more debate on chamber reaming

I did regrinding on precision spindle tapers for machine tools (mostly cat 40's and 50's) and taper pins (#4's - #10) to locate parts on the machine tools as well. I have never chambered a gun in my life! O.k. that being said I'm trying to apply my 30yr of industrial experience to lead toward chambering my first benchrest rifle attempt. First off I'd like to comment on the pilot on a chamber reamer. If it is loose fitting enough (sloppy) to spin freely in a rifle bore then I.M.H.O. it can and will lead to angular misalignment of the finished chamber. Now couple the other end with a floating reamer holder and i think this is a lowest cost, most easily done chamber for the home machinist. maybe not what I want to do to my high cost, hand lapped rifle barrel that's supposed to shoot 1/4 MOA. Other people on this board have had some really good ideas/tricks, as well. I would welcome any/all comments on this subject.

i am getting close to chambering my first barrel and am reading as much as i can on the subject. i purchased a ptg reamer and a pilot bushing kit. the bushings are in .0002" increments. it looks to me like the bushing rides on the rifling and spins on a shank on the reamer. with a bushing sized exactly to the bore, i don't see there being much misalignment. i do think that using a center in the tailstock to push the reamer would be the best method IF the tailstock height were perfect. i know on my chinese lathe the tailstock height can change a few tenths from morning to the heat of the day. i am going to use a "bald eagle" floating reamer holder to do mine. i can't justify a high dollar holder for a single rifle build for myself. i definatly can't afford a high quality lathe and climate controlled shop.

there were a few people on the other thread that set their barrel up on the lathe like i am planning on. i like the idea of using a four jaw chuck and a spider/cathead at the back of the spindle. from what i have heard many people say, the bore is almost never perfectly straight through the barrel. having the barrel through the spindle and using a properly fitted range rod with two indicators at the chamber end to dial it to less than .0002" sounds like the best way to set up the barrel. with this method there is no need to indicate the muzzle end. in this setup the shank and threads can be turned and the chamber cut. this will ensure the shank and chamber are aligned with the bore at that point which sounds most critical to me. using the same method for the crown sounds like the best method to me also.

again, i have not even chambered my first barrel yet. this is just the information that i have picked to be the best after reading everything i could find on the subject. if someone has a better, more accurate way to do this, i'd love to hear it.

300 sniper

I would suggest cutting 1 inch of both chamber/muzzle ends before dialing to .0001 or less because of lapping tolerances. Why have a cat head at the back if not dialed your only achieving a barrel with greater angular detection with no movement and less chances of yawning. I would dial both ends for chambering and crowning to insure chamber and crown are both perpendicular and parallel to the bore. (unfortunately we have no control over bores that are not straight)

wal

To dial in the muzzle end is one thing, cause you don't want the muzzle to be in the wrong direction.
But to actually move the muzzle with the muzzle spider when the shank is chucket so the dial looks right is wrong.
That is only archiving a temporary bent barrel and is adding nothing good to the rebarrelwork.

Technika

Technika

Tell me how would chambering a barrel that is .0001 TIR at the muzzle and chamber, and cant yaw at either end "add nothing good to a chamber job"?

wal

www.technika.nu said:

To dial in the muzzle end is one thing, cause you don't want the muzzle to be in the wrong direction.
But to actually move the muzzle with the muzzle spider when the shank is chucket so the dial looks right is wrong.
That is only archiving a temporary bent barrel and is adding nothing good to the rebarrelwork.

Technika

Click to expand...

The barrel is chucked on pieces on pieces of copper wire in the grooves of the jaws so it is allowed to move left,right ,up and down when the other end is dialed in.I do the same thing when using a steady rest to do a chamber.

I like your chucking idea that allows angular displacement of the chamber end. After all, the entire centering process involves an averaging of mis-tolerances. The chamber end takes precedence, though, IMHO.
F

Gentle, since you are the grinding guru, dial in the bore and grind the chamber, then let us all know how well it shoots!

