.
The text with those photos stated that the marks were left over from the boring and reaming process and that button rifling did not remove them but rather crushed them so that any flash was angled towards the muzzle.
A barrel turned from a blank that had been reversed ended up with the flash pointed the wrong way and caused excessive metal fouling and higher pressures.

In the old days of cut rifling any such striations should have been either worn away by passage of the cherry or spud, and if not following up by lead lapping would have polished them away.

Any thoughts on this, and have you encountered this situation before?

crb
11-13-2009, 12:26 PM
One of my buds had a Walther bbl installed on a 541 25 years ago. He says he has fired at least 1000 rounds a year through that bbl. It still has uniform reamer marks the full length of the lands so I personally don't believe that a lead bullet will do anything more than a polish job on a smooth bbl. On a rough bbl I think the bullet gets stripped and very little is done to the rough bore.

Any polishing a bullet might do to even the smoothest bbl is offset by the 6:00 bore erosion.

Old Gunner
11-13-2009, 04:03 PM
Polishing of the lands of the older barrels I mentioned would have been due to the atomized glass added to the older corrisive primer compounds. this mixed with bullet lube would have had much the same effect as lead lapping using a polishing compound.

Cut rifling would remove the portion of the reamer marks over what would then become the grooves, leaving lengthwise striations, such as those used to ID a bullet in a forensic examination. The spud riding the bore would tend to wear away any very shallow marks.

The British sometimes used a Ball burnishing process to upgrade standard .303 barrels for target use. These were called "nickel less" or non nickeling" bores and stamped at the muzzle to show they'd gone through the process.
A series of polished and hardened steel balls were pushed down the bore by a hydraulic ram. The hardened balls burnished the surface of the lands only, to remove any reamer marks or burrs, and any previous marks left by a cleaning rod.
If any deeper marks were left the edge would be turned forwards to reduce chances of it catching and stripping shreds of jacket materials.
This is said to have made cleanup much easier and prevented Cupro-Nickel build up on the lands.
The bore across the lands was increased from .303 to .304 by the process, and edges of the lands were sharpened a bit.


I have seen a few very very old .22 rimfire bores that showed the lands to be very gray and worn, yet still flat on top, while the grooves were black and rough looking from the old corrosive ammo. Worn lands looked to be about half as tall as they should be. the barrels still shot fairly well but not with any high degree of accuracy, and the shallowed grooves choked with fouling easily. this seemed to be more common with auto loaders.

crb
11-13-2009, 04:41 PM
I recently had a 17 cal bbl that had consistent crossways grooves for the full length and full circumference of the bore. The grooves appeared to be the same depth on top of the lands and down in the grooves. You would think somebody had a cnc boring machine that cut the lands and grooves at the same time. I don't have any idea how they managed it. I even sectioned a short length so I could look at the surface directly. It truly looked like a fine tooth metal file with the cross section of a rifle bbl's bore.

I sent it back.

Madrox
11-13-2009, 05:22 PM
I'd once read that the crossways markings were beneficial, in reducing bullet friction and preventing leading, but that may have been manufacturers hype.
It does sound logical on the surface, the striations acting like the honing of a cylinder to hold lubes, and the uneven surface letting the bullet slide past on the built up lube deposits.

In a way the action would be similar to the recorded results of firing a lightly surface pitted or "seasoned" bore compared to a fresh highly polished bore, the former showing an increase in velocity, at least when lubed lead bullets were in use.



Must be why my file doesn't work on lead.