Excessive Runout on New Barrel When Chambering

[Alex Wheeler]

Here's what I see often. This not the worst example I've had but this is what I found on my hard drive on short notice. How should this be interpreted? Same barrel, images about 180 degrees apart.

I don't want to derail this thread so I'll bow out here. When I first replied I actually thought I was in a different thread. Sorry.

Chamber not concentric to the throat. Rifling back to the neck on one side and freebore on the other. Barrel not dialed in properly, a pilot cant fix that. Even if you dial the throat perfect but the bore in front of it (where the pilot is) is running out you will end up with this if you use a tight fitting pilot. Setup is critical and takes time. For there to be any profit in inexpensive prefits, corners have to be cut.

 

[butchlambert]

It’s extremely easy to flex a barrel into submission leading to exaggerated muzzle runout during chambering. It’s also possible to have the angle of the bore (during crowning) cancel out any expected runout that was experienced during chambering.

You can flex it if using chuck jaws only on 1 end. I have catheads on each end with copper tips on the screws.

 

[JPB3]

Over the years I'm sure individual chambering methods evolve as smiths find what works for them and their equipment.. I've tried a few different methods and like Dave T. I indicate the bore and the muzzle as close as I can get it.. Thread and chamber. Started this in 1992, I think. It's very unusual to have a finished chamber exhibit over .0003-.0004 runout. Most are much better. I've chambered a lot of very accurate barrels and still have most of my hair! I have known some excellent shooters who indicate two spots in the chamber end and muzzle runout be damned.. I didn't see any difference on the target between the two methods and found indicating the muzzle end and the chamber end more to my liking. Good luck with your barrel.

 

[butchlambert]

Over the years I'm sure individual chambering methods evolve as smiths find what works for them and their equipment.. I've tried a few different methods and like Dave T. I indicate the bore and the muzzle as close as I can get it.. Thread and chamber. Started this in 1992, I think. It's very unusual to have a finished chamber exhibit over .0003-.0004 runout. Most are much better. I've chambered a lot of very accurate barrels and still have most of my hair! I have known some excellent shooters who indicate two spots in the chamber end and muzzle runout be damned.. I didn't see any difference on the target between the two methods and found indicating the muzzle end and the chamber end more to my liking. Good luck with your barrel.

Runout? Are you speaking of an egg shaped chamber or?

 

[JPB3]

Beats the hell out of me Butch, stick an indicator in a finished chamber and see what it does..
In my lathe most chambers will have .0002'' or less of indicator movement after I finish reaming.. Hell, could be in the bearings..
Pat

 

[Bob3700]

If the chamber is indicated to .0002” runout and the muzzle end then shows .030” runout, would that not show the bore/ bbl. is curved/ bent?
Many a thread have argued that bent bbls. No longer exist.
Maybe it is just terms/nomenclature That are confusing me.

 

[Tokay444]

If the chamber is indicated to .0002” runout and the muzzle end then shows .030” runout, would that not show the bore/ bbl. is curved/ bent?
Many a thread have argued that bent bbls. No longer exist.
Maybe it is just terms/nomenclature That are confusing me.

There’s no such thing as a straight hole. Some are just straighter than others. Go to enough decimal places, and they’re all curved.

 

[DaveTooley]

I can't speak for all barrel makers but I do know Bartlein's cutter boxes are .0004" under the bore diameter. Considering their length if there was much curvature they would have an interference fit. They also hone each bore to size which makes them round and straightens them out. If my memory is correct the stones are about 2" long.

 

[tobnpr]

A properly setup barrel, a properly roughed in chamber doesn't require a bushing on the reamer.

OK...
Clarify?
Your Haas setup is rigid, or floating holder?
Speeds, feeds, peck depth?

Bucking the common "wisdom", I've gotten better results not pre-boring. Snug fitting pilot ( my experience has been a chatter nightmare otherwise), turn on the oil flush and drive the reamer with a floating holder.

I've pre-bored a couple of times with mixed results. Once I'm pretty sure I failed to clean up the drilled hole completely which was the cause of the runout, and the other time I think the setup moved. Neither was a failure- but I'm just not sold on the "gotta pre-bore" mantra. If I didn't use a flush system it would be a huge advantage/time saver. I get the results I want without doing it, and have no incentive to reduce chambering time further.

 

[butchlambert]

OK...
Clarify?
Your Haas setup is rigid, or floating holder?
Speeds, feeds, peck depth?

Bucking the common "wisdom", I've gotten better results not pre-boring. Snug fitting pilot ( my experience has been a chatter nightmare otherwise), turn on the oil flush and drive the reamer with a floating holder.

I've pre-bored a couple of times with mixed results. Once I'm pretty sure I failed to clean up the drilled hole completely which was the cause of the runout, and the other time I think the setup moved. Neither was a failure- but I'm just not sold on the "gotta pre-bore" mantra. If I didn't use a flush system it would be a huge advantage/time saver. I get the results I want without doing it, and have no incentive to reduce chambering time further.

What Dave is saying, he can correct me if I misunderstood, If you indicate the throat and muzzle, the reamer will follow the prebored hole and not a tight bushing that is guiding the reamer that is sticking out 3/4" beyond the throat.
I don't think you can purposely drill a barrel and ream it in a flat curve. They may follow a helix, but not a constant helix either. It may take off in one direction and then settle down or get worse. This is probably talked about too much. Just get your barrel properly set up and all will be good.

 

[DaveTooley]

OK...
Clarify?
Your Haas setup is rigid, or floating holder?
Speeds, feeds, peck depth?

Bucking the common "wisdom", I've gotten better results not pre-boring. Snug fitting pilot ( my experience has been a chatter nightmare otherwise), turn on the oil flush and drive the reamer with a floating holder.

I've pre-bored a couple of times with mixed results. Once I'm pretty sure I failed to clean up the drilled hole completely which was the cause of the runout, and the other time I think the setup moved. Neither was a failure- but I'm just not sold on the "gotta pre-bore" mantra. If I didn't use a flush system it would be a huge advantage/time saver. I get the results I want without doing it, and have no incentive to reduce chambering time further.

As I said I set the barrel up the same as a manual machine and finish ream the same way. With a pusher. I get no wobble in the reamer handle. I don't use that cutting fluid any longer. Wasn't good for my health.

 

[Alex Wheeler]

If the throat is truly dialed in, and chamber drilled and prebored, you would have to try really harm to mess that up. I really think most guys problem is they are not dialed in as well as they think.

 

[Tokay444]

Generally, a high-speed steel reamer is just going to follow the hole it’s reaming.