I don't pop into the gunsmith forum often, and I know nothing about this, but really, has anyone ever done this? If you are going for sub micron tolerances, grinding is the only way to go. I know our Hardinge Conquest SP held 8 millionths when new (at least the 3 brass test bars were...that's just ), but if I were to try to hold something to super tight tolerances, I'd be looking at a new methodology...gun drill, rifle, rough bore the chamber, grind the chamber, turn the OD and grind the threads and shoulder in one set up. The OD profiling and muzzle end would be the only secondary ops.

Steve

Maybe hi-jacking a little but as not being a pro gunsmith or even ever chambered a barrel but just being an novice, I sometimes feel in these discusions that Method becomes more important than the Objective. Not that it is not of interest. I think most of us here are just as interested in the How´s and With What as what were are actually producing?

Just let me ask you two questions to see if I have understood anything at all....

1´st
The bullet shall be concentric with the centerline of the bore upon impact with the lands. The centerline of the face of the lands is also to be concentric to the bore.

2´nd
The case head shall impact the breech perpendicularly for suitable stress distribution in the action.

Am I totally off here or missing something obvius out?

Have a nice evening!

wal said:

300 sniper

I would suggest cutting 1 inch of both chamber/muzzle ends before dialing to .0001 or less because of lapping tolerances. Why have a cat head at the back if not dialed your only achieving a barrel with greater angular detection with no movement and less chances of yawning. I would dial both ends for chambering and crowning to insure chamber and crown are both perpendicular and parallel to the bore. (unfortunately we have no control over bores that are not straight)

wal

Click to expand...

if you are using two indicators at the chamber end on a range rod and a spider on the muzzle end, the reamer should be entering the bore at that point as straight as possible. sure the bore may be curved but i would think reaming concentric to the bore at that end of the barrel is more critical than along an imaginary line through the ends of the bore. this also allows the threads to be turned perfectly concentric to the bore at that point.

with your method, if you dial the barrel in to .0001" using a single indicator on each end, how much runout will you have if you move the indicator 3" further out on the range rod? i hope i don't sound argumentative, i am trying to figure out the best method for this before i start cutting on an expensive barrel. your method seems to me like it would have more error unless the bore was absolutely straight from breach to muzzle. i could be wrong, it has happened before.

deltaenterprizes said:

The barrel is chucked on pieces on pieces of copper wire in the grooves of the jaws so it is allowed to move left,right ,up and down when the other end is dialed in.I do the same thing when using a steady rest to do a chamber.

Click to expand...

i had not even thought about the spider bending the barrel because the length of the flat gripping surface of a 4 jaw chuck. the wire idea is great and i am glad you mentioned it.

thanks.

300sniper

I think you mis understood i wasnt suggesting reaming to an imaginary line of the bore. I was suggesting to hold and dial the barrel as true as possible to reduce angular detection and barrel yaw. Think about what happens when you bore your barrel, your only boring to your point of indication where your pilot and reamer are going to follow!! Hopefully i dont have to elborate anymore.

wal

wal said:

300sniper

I think you mis understood i wasnt suggesting reaming to an imaginary line of the bore. I was suggesting to hold and dial the barrel as true as possible to reduce angular detection and barrel yaw. Think about what happens when you bore your barrel, your only boring to your point of indication where your pilot and reamer are going to follow!! Hopefully i dont have to elborate anymore.

wal

Click to expand...

maybe i am misunderstanding you. are you using a single indicator on a range rod at the chamber end or two?

