Indicating Barrels to chamber

[338 Mollett]

If the lands and the groves all look the same ,I'm satisfied with my work.

 

[tobnpr]

^^^
Yes- with CNC. Haven't seen anyone use it on a manual- perhaps someone has. I see no reason it would make a difference, other than larger CNC's would typically have more mass/rigidity than most of the manual machines we use.
My "problem" is that the top of my cross-slide is a removable cover to allow access to the screw/taper attachment. I'd need to machine a block with "legs" on either side to mount directly to the saddle; that would probably be an advantage in that there would be no need to confirm x-axis alignment with the DRO. It would need to be extremely rigid and repeatable when taken on/off for chambering. Fairly simple in concept, execution maybe not so much.

 

[Clark]

I'd put very little faith in this report. Current testing does not agree.

Can you show any test data to support your assertion?

 

[Alex Wheeler]

Can you show any test data to support your assertion?

What I can tell you is that in a match chamber. You only have a couple tenths around the bullet. Thats as far off center it can be from the bore (assuming the chamber is aligned with the bore). Myself and others I trust have tested our straightest ammo vs most crooked many times over the years. Usually thats something like less than .001" runout vs .005"-.006" runout or so. Still have never been able to shoot the difference. Its actually something I want to matter because we can improve it. We are using far more accurate rifles and ammunition tuned for the barrel. That article is talking about a relatively inaccurate rifle, with factory ammunition. Theres just too many variables. Its an interesting article, and someone took the time to put it the work. It could very well apply to a loose chamber and factory ammo, I don't know. I try to keep an open mind because enough people do seem concerned about runout. Maybe if the freebore diameter is really big like some chamberings it can allow the runout to show up more on target. But I still find it very hard to accept that the difference between .001" and .002" of bullet runout is worth .25 moa of accuracy like the chart shows in any rifle.

 

[Clark]

My father was chief engineer on the designs M55, M107, and M110 mobile artillery.
They put a strain gauge on the barrel to measure the stress of the bullet in chamber. If the bullet fell back [then showing less strain] and got an eccentric start when fired, terrible accuracy resulted.

He used a copy of Elements of Ordnance 1938

Elements of Ordnance: Textbook for the Use of the Cadets of the United States Military Academy.: Hayes, Maj. Gen. Thomas.: Amazon.com: Books

Elements of Ordnance: Textbook for the Use of the Cadets of the United States Military Academy. [Hayes, Maj. Gen. Thomas.] on Amazon.com. *FREE* shipping on qualifying offers. Elements of Ordnance: Textbook for the Use of the Cadets of the United States Military Academy.

www.amazon.com

I can only understand half of that book. It is not easy, unlike the NRA publication math.

 

[HillbillyLongRifle]

It took me awhile to put it all together but with the help of folks on here i can chamber barrels with nice and concentric throats and no measurable runout from breech to past the throat. I indicate off the bore and drill and bore before i use finish reamer pushed by dead center to establish the chamber. Hawkeye borescope tells the tale on the throat! I want a straight chamber and concentric throat the rest i have no control over inside that barrel. Ive chambered barrels different ways over the years but i have settled on my method now. The results speak for themselves

 

[Lucky Shooter]

Per Mr. Wheeler----"You have to establish a hole in the barrel thats concentric to the bore before you finish ream. Theres multiple ways to do that."

I've had good results by drilling a little short of the shoulder and a little under shoulder diameter,
followed by taper reaming------with compound set to track the reamer body slope.

This has worked well because, IMO. as the taper boring advances, the reamer can be placed into the hole far enough for the pilot to engage the targeted throat. At this point the reamer is held concentric at both ends. With a little more reamer pushing, some like to finish without the pilot, some like a smaller pilot and some like to keep it as is.

I'd like to get away from the taper boring and go to "straight in". Can anyone here describe
how this is done------with good results ?

This has been a good thread.

A. Weldy

 

[DaveTooley]

Per Mr. Wheeler----"You have to establish a hole in the barrel thats concentric to the bore before you finish ream. Theres multiple ways to do that."

I've had good results by drilling a little short of the shoulder and a little under shoulder diameter,
followed by taper reaming------with compound set to track the reamer body slope.

This has worked well because, IMO. as the taper boring advances, the reamer can be placed into the hole far enough for the pilot to engage the targeted throat. At this point the reamer is held concentric at both ends. With a little more reamer pushing, some like to finish without the pilot, some like a smaller pilot and some like to keep it as is.

I'd like to get away from the taper boring and go to "straight in". Can anyone here describe
how this is done------with good results ?

This has been a good thread.

