What am I looking at??

[JohnMill]

I do not understand the lateral tool marks in both land and groove. I would think one of them should be linear ( the groove?). Not a hand lapped barrel. That is why I'm looking to learn how to pour a lead lap for a barrel. Do not want tool marks like that on my barrels, new or old.

 

[J E Custom]

I do not understand the lateral tool marks in both land and groove. I would think one of them should be linear ( the groove?). Not a hand lapped barrel. That is why I'm looking to learn how to pour a lead lap for a barrel. Do not want tool marks like that on my barrels, new or old.

All tool marks are a sign that the drilling process was not done correctly and in order to remove these marks, two much material would have to be removed increasing the bore diameter beyond acceptable limits for the bullet to seal the gases causing an accuracy and velocity loss.

For the buttoned rifling the bore has to be reamed to an exact size that will allow the material in the grove to be displaced (Forged) and added to the lands so there will be little if any tool marks. Cut rifling requires the land diameter to be very close to the finished land height so that the bore diameter (Groove Diameter) can be cut to the correct bore diameter without altering land height. except for the final lapping, both dimensions are very close to SAMMI dimensions before lapping. Lapping is then used to apply a final finish, (Not to re size the lands and bore).

Factory rifle barrels look this way because these steps are not taken and the drilling process is near the finish dimension. lapping a factory will increase the bore and land diameter to beyond the needed dimensions if over done, so it is considered a last resort.

The premier barrel makers adjust there reaming to end up slightly larger in both diameters so that lapping will bring the dimensions in to exact diameters.

Tool marks are not realy that bad for accuracy if there size is correct but they do contribute to copper and carbon fouling if not cleaned often. "BUT" accuracy will never be as good as a barrel with the proper finish and no tool marks.

J E CUSTOM

 

[JohnMill]

Yes but my question is how do the drill marks appear in the bottom of the groove when the material that was drilled/reamed was displaced by a pulled button or removed by a rifling cutter. The lateral marks at the bottom of the groove should not be there and I wondered how they survived the process. That's all I was saying.

 

[Gord0]

Yes but my question is how do the drill marks appear in the bottom of the groove when the material that was drilled/reamed was displaced by a pulled button or removed by a rifling cutter. The lateral marks at the bottom of the groove should not be there and I wondered how they survived the process. That's all I was saying.

They're there because they were there before it was button rifled. The button does iton some of that out, but not much.