300sniper

single indicator

wal

300sniper'
I indicate on the grooves in the throat. I drill and taper bore to that point. If you would have read my previous chambering post it is explained for you. I hate to have to go over it again. The thing that is important is for the bullet to see a bore that is concentric to the axis of the bearings of the headstock. A range rod has a floating bushing on the end and the rod is tapered. Your bushings are ground with a .0002 clearance to the reamer. A bushing has at least .0002 clearance to the bore to enable you to push it into the bore. You cannot put a .237 bushing for example into a .237 hole unless it is forced. If you haven't worked in a machine shop then some of this is strange to you. Also some of the machineshop guys that haven't chambered a barrel are not aware of some of the things we have to deal with.
On grinding a chamber, First it is cost prohibitive. Second it has the same problems that you would run into with a CNC lathe. On a short cartridge like a 6ppc you would have to have a tool that will reach about 1.560 and the final cut would be .237id at the bore. Most necks are .262 or so in diameter and that starts at about 1.180" into the hole and will need to reach in and grind a straight from there to 1.500 at a diameter of .262 and then a 1.5degree leed angle to 1.560 holding .0001.
Butch

i don't see how a barrel could be set up better than one dialed in with a range rod with a properly fitted bushing inserted about 2.5"-3" into the bore and an indicator just outside the bore and one about 3" outside. i am failing to see how that is not the most accurate way. i don't see how indicating the muzzle end will help when you are chambering 28" away. if the bore is less than straight, moving the indicator along the range rod would give different readings, correct? if so this would mean that your shank/threads will not be concentric with the bore at that point, only at the point you originally had your indicator.


again, maybe i am misunderstanding something which is very possible since i am new to this all.

edit: butch's post came in while i was writing mine. mine was in response to wal's post above. now i am off to re-read butch's previous chambering post.

floating reamer holder

Everyone talks about buying a high priced reamer holder, I buy mine at Lowes but they call them ball bearings. Jerrel

Butch Lambert said:

300sniper'
I indicate on the grooves in the throat. I drill and taper bore to that point. If you would have read my previous chambering post it is explained for you. I hate to have to go over it again. *snip*

Click to expand...

i won't make you go over it again. i just went back and read your post in the other thread. now that sounds like an accurate set up. out of curiosity, how much run out do you usually find in the grooves after your initial set up?

300sniper

Having to elaborate, when dialing the bore i dial it in the throat of the chamber then drill/bore to that TIR.(.0001 or less)
Having both ends dialed reduces angular detection of the bore. The reason i suggested cutting both ends of the barrel was because most gunsmiths only indicate the start of the chamber, usually due to lack of measuring equipment. I appoligise for not being thorough in my previous threads.

wal

Ive had an idea! which could be dangerous, and I wonder what you guys may think? as it could relate to chambering. Ive heard it said (which maynot be true) that to drill and ream a hole as true as possible its better to have both the material and the tool live, I wonder if that could work in chambering and would you realy gain anything over conventional methods? that would mean that the barrel turns as normal, but the reamer is also turning (driven). Another reason why I ask is because I have a spare variable bridgport type milling head and was thinking of adapting it to fit my lathe ways at 90 degrees and using it instead of a tailstock , that way I could use the quills power drive at its slowest feed to run in the reamer at a set depth, which would spring out when reached for me to clear the chips and repeat until desired. Initially I imagine this type of setup would chatter? who knows, perhaps someone has already tried it?

KB

wal said:

300sniper

Having to elaborate, when dialing the bore i dial it in the throat of the chamber then drill/bore to that TIR.(.0001 or less)
Having both ends dialed reduces angular detection of the bore. The reason i suggested cutting both ends of the barrel was because most gunsmiths only indicate the start of the chamber, usually due to lack of measuring equipment. I appoligise for not being thorough in my previous threads.

wal

Click to expand...

i see. that makes more sense to me. i had no idea that people were going as far as dialing in the throat. i figured that the range rod fit to the lands was as good as it could get but like butch mentioned, there are a few small clearances that will compound.

cutting the ends of the barrel off makes sense to me. i was planning on cutting 1.25+ off of the muzzle end because of the lapping but had not considered cutting the chamber end since the reamer would be removing that. it makes sense to cut the chamber end also for indicating the true bore.

now i have more money to spend on the indicator butch mentioned. i know my .0001" indicators won't reach the throat.