A. Weldy

There two approaches to this. They depend of the taper in the body. On the occasion I have to use a drill bit instead of a caliber specific core drill I'll bore to different diameters. A case with plenty of taper I'll bore a short section to or just over shoulder diameter. In the case of a straighter case like a Creedmoor I bore to just under shoulder diameter for a some distance then a second shorter section to start the reamer at shoulder diameter. The reamer will go to the center of the trued hole unless forced off center.

 

[urbanrifleman]

There two approaches to this. They depend of the taper in the body. On the occasion I have to use a drill bit instead of a caliber specific core drill I'll bore to different diameters. A case with plenty of taper I'll bore a short section to or just over shoulder diameter. In the case of a straighter case like a Creedmoor I bore to just under shoulder diameter for a some distance then a second shorter section to start the reamer at shoulder diameter. The reamer will go to the center of the trued hole unless forced off center.

So, the key to make sure you get your chamber reamer to start beyond the part of the chamber that will be the throat?

 

[Dusty Stevens]

So, the key to make sure you get your chamber reamer to start beyond the part of the chamber that will be the throat?

Best thing you can do just starting out is ream it 100% and dont worry about drilling and boring at first

 

[urbanrifleman]

Best thing you can do just starting out is ream it 100% and dont worry about drilling and boring at first

There is that

 

[DaveTooley]

Best thing you can do just starting out is ream it 100% and dont worry about drilling and boring at first

Tough on the most important cutting part of the reamer. But yes that's an option.

 

[urbanrifleman]

Tough on the most important cutting part of the reamer. But yes that's an option.

I would not think pre drilling would be a big deal. The drill wants to follow the hole.

 

[Dusty Stevens]

Tough on the most important cutting part of the reamer. But yes that's an option.

It is tough but starting out hes not going to do many and tooling is just part of the tuition the way i see it.

 

[Alex Wheeler]

Tough on the most important cutting part of the reamer. But yes that's an option.

Its an option but if the back end of the barrel is running out, which it will be a little with most setups, the reamers will start out with a little bit of runout. A rigid setup would likely clean that up by the end, but I wouldnt count on a floating setup to every time. Just my opinion.

 

[urbanrifleman]

Its an option but if the back end of the barrel is running out, which it will be a little with most setups, the reamers will start out with a little bit of runout. A rigid setup would likely clean that up by the end, but I wouldnt count on a floating setup to every time. Just my opinion.

By back end you mean several inches inside the bore, or the other end of the barrel?

 

[butchlambert]

Backend would be toward the butt wouldn't it? I think he is saying with the back of the bore running out the back of the reamer would cut the chamber with a larger diameter.

 

[tobnpr]

I still have a "hangup" with using drill bits to pre-bore- which is the fact that when you bore the pre-drilled hole, you can't clean up the tapered cut at the end of the bit.
So you have a concentric bored hole, running right into the end of the hole cut by the drill bit, which isn't concentric and is still following the original bore. Apparently it makes no difference because seems everyone but me does it that way- but it still bugs me.

I use a teeny tiny Micro 100 boring bar that fits right into the bore, I clean up the rifling and then some for about 3/8" of an inch to guide the reamer. With the flush system, I'm not overly concerned about reamer wear. Like barrels, like tires on a car...I don't chamber dozens of barrels a month so it's not a consideration for me.

YMMV.

 

[Alex Wheeler]

Lets say you dial the throat and muzzle, the breach end will have a little runout. Maybe only .001" but it will have some. Same if you dial the throat and out in front of the throat. The straighter the bore the less it will have. You now start your reamer and pilot into bore that has runout. So the initial chamber will be running out to the the center of the spindle and the dialed sections of the bore. If the setup is rigid enough, if may over come that by the time the chamber is finished. If its a floating setup its unlikely. Just think about what is happening and what your trying to achieve. Dont listen to what I say, try to learn the whys of machining practices and everything will become very simple.

 

[urbanrifleman]

Lets say you dial the throat and muzzle, the breach end will have a little runout. Maybe only .001" but it will have some. Same if you dial the throat and out in front of the throat. The straighter the bore the less it will have. You now start your reamer and pilot into bore that has runout. So the initial chamber will be running out the the center of the spindle and the dialed sections of the bore. If the setup is rigid enough, if may over come that by the time the chamber is finished. If its a floating setup its a coin toss.

Don't you dial the breech (say an inch in) and a point beyond the throat (or as far as you can reach with the indicator)?

I never understood dialing the muzzle to zero on the other end of the barrel... the barrel is crooked to some extent, that is a given, the only thing of interest would be the part where the chamber sits, right?

Forgive me. I am just trying to ask good questions... maybe I am failing. I admit some of the things I have heard about dialing in barrels makes exactly zero sense to me.