Tooling marks in bore

[Rider47]

"Is the reduction or elimination of reamer marks in the barrel the only purpose of lapping?"
Primarily - Lapped barrels generally foul MUCH less than non-lapped barrels due to the smoother bore surface, and less bullet deformation/damage in the barrel also provides improved precision. Lapping can also be used to eliminate bore diameter imperfections, or to lap in a choke/taper as described previously.

"If lapping is a criteria of a "match barrel" it would seem to exclude barrels on rifles made by Anschutz, probably Walther and FWB also."
Yes - "factory" chrome-moly barrels are generally not considered "match" grade barrels.

 

[1588]

A borescope is a useful tool for a rifle that won't shoot well. If the rifle shoots well, there is no need to fret over machine marks in the barrel.

I ruined a good shooting 8mm Mauser by going to extra lengths to make the lands and grooves shiny. I turned a 1-1/2 MOA rifle into a shotgun disguised as a rifle.

 

[tomme boy]

@Frank Green I am talking to some people on another forum about this exact same thing in a savage barrel. Could you please tell us what these "chatter" marks are. These people just can not get through their heads what this is.

Thanks! Tom

 

[1588]

I've caused chatter marks on material I machined due to set up, trying to cut too fast, trying to cut too much material on each pass and the use of a dull tool.

On mass produced barrels, it is not unusual for you to see chatter marks on some of the finished barrels. If I have the opportunity to inspect more than one rifle of the same make and type, I try to select a barrel with the smoothest looking lands and grooves. Although, a few of the best shooting barrels I've owned had chatter marks.

 

[Frank Green]

tomme boy: You are almost correct. The marks in the images the OP posted are REAMER marks. Barrels are not button rifled after drilling without reaming to a final dimension. Virtually all barrels have these marks (button or cut rifled) until or unless these marks are lapped out. Low end barrelmakers do not lap these out. High end barrelmakers lap after reaming and before rifling and/or after rifling. Lapping is done by machines (i.e. Sunnen) and/or by hand.

Yes, no and maybe so......

Yes the marks in the original pictures in this thread are bore reamer marks. The deeper the bore reamer marks and when you pull or push a button thru the bore it just presses the marks down into the grooves. The rougher the marks the more the barrel is going to foul. The marks are in the opposite direction of bullet travel. So basically it will act like a file.

Not all barrel makers pre lap after bore reaming. I know of some gun makers/barrel makers that are so cheap they drill and just pull the button thru.

We pre lap before rifling (after reaming) and finish lap after rifling. All we do is cut rifling.

Later, Frank
Bartlein Barrels

 

[Frank Green]

"Chamber a round and pull it back out and you should see distinct rifling marks where it pushed it in the lands."
This will tend to indicate a match chamber, not necessarily a match barrel.

I disagree with the above statement. Reamer could have been ground shitty and you could be jamming/sticking bullets! or..... Just helped a customer last fall that a custom gunsmith supposedly cut a match chamber. It wouldn't even chamber box ammo or handloads. Looked like the gunsmith rough chambered it and used the roughing reamer to set the headspace but never finish chambered it. We ended up fixing the guys gun for him.

What is a match chamber to one person is different to another person.

When a customer asks me for a match chamber...I ask the customer to describe what that means to him? Tight throat diameter. Shorter throat? Longer throat? No turn case neck? Tight neck that you have to turn the case necks?

Pick your options.

Later, Frank
Bartlein Barrels

 

[Frank Green]

Button rifling displaces the material...it does not remove material from the bore/grooves during rifling.

Cut rifling you physically cut away the grooves. You don't touch the bore during rifling.

 

[accurate obsession]

Yes, no and maybe so......

Yes the marks in the original pictures in this thread are bore reamer marks. The deeper the bore reamer marks and when you pull or push a button thru the bore it just presses the marks down into the grooves. The rougher the marks the more the barrel is going to foul. The marks are in the opposite direction of bullet travel. So basically it will act like a file.

Not all barrel makers pre lap after bore reaming. I know of some gun makers/barrel makers that are so cheap they drill and just pull the button thru.

We pre lap before rifling (after reaming) and finish lap after rifling. All we do is cut rifling.

Later, Frank
Bartlein Barrels

It was obvious why the marks were on the lands, but how are they also in the grooves. I assumed that pulling a button through would displace and smooth out the marks in the grooves but, not so, thank you for your reply.

 

[Frank Green]

It was obvious why the marks were on the lands, but how are they also in the grooves. I assumed that pulling a button through would displace and smooth out the marks in the grooves but, not so, thank you for your reply.

That is one of the biggest misconceptions that the button rifling will displace and totally get rid of the tooling marks left over from the reamer.

One phrase that is used is that button rifling "will iron out the marks" It might to some extent but not always.

It goes back to.... Paying attention to the finish your getting out of the bore reamer. It's a big deal. At least to us it is. The nicer the finish the bore reamer leaves the less work you have to do to prelap the bore prior to rifling.

Here are a couple more pic's. The right pic shows the bore finish prior to a button being pulled thru. That finish isn't the greatest if that got bore reamed. Look close at that pic and you can see the bore reamer marks on the top of the lands.

Also you can see how the steel gets displaced and the stress it causes from the button going into the blank on the face of the barrel blank. Now try and imagine the stress induced into the blank. A good button maker will restress relieve the material after button rifling...and yes they are places that don't do it at all. Again residual stress in the blank no barrel maker can measure for.

For a rough number....a 30cal barrel that is suppose to have a .308" groove size...they might have to pull something like a .3115" button thru the blank. They get a different heat lot and that same button might not work and they might have to go to a .3120" diameter button. Also if they grab a different diameter blank that will play hell with the bore sizes. Going lets say from a 1.280" diameter blank to a 1.4" diameter blank the heavier wall thickness will make the bore/grooves tighten up and the opposite will happen if you go to a smaller diameter blank...the bore will get bigger.

 

[Tokay444]

Each impact of the hammers moves the steel along the mandrel incrementally.
The pattern is in the lands and in the grooves.
If the bore is not lapped afterwards, the pattern remains.

Button or cut rifling leaves a linear pattern.

That visible a pattern indicates a problem with the process.
Wasn't caught during final inspection or was ignored.
Hard to find good help, eh?


Note: I was just informed that too fast a speed in cutting the rifling can cause chatter marks also.

I have a button rifled Rock Creek barrel that has the exact same patter as well.